298604 : Split the p2QL into one core simple Expression part and one Query part

74 files changed, 1205 insertions, 3673 deletions

diff --git a/bundles/org.eclipse.equinox.p2.ql/.settings/.api_filters b/bundles/org.eclipse.equinox.p2.ql/.settings/.api_filters
new file mode 100644
index 000000000..dfbf53e91
--- /dev/null
+++ b/bundles/org.eclipse.equinox.p2.ql/.settings/.api_filters
@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<component id="org.eclipse.equinox.p2.ql" version="2">
+    <resource path="src/org/eclipse/equinox/internal/p2/ql/expression/WrappedIQuery.java" type="org.eclipse.equinox.internal.p2.ql.expression.WrappedIQuery">
+        <filter id="640712815">
+            <message_arguments>
+                <message_argument value="IMatchQuery&lt;T&gt;"/>
+                <message_argument value="WrappedIQuery"/>
+                <message_argument value="isMatch(T)"/>
+            </message_arguments>
+        </filter>
+    </resource>
+    <resource path="src/org/eclipse/equinox/p2/ql/QLMatchQuery.java" type="org.eclipse.equinox.p2.ql.QLMatchQuery">
+        <filter id="574619656">
+            <message_arguments>
+                <message_argument value="IMatchQuery&lt;T&gt;"/>
+                <message_argument value="QLMatchQuery&lt;T&gt;"/>
+            </message_arguments>
+        </filter>
+    </resource>
+    <resource path="src/org/eclipse/equinox/p2/ql/QLQuery.java" type="org.eclipse.equinox.p2.ql.QLQuery">
+        <filter id="574619656">
+            <message_arguments>
+                <message_argument value="IQuery&lt;T&gt;"/>
+                <message_argument value="QLQuery&lt;T&gt;"/>
+            </message_arguments>
+        </filter>
+    </resource>
+</component>
diff --git a/bundles/org.eclipse.equinox.p2.ql/META-INF/MANIFEST.MF b/bundles/org.eclipse.equinox.p2.ql/META-INF/MANIFEST.MF
index da22b4c74..8eb989b7d 100644
--- a/bundles/org.eclipse.equinox.p2.ql/META-INF/MANIFEST.MF
+++ b/bundles/org.eclipse.equinox.p2.ql/META-INF/MANIFEST.MF
@@ -12,9 +12,12 @@ Bundle-RequiredExecutionEnvironment: J2SE-1.5,
 Bundle-ActivationPolicy: lazy
 Import-Package: org.eclipse.equinox.internal.p2.core.helpers,
  org.eclipse.equinox.internal.p2.metadata,
+ org.eclipse.equinox.internal.p2.metadata.expression,
+ org.eclipse.equinox.internal.p2.metadata.expression.parser,
  org.eclipse.equinox.internal.p2.query,
  org.eclipse.equinox.internal.provisional.p2.metadata,
  org.eclipse.equinox.p2.metadata,
+ org.eclipse.equinox.p2.metadata.expression,
  org.eclipse.equinox.p2.metadata.query,
  org.eclipse.equinox.p2.query,
  org.eclipse.equinox.p2.repository.artifact,
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/CapabilityIndex.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/CapabilityIndex.java
index e6b3f74bf..ccb132be1 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/CapabilityIndex.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/CapabilityIndex.java
@@ -23,34 +23,24 @@ public class CapabilityIndex implements ICapabilityIndex {
 
 	private final Map<String, Object> capabilityMap;
 
-	private static class IUCapability {
-		final IInstallableUnit iu;
-		final IProvidedCapability capability;
-
-		IUCapability(IInstallableUnit iu, IProvidedCapability capability) {
-			this.iu = iu;
-			this.capability = capability;
-		}
-	}
-
+	@SuppressWarnings("unchecked")
 	public CapabilityIndex(Iterator<IInstallableUnit> itor) {
 		HashMap<String, Object> index = new HashMap<String, Object>();
 		while (itor.hasNext()) {
 			IInstallableUnit iu = itor.next();
 			Collection<IProvidedCapability> pcs = iu.getProvidedCapabilities();
 			for (IProvidedCapability pc : pcs) {
-				IUCapability iuCap = new IUCapability(iu, pc);
 				String name = pc.getName();
-				Object prev = index.put(name, iuCap);
+				Object prev = index.put(name, iu);
 				if (prev != null) {
-					ArrayList<IUCapability> lst;
+					ArrayList<IInstallableUnit> lst;
 					if (prev instanceof ArrayList<?>)
-						lst = (ArrayList<IUCapability>) prev;
+						lst = (ArrayList<IInstallableUnit>) prev;
 					else {
-						lst = new ArrayList<IUCapability>(4);
-						lst.add((IUCapability) prev);
+						lst = new ArrayList<IInstallableUnit>(4);
+						lst.add((IInstallableUnit) prev);
 					}
-					lst.add(iuCap);
+					lst.add(iu);
 					index.put(name, lst);
 				}
 			}
@@ -65,7 +55,7 @@ public class CapabilityIndex implements ICapabilityIndex {
 		List<IInstallableUnit> collector = new ArrayList<IInstallableUnit>();
 		do {
 			IRequirement nxt = requirements.next();
-			collectMatchingIUs((IRequiredCapability) nxt, collector);
+			collectMatchingIUs(nxt, collector);
 		} while (requirements.hasNext());
 		return collector.iterator();
 	}
@@ -85,22 +75,22 @@ public class CapabilityIndex implements ICapabilityIndex {
 	private void collectMatchingIUs(IRequirement requirement, Collection<IInstallableUnit> collector) {
 		if (!(requirement instanceof IRequiredCapability))
 			return;
-		IRequiredCapability rc = (IRequiredCapability) requirement;
-		Object v = capabilityMap.get(rc.getName());
+		Object v = capabilityMap.get(((IRequiredCapability) requirement).getName());
 		if (v == null)
 			return;
 
-		if (v instanceof IUCapability) {
-			IUCapability iuc = (IUCapability) v;
-			if (iuc.capability.satisfies(requirement))
-				collector.add(iuc.iu);
+		if (v instanceof IInstallableUnit) {
+			IInstallableUnit iu = (IInstallableUnit) v;
+			if (iu.satisfies(requirement))
+				collector.add(iu);
 		} else {
-			List<IUCapability> iucs = (List<IUCapability>) v;
-			int idx = iucs.size();
+			@SuppressWarnings("unchecked")
+			List<IInstallableUnit> ius = (List<IInstallableUnit>) v;
+			int idx = ius.size();
 			while (--idx >= 0) {
-				IUCapability iuc = iucs.get(idx);
-				if (iuc.capability.satisfies(requirement))
-					collector.add(iuc.iu);
+				IInstallableUnit iu = ius.get(idx);
+				if (iu.satisfies(requirement))
+					collector.add(iu);
 			}
 		}
 	}
@@ -109,28 +99,28 @@ public class CapabilityIndex implements ICapabilityIndex {
 		if (!(requirement instanceof IRequiredCapability))
 			return CollectionUtils.emptySet();
 
-		IRequiredCapability rc = (IRequiredCapability) requirement;
-		Object v = capabilityMap.get(rc.getName());
+		Object v = capabilityMap.get(((IRequiredCapability) requirement).getName());
 		if (v == null)
 			return CollectionUtils.emptySet();
 
 		Set<IInstallableUnit> retained = null;
-		if (v instanceof IUCapability) {
-			IUCapability iuc = (IUCapability) v;
-			if (iuc.capability.satisfies(requirement) && collector.contains(iuc.iu)) {
+		if (v instanceof IInstallableUnit) {
+			IInstallableUnit iu = (IInstallableUnit) v;
+			if (iu.satisfies(requirement) && collector.contains(iu)) {
 				if (retained == null)
 					retained = new HashSet<IInstallableUnit>();
-				retained.add(iuc.iu);
+				retained.add(iu);
 			}
 		} else {
-			List<IUCapability> iucs = (List<IUCapability>) v;
-			int idx = iucs.size();
+			@SuppressWarnings("unchecked")
+			List<IInstallableUnit> ius = (List<IInstallableUnit>) v;
+			int idx = ius.size();
 			while (--idx >= 0) {
-				IUCapability iuc = iucs.get(idx);
-				if (iuc.capability.satisfies(requirement) && collector.contains(iuc.iu)) {
+				IInstallableUnit iu = ius.get(idx);
+				if (iu.satisfies(requirement) && collector.contains(iu)) {
 					if (retained == null)
 						retained = new HashSet<IInstallableUnit>();
-					retained.add(iuc.iu);
+					retained.add(iu);
 				}
 			}
 		}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/Everything.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/Everything.java
index 4f3fc819b..d127bf72a 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/Everything.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/Everything.java
@@ -10,6 +10,10 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql;
 
+import org.eclipse.equinox.internal.p2.metadata.expression.IRepeatableIterator;
+
+import org.eclipse.equinox.internal.p2.metadata.expression.RepeatableIterator;
+
 import java.util.Collection;
 import java.util.Iterator;
 import org.eclipse.equinox.internal.p2.core.helpers.CollectionUtils;
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/FlattenIterator.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/FlattenIterator.java
index f41e20c1b..179a36613 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/FlattenIterator.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/FlattenIterator.java
@@ -10,6 +10,8 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql;
 
+import org.eclipse.equinox.internal.p2.metadata.expression.RepeatableIterator;
+
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/IRepeatableIterator.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/IRepeatableIterator.java
deleted file mode 100644
index 1f8fa8655..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/IRepeatableIterator.java
+++ /dev/null
@@ -1,25 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql;
-
-import java.util.Iterator;
-
-public interface IRepeatableIterator<T> extends Iterator<T> {
-	/**
-	 * Returns a copy that will iterate over the same elements
-	 * as this iterator. The contents or position of this iterator
-	 * is left unchanged. 
-	 * @return A re-initialized copy of this iterator.
-	 */
-	IRepeatableIterator<T> getCopy();
-
-	Object getIteratorProvider();
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/MultiVariableContext.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/MultiVariableContext.java
deleted file mode 100644
index 8218e76d6..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/MultiVariableContext.java
+++ /dev/null
@@ -1,51 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql;
-
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-import org.eclipse.equinox.p2.ql.IExpression;
-
-public final class MultiVariableContext implements IEvaluationContext {
-	private final IEvaluationContext parentContext;
-
-	private final Object[] values;
-
-	public MultiVariableContext(IEvaluationContext parentContext, IExpression[] variables) {
-		this.parentContext = parentContext;
-		values = new Object[variables.length * 2];
-		for (int idx = 0, ndx = 0; ndx < variables.length; ++ndx, idx += 2)
-			values[idx] = variables[ndx];
-	}
-
-	public Object getParameter(int position) {
-		return parentContext.getParameter(position);
-	}
-
-	public Object getParameter(String key) {
-		return parentContext.getParameter(key);
-	}
-
-	public Object getValue(IExpression variable) {
-		for (int idx = 0; idx < values.length; ++idx)
-			if (values[idx++] == variable)
-				return values[idx];
-		return parentContext.getValue(variable);
-	}
-
-	public void setValue(IExpression variable, Object value) {
-		for (int idx = 0; idx < values.length; ++idx)
-			if (values[idx++] == variable) {
-				values[idx] = value;
-				return;
-			}
-		parentContext.setValue(variable, value);
-	}
-}
\ No newline at end of file
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/ParameterContext.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/ParameterContext.java
deleted file mode 100644
index 653c103ad..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/ParameterContext.java
+++ /dev/null
@@ -1,44 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql;
-
-import java.util.Map;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-import org.eclipse.equinox.p2.ql.IExpression;
-
-/**
- * The immutable top level context used when evaluating an expression.
- */
-public final class ParameterContext implements IEvaluationContext {
-	private static final Object[] noParameters = new Object[0];
-
-	private final Object[] parameters;
-
-	public ParameterContext(Object[] parameters) {
-		this.parameters = parameters == null ? noParameters : parameters;
-	}
-
-	public Object getParameter(int position) {
-		return parameters[position];
-	}
-
-	public Object getParameter(String key) {
-		return parameters.length == 1 && parameters[0] instanceof Map<?, ?> ? ((Map<?, ?>) parameters[0]).get(key) : null;
-	}
-
-	public Object getValue(IExpression variable) {
-		throw new IllegalArgumentException("No such variable: " + variable); //$NON-NLS-1$
-	}
-
-	public void setValue(IExpression variable, Object value) {
-		throw new IllegalArgumentException("No such variable: " + variable); //$NON-NLS-1$
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/QueryContext.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/QueryContext.java
index 2f82b3f25..0f8f63cf2 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/QueryContext.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/QueryContext.java
@@ -3,6 +3,8 @@ package org.eclipse.equinox.internal.p2.ql;
 import java.util.*;
 import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.NullProgressMonitor;
+import org.eclipse.equinox.internal.p2.metadata.expression.IRepeatableIterator;
+import org.eclipse.equinox.internal.p2.metadata.expression.RepeatableIterator;
 import org.eclipse.equinox.p2.metadata.IInstallableUnit;
 import org.eclipse.equinox.p2.ql.IQueryContext;
 import org.eclipse.equinox.p2.ql.ITranslationSupport;
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/RepeatableIterator.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/RepeatableIterator.java
deleted file mode 100644
index 7c1a83500..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/RepeatableIterator.java
+++ /dev/null
@@ -1,237 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql;
-
-import java.util.*;
-import org.eclipse.equinox.p2.query.IQueryResult;
-
-public class RepeatableIterator<T> implements IRepeatableIterator<T> {
-	private final List<T> values;
-	private int position = -1;
-
-	@SuppressWarnings("unchecked")
-	public static <T> IRepeatableIterator<T> create(Object unknown) {
-		if (unknown.getClass().isArray())
-			return create((T[]) unknown);
-		if (unknown instanceof Iterator<?>)
-			return create((Iterator<T>) unknown);
-		if (unknown instanceof List<?>)
-			return create((List<T>) unknown);
-		if (unknown instanceof Collection<?>)
-			return create((Collection<T>) unknown);
-		if (unknown instanceof Map<?, ?>)
-			return create((Set<T>) ((Map<?, ?>) unknown).entrySet());
-		if (unknown instanceof IQueryResult<?>)
-			return create((IQueryResult<T>) unknown);
-		throw new IllegalArgumentException("Cannot convert a " + unknown.getClass().getName() + " into an iterator"); //$NON-NLS-1$ //$NON-NLS-2$
-	}
-
-	public static <T> IRepeatableIterator<T> create(Iterator<T> iterator) {
-		return iterator instanceof IRepeatableIterator<?> ? ((IRepeatableIterator<T>) iterator).getCopy() : new ElementRetainingIterator<T>(iterator);
-	}
-
-	public static <T> IRepeatableIterator<T> create(List<T> values) {
-		return new RepeatableIterator<T>(values);
-	}
-
-	public static <T> IRepeatableIterator<T> create(Collection<T> values) {
-		return new CollectionIterator<T>(values);
-	}
-
-	public static <T> IRepeatableIterator<T> create(IQueryResult<T> values) {
-		return new QueryResultIterator<T>(values);
-	}
-
-	public static <T> IRepeatableIterator<T> create(T[] values) {
-		return new ArrayIterator<T>(values);
-	}
-
-	RepeatableIterator(List<T> values) {
-		this.values = values;
-	}
-
-	public IRepeatableIterator<T> getCopy() {
-		return new RepeatableIterator<T>(values);
-	}
-
-	public boolean hasNext() {
-		return position + 1 < values.size();
-	}
-
-	public T next() {
-		if (++position == values.size()) {
-			--position;
-			throw new NoSuchElementException();
-		}
-		return values.get(position);
-	}
-
-	public void remove() {
-		throw new UnsupportedOperationException();
-	}
-
-	public Object getIteratorProvider() {
-		return values;
-	}
-
-	void setPosition(int position) {
-		this.position = position;
-	}
-
-	List<T> getValues() {
-		return values;
-	}
-
-	static class ArrayIterator<T> implements IRepeatableIterator<T> {
-		private final T[] array;
-		private int position = -1;
-
-		public ArrayIterator(T[] array) {
-			this.array = array;
-		}
-
-		public Object getIteratorProvider() {
-			return array;
-		}
-
-		public boolean hasNext() {
-			return position + 1 < array.length;
-		}
-
-		public T next() {
-			if (++position >= array.length)
-				throw new NoSuchElementException();
-			return array[position];
-		}
-
-		public void remove() {
-			throw new UnsupportedOperationException();
-		}
-
-		public IRepeatableIterator<T> getCopy() {
-			return new ArrayIterator<T>(array);
-		}
-	}
-
-	static class CollectionIterator<T> implements IRepeatableIterator<T> {
-		private final Collection<T> collection;
-
-		private final Iterator<T> iterator;
-
-		CollectionIterator(Collection<T> collection) {
-			this.collection = collection;
-			this.iterator = collection.iterator();
-		}
-
-		public IRepeatableIterator<T> getCopy() {
-			return new CollectionIterator<T>(collection);
-		}
-
-		public Object getIteratorProvider() {
-			return collection;
-		}
-
-		public boolean hasNext() {
-			return iterator.hasNext();
-		}
-
-		public T next() {
-			return iterator.next();
-		}
-
-		public void remove() {
-			throw new UnsupportedOperationException();
-		}
-	}
-
-	static class QueryResultIterator<T> implements IRepeatableIterator<T> {
-		private final IQueryResult<T> queryResult;
-
-		private final Iterator<T> iterator;
-
-		QueryResultIterator(IQueryResult<T> queryResult) {
-			this.queryResult = queryResult;
-			this.iterator = queryResult.iterator();
-		}
-
-		public IRepeatableIterator<T> getCopy() {
-			return new QueryResultIterator<T>(queryResult);
-		}
-
-		public Object getIteratorProvider() {
-			return queryResult;
-		}
-
-		public boolean hasNext() {
-			return iterator.hasNext();
-		}
-
-		public T next() {
-			return iterator.next();
-		}
-
-		public void remove() {
-			throw new UnsupportedOperationException();
-		}
-	}
-
-	static class ElementRetainingIterator<T> extends RepeatableIterator<T> {
-
-		private Iterator<T> innerIterator;
-
-		ElementRetainingIterator(Iterator<T> iterator) {
-			super(new ArrayList<T>());
-			innerIterator = iterator;
-		}
-
-		public synchronized boolean hasNext() {
-			if (innerIterator != null) {
-				if (innerIterator.hasNext())
-					return true;
-				innerIterator = null;
-				setPosition(getValues().size());
-			}
-			return super.hasNext();
-		}
-
-		public synchronized T next() {
-			if (innerIterator != null) {
-				T val = innerIterator.next();
-				getValues().add(val);
-				return val;
-			}
-			return super.next();
-		}
-
-		public synchronized IRepeatableIterator<T> getCopy() {
-			// If the current iterator still exists, we must exhaust it first
-			//
-			exhaustInnerIterator();
-			return super.getCopy();
-		}
-
-		public synchronized Object getIteratorProvider() {
-			exhaustInnerIterator();
-			return super.getIteratorProvider();
-		}
-
-		private void exhaustInnerIterator() {
-			if (innerIterator != null) {
-				List<T> values = getValues();
-				int savePos = values.size() - 1;
-				while (innerIterator.hasNext())
-					values.add(innerIterator.next());
-				innerIterator = null;
-				setPosition(savePos);
-			}
-		}
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/SingleVariableContext.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/SingleVariableContext.java
deleted file mode 100644
index 5d57b69c3..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/SingleVariableContext.java
+++ /dev/null
@@ -1,46 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql;
-
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-import org.eclipse.equinox.p2.ql.IExpression;
-
-public final class SingleVariableContext implements IEvaluationContext {
-	private final IEvaluationContext parentContext;
-
-	private Object value;
-
-	private final IExpression variable;
-
-	public SingleVariableContext(IEvaluationContext parentContext, IExpression variable) {
-		this.parentContext = parentContext;
-		this.variable = variable;
-	}
-
-	public Object getParameter(int position) {
-		return parentContext.getParameter(position);
-	}
-
-	public Object getParameter(String key) {
-		return parentContext.getParameter(key);
-	}
-
-	public Object getValue(IExpression var) {
-		return variable == var ? value : parentContext.getValue(var);
-	}
-
-	public void setValue(IExpression var, Object val) {
-		if (variable == var)
-			value = val;
-		else
-			parentContext.setValue(var, val);
-	}
-}
\ No newline at end of file
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/All.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/All.java
deleted file mode 100644
index a8181dc2c..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/All.java
+++ /dev/null
@@ -1,46 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import java.util.Iterator;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-
-/**
- * A collection filter that yields true if the <code>filter</code> yields true for
- * all of the elements of the <code>collection</code>
- */
-final class All extends CollectionFilter {
-	All(Expression collection, LambdaExpression lambda) {
-		super(collection, lambda);
-	}
-
-	public int getExpressionType() {
-		return TYPE_ALL;
-	}
-
-	Object evaluate(IEvaluationContext context, Iterator<?> itor) {
-		Variable variable = lambda.getItemVariable();
-		while (itor.hasNext()) {
-			variable.setValue(context, itor.next());
-			if (lambda.evaluate(context) != Boolean.TRUE)
-				return Boolean.FALSE;
-		}
-		return Boolean.TRUE;
-	}
-
-	String getOperator() {
-		return KEYWORD_ALL;
-	}
-
-	boolean isBoolean() {
-		return true;
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/And.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/And.java
deleted file mode 100644
index 992ad9be5..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/And.java
+++ /dev/null
@@ -1,73 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import java.util.*;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-
-/**
- * n-ary AND operator. This operator evaluates its first operand and then checks
- * the class of the result. If the class is {@link Boolean} then it is assumed
- * that all other operands also evaluates to a boolean and the full evaluation is
- * <code>true</code> if all its operands evaluate to <code>true</code>. If the first
- * result was not of class {@link Boolean}, then it is assumed that it can be accessed
- * as an {@link Iterator} and that all other operands also evaluates to something that
- * can be accessed as an {@link Iterator}. The AND operator will then function as a
- * INTERSECT operator and the result is the set of elements that were found in all operands. 
- */
-final class And extends NAry {
-	And(Expression[] operands) {
-		super(assertLength(operands, 2, OPERATOR_AND));
-	}
-
-	public Object evaluate(IEvaluationContext context) {
-		Object firstValue = operands[0].evaluate(context);
-
-		// Determine operation mode
-		if (firstValue instanceof Boolean) {
-			// The first value was boolean. Assume that the rest are too
-			if (!((Boolean) firstValue).booleanValue())
-				return Boolean.FALSE;
-
-			for (int idx = 1; idx < operands.length; ++idx) {
-				if (operands[idx].evaluate(context) != Boolean.TRUE)
-					return Boolean.FALSE;
-			}
-			return Boolean.TRUE;
-		}
-
-		// Not a boolean. Assume that we can use an iterator on all values
-		Set<?> resultSet = asSet(firstValue, false); // Safe since it will not be modified
-		for (int idx = 1; idx < operands.length && !resultSet.isEmpty(); ++idx) {
-			Iterator<?> itor = operands[idx].evaluateAsIterator(context);
-			Set<Object> retained = new HashSet<Object>();
-			while (itor.hasNext()) {
-				Object value = itor.next();
-				if (resultSet.contains(value))
-					retained.add(value);
-			}
-			resultSet = retained;
-		}
-		return resultSet;
-	}
-
-	public int getExpressionType() {
-		return TYPE_AND;
-	}
-
-	String getOperator() {
-		return OPERATOR_AND;
-	}
-
-	int getPriority() {
-		return PRIORITY_AND;
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Array.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Array.java
index ebba0e5ca..62dfb329c 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Array.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Array.java
@@ -12,13 +12,14 @@ package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.Iterator;
 import java.util.NoSuchElementException;
-import org.eclipse.equinox.internal.p2.ql.parser.IParserConstants;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * An array of expressions
  */
-final class Array extends NAry {
+final class Array extends NAry implements IQLConstants, IQLExpression {
 	final class ArrayIterator implements Iterator<Object> {
 		private final IEvaluationContext context;
 
@@ -45,19 +46,8 @@ final class Array extends NAry {
 		}
 	}
 
-	static void elementsToString(StringBuffer bld, Expression[] elements) {
-		int top = elements.length;
-		if (top > 0) {
-			elements[0].toString(bld);
-			for (int idx = 1; idx < top; ++idx) {
-				bld.append(", "); //$NON-NLS-1$
-				appendOperand(bld, elements[idx], PRIORITY_COMMA);
-			}
-		}
-	}
-
 	Array(Expression[] operands) {
-		super(assertLength(operands, 0, IParserConstants.OPERATOR_ARRAY));
+		super(assertLength(operands, 0, OPERATOR_ARRAY));
 	}
 
 	public Object evaluate(IEvaluationContext context) {
@@ -72,29 +62,17 @@ final class Array extends NAry {
 		return TYPE_ARRAY;
 	}
 
-	public void toString(StringBuffer bld) {
+	public void toString(StringBuffer bld, Variable rootVariable) {
 		bld.append('[');
-		elementsToString(bld, operands);
+		elementsToString(bld, rootVariable, operands);
 		bld.append(']');
 	}
 
-	String getOperator() {
-		return IParserConstants.OPERATOR_ARRAY;
-	}
-
-	int getPriority() {
-		return PRIORITY_CONSTRUCTOR;
-	}
-
-	boolean isBoolean() {
-		return false;
-	}
-
-	boolean isCollection() {
-		return true;
+	public String getOperator() {
+		return OPERATOR_ARRAY;
 	}
 
-	boolean isElementBoolean() {
-		return super.isBoolean();
+	public int getPriority() {
+		return PRIORITY_FUNCTION;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Assignment.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Assignment.java
index 23b69e8a7..22b747b7e 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Assignment.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Assignment.java
@@ -10,12 +10,15 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import java.util.Iterator;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * An expression representing a variable stack in the current thread.
  */
-class Assignment extends Binary {
+class Assignment extends Binary implements IQLConstants, IQLExpression {
 	Assignment(Variable variable, Expression expression) {
 		super(variable, expression);
 	}
@@ -30,19 +33,17 @@ class Assignment extends Binary {
 		return TYPE_ASSIGNMENT;
 	}
 
-	int getPriority() {
-		return PRIORITY_ASSIGNMENT;
+	public int getPriority() {
+		return IExpressionConstants.PRIORITY_ASSIGNMENT;
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return OPERATOR_ASSIGN;
 	}
 
-	boolean isBoolean() {
-		return rhs.isBoolean();
-	}
-
-	boolean isCollection() {
-		return rhs.isCollection();
+	public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
+		Iterator<?> value = rhs.evaluateAsIterator(context);
+		context.setValue(lhs, value);
+		return value;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/At.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/At.java
index 70b97119f..70d1639f9 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/At.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/At.java
@@ -10,76 +10,30 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
-import java.util.*;
-import org.eclipse.equinox.internal.p2.ql.expression.Member.DynamicMember;
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
+import org.eclipse.equinox.internal.p2.metadata.expression.Member;
 import org.eclipse.equinox.p2.metadata.IInstallableUnit;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 import org.eclipse.equinox.p2.ql.ITranslationSupport;
 
 /**
  * This class represents indexed or keyed access to an indexed collection
  * or a map.
  */
-final class At extends Binary {
+final class At extends org.eclipse.equinox.internal.p2.metadata.expression.At implements IQLExpression {
 	At(Expression lhs, Expression rhs) {
 		super(lhs, rhs);
 	}
 
-	public Object evaluate(IEvaluationContext context) {
-		Object lval;
-		if (lhs instanceof DynamicMember) {
-			DynamicMember lm = (DynamicMember) lhs;
-			Object instance = lm.operand.evaluate(context);
-			if (instance instanceof IInstallableUnit) {
-				if ("properties".equals(lm.name)) //$NON-NLS-1$
-					// Avoid full copy of the properties map just to get one member
-					return ((IInstallableUnit) instance).getProperty((String) rhs.evaluate(context));
-
-				if (VARIABLE_TRANSLATIONS.equals(lm.name)) {
-					ITranslationSupport ts = (ITranslationSupport) Variable.TRANSLATIONS.evaluate(context);
-					return ts.getIUProperty((IInstallableUnit) instance, (String) rhs.evaluate(context));
-				}
+	protected Object handleMember(IEvaluationContext context, Member member, Object instance, boolean[] handled) {
+		if (instance instanceof IInstallableUnit) {
+			if (IQLConstants.VARIABLE_TRANSLATIONS.equals(member.getName())) {
+				ITranslationSupport ts = (ITranslationSupport) QLFactory.TRANSLATIONS.evaluate(context);
+				handled[0] = true;
+				return ts.getIUProperty((IInstallableUnit) instance, (String) rhs.evaluate(context));
 			}
-			lval = lm.invoke(instance);
-		} else
-			lval = lhs.evaluate(context);
-
-		Object rval = rhs.evaluate(context);
-		if (lval == null)
-			throw new IllegalArgumentException("Unable to use [] on null"); //$NON-NLS-1$
-
-		if (lval instanceof Map<?, ?>)
-			return ((Map<?, ?>) lval).get(rval);
-
-		if (rval instanceof Number) {
-			if (lval instanceof List<?>)
-				return ((List<?>) lval).get(((Number) rval).intValue());
-			if (lval != null && lval.getClass().isArray())
-				return ((Object[]) lval)[((Number) rval).intValue()];
 		}
-
-		if (lval instanceof Dictionary<?, ?>)
-			return ((Dictionary<?, ?>) lval).get(rval);
-
-		throw new IllegalArgumentException("Unable to use [] on a " + lval.getClass().getName()); //$NON-NLS-1$
-	}
-
-	public int getExpressionType() {
-		return TYPE_AT;
-	}
-
-	public void toString(StringBuffer bld) {
-		appendOperand(bld, lhs, getPriority());
-		bld.append('[');
-		appendOperand(bld, rhs, PRIORITY_COMMA);
-		bld.append(']');
-	}
-
-	String getOperator() {
-		return OPERATOR_AT;
-	}
-
-	int getPriority() {
-		return PRIORITY_MEMBER;
+		return super.handleMember(context, member, instance, handled);
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Binary.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Binary.java
deleted file mode 100644
index ac17e0d49..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Binary.java
+++ /dev/null
@@ -1,47 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import org.eclipse.equinox.p2.ql.IExpressionVisitor;
-
-/**
- * The abstract base class for all binary operations
- */
-abstract class Binary extends Expression {
-	final Expression lhs;
-
-	final Expression rhs;
-
-	Binary(Expression lhs, Expression rhs) {
-		this.lhs = lhs;
-		this.rhs = rhs;
-	}
-
-	public boolean accept(IExpressionVisitor visitor) {
-		return super.accept(visitor) && lhs.accept(visitor) && rhs.accept(visitor);
-	}
-
-	public void toString(StringBuffer bld) {
-		appendOperand(bld, lhs, getPriority());
-		bld.append(' ');
-		bld.append(getOperator());
-		bld.append(' ');
-		appendOperand(bld, rhs, getPriority());
-	}
-
-	int countReferenceToEverything() {
-		return lhs.countReferenceToEverything() + rhs.countReferenceToEverything();
-	}
-
-	int getPriority() {
-		return PRIORITY_BINARY; // Default priority
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/BooleanFunction.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/BooleanFunction.java
index 10268eb36..860fe6e12 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/BooleanFunction.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/BooleanFunction.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
+ * Copyright (c) 2010 Cloudsmith Inc. and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -10,14 +10,15 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
+
 /**
  * A function that obtains a class based on a String
  */
-final class BooleanFunction extends Function {
+public final class BooleanFunction extends Function {
 
 	public BooleanFunction(Expression[] operands) {
 		super(assertLength(operands, 1, 1, KEYWORD_BOOLEAN));
-		assertNotCollection(operands[0], "parameter"); //$NON-NLS-1$
 	}
 
 	boolean assertSingleArgumentClass(Object v) {
@@ -32,7 +33,7 @@ final class BooleanFunction extends Function {
 		return Boolean.FALSE;
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_BOOLEAN;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/CapabilityIndexFunction.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/CapabilityIndexFunction.java
index 99e37e985..56297974e 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/CapabilityIndexFunction.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/CapabilityIndexFunction.java
@@ -11,26 +11,75 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.Iterator;
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
+import org.eclipse.equinox.internal.p2.metadata.expression.Member;
 import org.eclipse.equinox.internal.p2.ql.CapabilityIndex;
 import org.eclipse.equinox.p2.metadata.IInstallableUnit;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.p2.metadata.IRequirement;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.ICapabilityIndex;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * A function that creates a {@link CapabilityIndex} based on a collection of
  * {@link IInstallableUnit} instances.
  */
-final class CapabilityIndexFunction extends Function {
+public final class CapabilityIndexFunction extends Function implements IQLConstants {
+	static abstract class CapabilityIndexMethod extends Member implements IQLExpression {
+		public CapabilityIndexMethod(Expression operand, String name, Expression[] args) {
+			super(operand, name, args);
+		}
+
+		final ICapabilityIndex getSelf(IEvaluationContext context) {
+			Object self = operand.evaluate(context);
+			if (self instanceof ICapabilityIndex)
+				return (ICapabilityIndex) self;
+			throw new IllegalArgumentException("lhs of member expected to be an ICapabilityIndex implementation"); //$NON-NLS-1$
+		}
+
+		public final Object evaluate(IEvaluationContext context) {
+			return evaluateAsIterator(context);
+		}
+
+		boolean isCollection() {
+			return true;
+		}
+	}
+
+	static final class SatisfiesAny extends CapabilityIndexMethod {
+
+		public SatisfiesAny(Expression operand, Expression[] argExpressions) {
+			super(operand, KEYWORD_SATISFIES_ANY, assertLength(argExpressions, 1, 1, KEYWORD_SATISFIES_ANY));
+		}
+
+		@SuppressWarnings("unchecked")
+		public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
+			return getSelf(context).satisfiesAny((Iterator<IRequirement>) argExpressions[0].evaluateAsIterator(context));
+		}
+	}
+
+	static final class SatisfiesAll extends CapabilityIndexMethod {
+
+		public SatisfiesAll(Expression operand, Expression[] argExpressions) {
+			super(operand, KEYWORD_SATISFIES_ALL, assertLength(argExpressions, 1, 1, KEYWORD_SATISFIES_ALL));
+		}
+
+		@SuppressWarnings("unchecked")
+		public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
+			return getSelf(context).satisfiesAll((Iterator<IRequirement>) argExpressions[0].evaluateAsIterator(context));
+		}
+	}
 
 	public CapabilityIndexFunction(Expression[] operands) {
 		super(assertLength(operands, 1, 1, KEYWORD_CAPABILITY_INDEX));
-		assertNotBoolean(operands[0], "parameter"); //$NON-NLS-1$
 	}
 
+	@SuppressWarnings("unchecked")
 	public Object evaluate(IEvaluationContext context) {
 		return new CapabilityIndex((Iterator<IInstallableUnit>) operands[0].evaluateAsIterator(context));
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_CAPABILITY_INDEX;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/ClassFunction.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/ClassFunction.java
index 5fe40c0ac..53d0b3044 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/ClassFunction.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/ClassFunction.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
+ * Copyright (c) 2010 Cloudsmith Inc. and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -10,15 +10,15 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
+
 /**
  * A function that obtains a class based on a String
  */
-final class ClassFunction extends Function {
+public final class ClassFunction extends Function {
 
 	public ClassFunction(Expression[] operands) {
 		super(assertLength(operands, 1, 1, KEYWORD_CLASS));
-		assertNotBoolean(operands[0], "parameter"); //$NON-NLS-1$
-		assertNotCollection(operands[0], "parameter"); //$NON-NLS-1$
 	}
 
 	boolean assertSingleArgumentClass(Object v) {
@@ -33,7 +33,7 @@ final class ClassFunction extends Function {
 		}
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_CLASS;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Collect.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Collect.java
index fddda5dd5..5f3a67ebc 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Collect.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Collect.java
@@ -11,12 +11,14 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.Iterator;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-import org.eclipse.equinox.p2.ql.IExpression;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.metadata.expression.IExpression;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  */
-final class Collect extends CollectionFilter {
+final class Collect extends CollectionFilter implements IQLExpression {
 	final class CollectIterator implements Iterator<Object> {
 		private final IEvaluationContext context;
 
@@ -48,11 +50,11 @@ final class Collect extends CollectionFilter {
 		super(collection, lambda);
 	}
 
-	Object evaluate(IEvaluationContext context, Iterator<?> itor) {
+	public Object evaluate(IEvaluationContext context, Iterator<?> itor) {
 		return evaluateAsIterator(context, itor);
 	}
 
-	Iterator<?> evaluateAsIterator(IEvaluationContext context, Iterator<?> itor) {
+	public Iterator<?> evaluateAsIterator(IEvaluationContext context, Iterator<?> itor) {
 		return new CollectIterator(context, itor);
 	}
 
@@ -60,11 +62,7 @@ final class Collect extends CollectionFilter {
 		return TYPE_COLLECT;
 	}
 
-	String getOperator() {
-		return KEYWORD_COLLECT;
-	}
-
-	boolean isCollection() {
-		return true;
+	public String getOperator() {
+		return IQLConstants.KEYWORD_COLLECT;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/CollectionFilter.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/CollectionFilter.java
deleted file mode 100644
index b33b28aee..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/CollectionFilter.java
+++ /dev/null
@@ -1,73 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import java.util.Iterator;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-import org.eclipse.equinox.p2.ql.IExpressionVisitor;
-
-/**
- * Some kind of operation that is performed for each element of a collection. I.e.
- * <code>x.&lt;operation&gt;(y | &lt;expression&rt;)</code>
- */
-abstract class CollectionFilter extends Unary {
-	static void appendProlog(StringBuffer bld, Expression lhs, String operator) {
-		if (lhs != Variable.EVERYTHING && lhs != Variable.ITEM) {
-			appendOperand(bld, lhs, PRIORITY_COLLECTION);
-			bld.append('.');
-		}
-		bld.append(operator);
-		bld.append('(');
-	}
-
-	final LambdaExpression lambda;
-
-	CollectionFilter(Expression collection, LambdaExpression lambda) {
-		super(collection);
-		this.lambda = lambda;
-	}
-
-	public boolean accept(IExpressionVisitor visitor) {
-		return super.accept(visitor) && lambda.accept(visitor);
-	}
-
-	public final Object evaluate(IEvaluationContext context) {
-		Iterator<?> lval = operand.evaluateAsIterator(context);
-		context = lambda.prolog(context);
-		return evaluate(context, lval);
-	}
-
-	public final Iterator<?> evaluateAsIterator(IEvaluationContext context) {
-		Iterator<?> lval = operand.evaluateAsIterator(context);
-		context = lambda.prolog(context);
-		return evaluateAsIterator(context, lval);
-	}
-
-	public void toString(StringBuffer bld) {
-		appendProlog(bld, operand, getOperator());
-		appendOperand(bld, lambda, PRIORITY_LAMBDA);
-		bld.append(')');
-	}
-
-	int countReferenceToEverything() {
-		return super.countReferenceToEverything() + lambda.countReferenceToEverything();
-	}
-
-	abstract Object evaluate(final IEvaluationContext context, Iterator<?> iterator);
-
-	Iterator<?> evaluateAsIterator(IEvaluationContext context, Iterator<?> iterator) {
-		throw new UnsupportedOperationException();
-	}
-
-	int getPriority() {
-		return PRIORITY_COLLECTION;
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Compare.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Compare.java
deleted file mode 100644
index 89d21d02e..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Compare.java
+++ /dev/null
@@ -1,71 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import org.eclipse.equinox.p2.metadata.Version;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-
-/**
- * Comparisons for magnitude.
- */
-final class Compare extends Binary {
-	final boolean compareLess;
-	final boolean equalOK;
-
-	Compare(Expression lhs, Expression rhs, boolean compareLess, boolean equalOK) {
-		super(lhs, rhs);
-		this.compareLess = compareLess;
-		this.equalOK = equalOK;
-		assertNotCollection(lhs, "lhs"); //$NON-NLS-1$
-		assertNotCollection(rhs, "rhs"); //$NON-NLS-1$
-	}
-
-	public Object evaluate(IEvaluationContext context) {
-		Object lval = lhs.evaluate(context);
-		Object rval = rhs.evaluate(context);
-		if (lval == null || rval == null)
-			throw new IllegalArgumentException("Cannot compare null to anything"); //$NON-NLS-1$
-
-		try {
-
-			if (lval.getClass() != rval.getClass()) {
-				if (lval instanceof Version && rval instanceof String)
-					rval = Version.create((String) rval);
-				else if (rval instanceof Version && lval instanceof String)
-					lval = Version.create((String) lval);
-				else if (lval instanceof String)
-					rval = rval.toString();
-				else if (rval instanceof String)
-					lval = lval.toString();
-			}
-
-			if (lval instanceof Comparable) {
-				int cmpResult = ((Comparable) lval).compareTo(rval);
-				return Boolean.valueOf(cmpResult == 0 ? equalOK : (cmpResult < 0 ? compareLess : !compareLess));
-			}
-		} catch (Exception e) {
-			//
-		}
-		throw new IllegalArgumentException("Cannot compare a " + lval.getClass().getName() + " to a " + rval.getClass().getName()); //$NON-NLS-1$//$NON-NLS-2$
-	}
-
-	public int getExpressionType() {
-		return compareLess ? (equalOK ? TYPE_LESS_EQUAL : TYPE_LESS) : (equalOK ? TYPE_GREATER_EQUAL : TYPE_GREATER);
-	}
-
-	String getOperator() {
-		return compareLess ? (equalOK ? OPERATOR_LT_EQUAL : OPERATOR_LT) : (equalOK ? OPERATOR_GT_EQUAL : OPERATOR_GT);
-	}
-
-	boolean isBoolean() {
-		return true;
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Condition.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Condition.java
index 543294be4..9de25672c 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Condition.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Condition.java
@@ -10,49 +10,55 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import java.util.Iterator;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * Comparisons for magnitude.
  */
-final class Condition extends Binary {
+final class Condition extends Binary implements IQLConstants, IQLExpression {
 	final Expression ifFalse;
 
 	Condition(Expression test, Expression ifTrue, Expression ifFalse) {
 		super(test, ifTrue);
 		this.ifFalse = ifFalse;
-		assertNotCollection(test, "test"); //$NON-NLS-1$
+	}
+
+	public boolean equals(Object o) {
+		return super.equals(o) && ifFalse.equals(((Condition) o).ifFalse);
 	}
 
 	public Object evaluate(IEvaluationContext context) {
 		return lhs.evaluate(context) == Boolean.TRUE ? rhs.evaluate(context) : ifFalse.evaluate(context);
 	}
 
-	public int getExpressionType() {
-		return TYPE_CONDITION;
+	public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
+		return lhs.evaluate(context) == Boolean.TRUE ? rhs.evaluateAsIterator(context) : ifFalse.evaluateAsIterator(context);
+	}
+
+	public int hashCode() {
+		return super.hashCode() * 31 + ifFalse.hashCode();
 	}
 
-	public void toString(StringBuffer bld) {
-		super.toString(bld);
+	public void toString(StringBuffer bld, Variable rootVariable) {
+		super.toString(bld, rootVariable);
 		bld.append(' ');
 		bld.append(OPERATOR_ELSE);
 		bld.append(' ');
-		appendOperand(bld, ifFalse, getPriority());
+		appendOperand(bld, rootVariable, ifFalse, getPriority());
 	}
 
-	String getOperator() {
-		return OPERATOR_IF;
-	}
-
-	int getPriority() {
-		return PRIORITY_CONDITION;
+	public int getExpressionType() {
+		return TYPE_CONDITION;
 	}
 
-	boolean isBoolean() {
-		return rhs.isBoolean() && ifFalse.isBoolean();
+	public String getOperator() {
+		return OPERATOR_IF;
 	}
 
-	boolean isCollection() {
-		return rhs.isCollection() && ifFalse.isCollection();
+	public int getPriority() {
+		return IExpressionConstants.PRIORITY_CONDITION;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Constant.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Constant.java
deleted file mode 100644
index 797f04535..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Constant.java
+++ /dev/null
@@ -1,94 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import java.util.*;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-import org.eclipse.equinox.p2.ql.SimplePattern;
-import org.eclipse.equinox.p2.query.IQueryResult;
-
-/**
- * An expression that represents a constant value.
- */
-final class Constant extends Expression {
-	private final Object value;
-
-	static final Constant NULL_CONSTANT = new Constant(null);
-
-	static final Constant TRUE_CONSTANT = new Constant(Boolean.TRUE);
-
-	static final Constant FALSE_CONSTANT = new Constant(Boolean.FALSE);
-
-	static Constant create(Object value) {
-		if (value == null)
-			return NULL_CONSTANT;
-		if (value == Boolean.TRUE)
-			return TRUE_CONSTANT;
-		if (value == Boolean.FALSE)
-			return FALSE_CONSTANT;
-		return new Constant(value);
-	}
-
-	private Constant(Object value) {
-		this.value = value;
-	}
-
-	public Object evaluate(IEvaluationContext context) {
-		return value;
-	}
-
-	public int getExpressionType() {
-		return TYPE_LITERAL;
-	}
-
-	public void toString(StringBuffer bld) {
-		if (value == null)
-			bld.append("null"); //$NON-NLS-1$
-		else if (value instanceof String) {
-			String str = (String) value;
-			char sep = str.indexOf('\'') >= 0 ? '"' : '\'';
-			bld.append(sep);
-			bld.append(str);
-			bld.append(sep);
-		} else if (value instanceof SimplePattern) {
-			appendEscaped(bld, '/', value.toString());
-		} else
-			bld.append(value);
-	}
-
-	int getPriority() {
-		return PRIORITY_LITERAL;
-	}
-
-	private void appendEscaped(StringBuffer bld, char delimiter, String str) {
-		bld.append(delimiter);
-		int top = str.length();
-		for (int idx = 0; idx < top; ++idx) {
-			char c = str.charAt(idx);
-			if (c == delimiter)
-				bld.append('\\');
-			bld.append(c);
-		}
-		bld.append(delimiter);
-	}
-
-	boolean isBoolean() {
-		return value instanceof Boolean;
-	}
-
-	boolean isCollection() {
-		return value instanceof Collection<?> || value instanceof Map<?, ?> || value instanceof Iterator<?> || value instanceof IQueryResult<?> || value != null && value.getClass().isArray();
-	}
-
-	String getOperator() {
-		return "<literal>"; //$NON-NLS-1$
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/ContextExpression.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/ContextExpression.java
index 031eb5017..26cbce481 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/ContextExpression.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/ContextExpression.java
@@ -11,37 +11,49 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.Iterator;
-import org.eclipse.equinox.internal.p2.ql.*;
-import org.eclipse.equinox.p2.ql.*;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.internal.p2.ql.Everything;
+import org.eclipse.equinox.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.ql.IContextExpression;
+import org.eclipse.equinox.p2.ql.ITranslationSupport;
 
 /**
  * The context expression is the top expression in context queries. It introduces the
  * variable 'everything' and initialized it with the iterator that represents all
  * available items.
  */
-final class ContextExpression<T> extends Unary implements IContextExpression<T> {
-
+public final class ContextExpression<T> extends Unary implements IContextExpression<T>, IQLConstants {
+	private static final Object[] noParams = new Object[0];
 	private final Class<T> elementClass;
+	private final Object[] parameters;
 
-	ContextExpression(Class<T> elementClass, Expression expression) {
+	public ContextExpression(Class<T> elementClass, Expression expression, Object[] parameters) {
 		super(expression);
 		this.elementClass = elementClass;
+		this.parameters = parameters == null ? noParams : parameters;
 	}
 
-	public void toString(StringBuffer bld) {
-		operand.toString(bld);
+	public boolean accept(IExpressionVisitor visitor) {
+		return visitor.visit(operand);
+	}
+
+	public void toString(StringBuffer bld, Variable rootVariable) {
+		operand.toString(bld, rootVariable);
 	}
 
-	public IEvaluationContext createContext(Iterator<T> iterator, Object[] params) {
-		IEvaluationContext context = new SingleVariableContext(new ParameterContext(params), Variable.EVERYTHING);
-		context.setValue(Variable.EVERYTHING, new Everything<T>(elementClass, iterator, operand.needsRepeatedIterations()));
+	public IEvaluationContext createContext(Iterator<T> iterator) {
+		Variable everything = QLFactory.EVERYTHING;
+		IEvaluationContext context = EvaluationContext.create(parameters, everything);
+		context.setValue(everything, new Everything<T>(elementClass, iterator, QLUtil.needsRepeadedAccessToEverything(operand)));
 		return context;
 	}
 
-	public IEvaluationContext createContext(Iterator<T> iterator, Object[] params, ITranslationSupport ts) {
-		IEvaluationContext context = new MultiVariableContext(new ParameterContext(params), new IExpression[] {Variable.EVERYTHING, Variable.TRANSLATIONS});
-		context.setValue(Variable.EVERYTHING, new Everything<T>(elementClass, iterator, operand.needsRepeatedIterations()));
-		context.setValue(Variable.TRANSLATIONS, ts);
+	public IEvaluationContext createContext(Iterator<T> iterator, ITranslationSupport ts) {
+		Variable everything = QLFactory.EVERYTHING;
+		IExpression translations = QLFactory.TRANSLATIONS;
+		IEvaluationContext context = EvaluationContext.create(parameters, new IExpression[] {everything, translations});
+		context.setValue(everything, new Everything<T>(elementClass, iterator, QLUtil.needsRepeadedAccessToEverything(operand)));
+		context.setValue(translations, ts);
 		return context;
 	}
 
@@ -50,26 +62,31 @@ final class ContextExpression<T> extends Unary implements IContextExpression<T>
 	}
 
 	public int getExpressionType() {
-		return operand.getExpressionType();
+		return 0;
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		throw new UnsupportedOperationException();
 	}
 
-	int getPriority() {
+	public int getPriority() {
 		return operand.getPriority();
 	}
 
-	Expression pipeFrom(Expression expr) {
-		return new ContextExpression<T>(elementClass, operand.pipeFrom(expr));
+	public Object[] getParameters() {
+		return parameters;
 	}
 
-	boolean isBoolean() {
-		return operand.isBoolean();
+	public int hashCode() {
+		return operand.hashCode();
 	}
 
-	boolean isCollection() {
-		return operand.isCollection();
+	@SuppressWarnings("unchecked")
+	public Iterator<T> iterator(IEvaluationContext context) {
+		return (Iterator<T>) evaluateAsIterator(context);
+	}
+
+	public void toString(StringBuffer bld) {
+		toString(bld, QLFactory.EVERYTHING);
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/LambdaExpression.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/CurryedLambdaExpression.java
index cdc1d7216..dfdeb7b76 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/LambdaExpression.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/CurryedLambdaExpression.java
@@ -10,31 +10,25 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
-import org.eclipse.equinox.internal.p2.ql.MultiVariableContext;
-import org.eclipse.equinox.internal.p2.ql.SingleVariableContext;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-import org.eclipse.equinox.p2.ql.IExpressionVisitor;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.metadata.expression.IExpressionVisitor;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * A function that executes some code
  */
-final class LambdaExpression extends Unary {
+final class CurryedLambdaExpression extends LambdaExpression implements IQLConstants, IQLExpression {
 	private static final Assignment[] emptyAssignmentArray = new Assignment[0];
 	private final Assignment[] assignments;
-	private final Variable each;
 
-	LambdaExpression(Variable each, Expression body, Assignment[] assignments) {
-		super(body);
-		this.each = each;
+	CurryedLambdaExpression(Variable each, Assignment[] assignments, Expression body) {
+		super(each, body);
 		if (assignments == null)
 			assignments = emptyAssignmentArray;
 		this.assignments = assignments;
 	}
 
-	LambdaExpression(Variable variable, Expression body) {
-		this(variable, body, null);
-	}
-
 	public boolean accept(IExpressionVisitor visitor) {
 		if (super.accept(visitor) && each.accept(visitor)) {
 			for (int idx = 0; idx < assignments.length; ++idx)
@@ -45,73 +39,53 @@ final class LambdaExpression extends Unary {
 		return false;
 	}
 
-	public int getExpressionType() {
-		return TYPE_LAMBDA;
+	public int compareTo(Expression e) {
+		int cmp = super.compareTo(e);
+		if (cmp == 0)
+			cmp = compare(assignments, ((CurryedLambdaExpression) e).assignments);
+		return cmp;
 	}
 
-	public void toString(StringBuffer bld) {
+	public boolean equals(Object o) {
+		return super.equals(o) && equals(assignments, ((CurryedLambdaExpression) o).assignments);
+	}
+
+	public int hashCode() {
+		return 31 * super.hashCode() + hashCode(assignments);
+	}
+
+	public void toString(StringBuffer bld, Variable rootVariable) {
 		int top = assignments.length;
 		if (top > 0) {
 			for (int idx = 0; idx < top; ++idx) {
-				appendOperand(bld, assignments[idx].rhs, PRIORITY_COMMA);
+				appendOperand(bld, rootVariable, assignments[idx].rhs, IExpressionConstants.PRIORITY_COMMA);
 				bld.append(", "); //$NON-NLS-1$
 			}
-			bld.append(OPERATOR_EACH);
+			bld.append(IQLConstants.OPERATOR_EACH);
 			bld.append(", {"); //$NON-NLS-1$
 			for (int idx = 0; idx < top; ++idx) {
-				appendOperand(bld, assignments[idx].lhs, PRIORITY_COMMA);
+				appendOperand(bld, rootVariable, assignments[idx].lhs, IExpressionConstants.PRIORITY_COMMA);
 				bld.append(", "); //$NON-NLS-1$
 			}
 		}
-		each.toString(bld);
-		bld.append(" | "); //$NON-NLS-1$
-		appendOperand(bld, operand, PRIORITY_COMMA);
+		super.toString(bld, rootVariable);
 		if (top > 0)
 			bld.append('}');
 	}
 
-	int countReferenceToEverything() {
-		if (super.countReferenceToEverything() > 0)
-			return 2;
-		for (int idx = 0; idx < assignments.length; ++idx)
-			if (assignments[idx].countReferenceToEverything() > 0)
-				return 2;
-		return 0;
-	}
-
-	Variable getItemVariable() {
-		return each;
-	}
-
-	String getOperator() {
-		return "|"; //$NON-NLS-1$
-	}
-
-	int getPriority() {
-		return PRIORITY_LAMBDA;
-	}
-
-	boolean isBoolean() {
-		return operand.isBoolean();
-	}
-
-	boolean isCollection() {
-		return operand.isCollection();
-	}
-
-	IEvaluationContext prolog(IEvaluationContext context) {
-		IEvaluationContext lambdaContext = new SingleVariableContext(context, each);
+	public IEvaluationContext prolog(IEvaluationContext context) {
+		IEvaluationContext lambdaContext = super.prolog(context);
 		int top = assignments.length;
 		if (top > 0) {
 			if (top == 1) {
 				Assignment v = assignments[0];
-				lambdaContext = new SingleVariableContext(lambdaContext, v.lhs);
+				lambdaContext = EvaluationContext.create(lambdaContext, v.lhs);
 				lambdaContext.setValue(v.lhs, v.rhs.evaluate(context));
 			} else {
 				Variable[] vars = new Variable[top];
 				for (int idx = 0; idx < top; ++idx)
 					vars[idx] = (Variable) assignments[idx].lhs;
-				lambdaContext = new MultiVariableContext(lambdaContext, vars);
+				lambdaContext = EvaluationContext.create(lambdaContext, vars);
 				for (int idx = 0; idx < top; ++idx)
 					lambdaContext.setValue(vars[idx], assignments[idx].rhs.evaluate(context));
 			}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Equals.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Equals.java
deleted file mode 100644
index 773fb75b4..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Equals.java
+++ /dev/null
@@ -1,60 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-
-/**
- * An expression that performs the == and != comparisons
- */
-final class Equals extends Binary {
-	final boolean negate;
-
-	Equals(Expression lhs, Expression rhs, boolean negate) {
-		super(lhs, rhs);
-		this.negate = negate;
-		assertNotCollection(lhs, "lhs"); //$NON-NLS-1$
-		assertNotCollection(rhs, "rhs"); //$NON-NLS-1$
-	}
-
-	public Object evaluate(IEvaluationContext context) {
-		Object lval = lhs.evaluate(context);
-		Object rval = rhs.evaluate(context);
-		boolean result;
-		if (lval == null || rval == null)
-			result = lval == rval;
-		else {
-			if (lval.getClass() != rval.getClass()) {
-				if (lval instanceof String)
-					rval = rval.toString();
-				else if (rval instanceof String)
-					lval = lval.toString();
-			}
-			result = lval.equals(rval);
-		}
-		if (negate)
-			result = !result;
-		return Boolean.valueOf(result);
-	}
-
-	public int getExpressionType() {
-		return negate ? TYPE_NOT_EQUALS : TYPE_EQUALS;
-	}
-
-	String getOperator() {
-		return negate ? OPERATOR_NOT_EQUALS : OPERATOR_EQUALS;
-	}
-
-	boolean isBoolean() {
-		return true;
-	}
-
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Exists.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Exists.java
deleted file mode 100644
index 71e967aec..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Exists.java
+++ /dev/null
@@ -1,46 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import java.util.Iterator;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-
-/**
- * A collection filter that yields true if the <code>filter</code> yields true for
- * any of the elements of the <code>collection</code>
- */
-final class Exists extends CollectionFilter {
-	Exists(Expression collection, LambdaExpression lambda) {
-		super(collection, lambda);
-	}
-
-	public int getExpressionType() {
-		return TYPE_EXISTS;
-	}
-
-	Object evaluate(IEvaluationContext context, Iterator<?> itor) {
-		Variable variable = lambda.getItemVariable();
-		while (itor.hasNext()) {
-			variable.setValue(context, itor.next());
-			if (lambda.evaluate(context) == Boolean.TRUE)
-				return Boolean.TRUE;
-		}
-		return Boolean.FALSE;
-	}
-
-	String getOperator() {
-		return KEYWORD_EXISTS;
-	}
-
-	boolean isBoolean() {
-		return true;
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Expression.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Expression.java
deleted file mode 100644
index fcace814a..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Expression.java
+++ /dev/null
@@ -1,174 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import java.util.*;
-import org.eclipse.equinox.internal.p2.ql.IRepeatableIterator;
-import org.eclipse.equinox.internal.p2.ql.RepeatableIterator;
-import org.eclipse.equinox.internal.p2.ql.parser.IParserConstants;
-import org.eclipse.equinox.p2.ql.*;
-import org.eclipse.equinox.p2.query.IQueryResult;
-
-/**
- * The base class of the expression tree.
- */
-abstract class Expression implements IExpression, IParserConstants {
-
-	static final Expression[] emptyArray = new Expression[0];
-
-	static Set<?> asSet(Object val, boolean forcePrivateCopy) {
-		if (val == null)
-			throw new IllegalArgumentException("Cannot convert null into an set"); //$NON-NLS-1$
-
-		if (val instanceof IRepeatableIterator<?>) {
-			Object provider = ((IRepeatableIterator<?>) val).getIteratorProvider();
-			if (!forcePrivateCopy) {
-				if (provider instanceof Set<?>)
-					return (Set<?>) provider;
-				if (provider instanceof IQueryResult<?>)
-					return ((IQueryResult<?>) provider).unmodifiableSet();
-			}
-
-			if (provider instanceof Collection<?>)
-				val = provider;
-		} else {
-			if (!forcePrivateCopy) {
-				if (val instanceof Set<?>)
-					return (Set<?>) val;
-				if (val instanceof IQueryResult<?>)
-					return ((IQueryResult<?>) val).unmodifiableSet();
-			}
-		}
-
-		HashSet<Object> result;
-		if (val instanceof Collection<?>)
-			result = new HashSet<Object>((Collection<?>) val);
-		else {
-			result = new HashSet<Object>();
-			Iterator<?> iterator = RepeatableIterator.create(val);
-			while (iterator.hasNext())
-				result.add(iterator.next());
-		}
-		return result;
-	}
-
-	/**
-	 * Let the visitor visit this instance and all expressions that this
-	 * instance contains.
-	 * @param visitor The visiting visitor.
-	 * @return <code>true</code> if the visitor should continue visiting, <code>false</code> otherwise.
-	 */
-	public boolean accept(IExpressionVisitor visitor) {
-		return visitor.accept(this);
-	}
-
-	/**
-	 * Evaluate this expression with given context and variables.
-	 * @param context The evaluation context
-	 * @return The result of the evaluation.
-	 */
-	public abstract Object evaluate(IEvaluationContext context);
-
-	public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
-		Object value = evaluate(context);
-		if (!(value instanceof Iterator<?>))
-			value = RepeatableIterator.create(value);
-		return (Iterator<?>) value;
-	}
-
-	/**
-	 * Checks if the expression will make repeated requests for the 'everything' iterator.
-	 * @return <code>true</code> if repeated requests will be made, <code>false</code> if not.
-	 */
-	public boolean needsRepeatedIterations() {
-		return countReferenceToEverything() > 1;
-	}
-
-	public final boolean needsTranslations() {
-		final boolean[] translationSupportNeeded = new boolean[] {false};
-		accept(new IExpressionVisitor() {
-			public boolean accept(IExpression expr) {
-				if (((Expression) expr).isReferencingTranslations()) {
-					translationSupportNeeded[0] = true;
-					return false;
-				}
-				return true;
-			}
-		});
-		return translationSupportNeeded[0];
-	}
-
-	public String toString() {
-		StringBuffer bld = new StringBuffer();
-		toString(bld);
-		return bld.toString();
-	}
-
-	public abstract void toString(StringBuffer bld);
-
-	static void appendOperand(StringBuffer bld, Expression operand, int priority) {
-		if (priority < operand.getPriority()) {
-			bld.append('(');
-			operand.toString(bld);
-			bld.append(')');
-		} else
-			operand.toString(bld);
-	}
-
-	void assertNotCollection(Expression expr, String usage) {
-		if (expr.isCollection())
-			throw new IllegalArgumentException("A collection cannot be used as " + usage + " in a " + getOperator()); //$NON-NLS-1$//$NON-NLS-2$
-	}
-
-	void assertNotBoolean(Expression expr, String usage) {
-		if (expr.isBoolean())
-			throw new IllegalArgumentException("A boolean cannot be used as " + usage + " in a " + getOperator()); //$NON-NLS-1$//$NON-NLS-2$
-	}
-
-	int countReferenceToEverything() {
-		return 0;
-	}
-
-	abstract String getOperator();
-
-	abstract int getPriority();
-
-	boolean isBoolean() {
-		return false;
-	}
-
-	boolean isCollection() {
-		return false;
-	}
-
-	boolean isElementBoolean() {
-		return false;
-	}
-
-	boolean isReferencingTranslations() {
-		return false;
-	}
-
-	boolean isPipeable() {
-		// TODO Auto-generated method stub
-		return false;
-	}
-
-	Expression pipeFrom(Expression nxt) {
-		// TODO Auto-generated method stub
-		return null;
-	}
-
-	boolean isElementCollection() {
-		// TODO Auto-generated method stub
-		return false;
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/FilterFunction.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/FilterFunction.java
index 5f0130c36..0a4f96995 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/FilterFunction.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/FilterFunction.java
@@ -10,34 +10,26 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
-import org.eclipse.equinox.internal.p2.metadata.LDAPQuery;
-import org.eclipse.equinox.internal.p2.ql.QLActivator;
-import org.osgi.framework.InvalidSyntaxException;
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
+import org.eclipse.equinox.p2.metadata.expression.ExpressionUtil;
 
 /**
  * A function that creates an OSGi filter based on a String
  */
-final class FilterFunction extends Function {
+public final class FilterFunction extends Function {
 	public FilterFunction(Expression[] operands) {
 		super(assertLength(operands, 1, 1, KEYWORD_FILTER));
-		assertNotBoolean(operands[0], "parameter"); //$NON-NLS-1$
-		assertNotCollection(operands[0], "parameter"); //$NON-NLS-1$
 	}
 
 	boolean assertSingleArgumentClass(Object v) {
-		return v instanceof LDAPQuery || v instanceof String;
+		return v instanceof String;
 	}
 
 	Object createInstance(Object arg) {
-		String str = (arg instanceof LDAPQuery) ? ((LDAPQuery) arg).getFilter() : (String) arg;
-		try {
-			return QLActivator.context.createFilter(str);
-		} catch (InvalidSyntaxException e) {
-			throw new IllegalArgumentException(e.getMessage());
-		}
+		return ExpressionUtil.parseLDAP((String) arg);
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_FILTER;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/First.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/First.java
index d587ab0bb..decd15906 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/First.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/First.java
@@ -11,22 +11,20 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.Iterator;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * A collection filter that yields the first element of the <code>collection</code> for which
  * the <code>filter</code> yields <code>true</code>
  */
-final class First extends CollectionFilter {
+final class First extends CollectionFilter implements IQLExpression {
 	First(Expression collection, LambdaExpression lambda) {
 		super(collection, lambda);
 	}
 
-	public int getExpressionType() {
-		return TYPE_FIRST;
-	}
-
-	Object evaluate(IEvaluationContext context, Iterator<?> itor) {
+	protected Object evaluate(IEvaluationContext context, Iterator<?> itor) {
 		Variable variable = lambda.getItemVariable();
 		while (itor.hasNext()) {
 			Object each = itor.next();
@@ -37,15 +35,11 @@ final class First extends CollectionFilter {
 		return null;
 	}
 
-	String getOperator() {
-		return KEYWORD_FIRST;
-	}
-
-	boolean isBoolean() {
-		return operand.isElementBoolean();
+	public int getExpressionType() {
+		return TYPE_FIRST;
 	}
 
-	boolean isCollection() {
-		return operand.isElementCollection();
+	public String getOperator() {
+		return IQLConstants.KEYWORD_FIRST;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Flatten.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Flatten.java
index bb94afcb7..b0ff4122c 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Flatten.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Flatten.java
@@ -11,8 +11,9 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.Iterator;
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
 import org.eclipse.equinox.internal.p2.ql.FlattenIterator;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
 
 /**
  * An expression that yields a new collection consisting of all elements of the
@@ -31,7 +32,7 @@ final class Flatten extends UnaryCollectionFilter {
 		return TYPE_FLATTEN;
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_FLATTEN;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Function.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Function.java
index 5497dca2b..d704681f2 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Function.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Function.java
@@ -10,19 +10,34 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import java.util.Iterator;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * An expression that represents a function such as filter(&lt;expr&gt;) or version(&lt;expr&gt;)
  */
-abstract class Function extends NAry {
+public abstract class Function extends NAry implements IQLExpression {
 
 	private Object instance;
 
-	Function(Expression[] operands) {
+	protected Function(Expression[] operands) {
 		super(operands);
 	}
 
+	boolean assertSingleArgumentClass(Object v) {
+		return true;
+	}
+
+	Object createInstance(Object arg) {
+		throw new UnsupportedOperationException();
+	}
+
+	final Object createInstance(String arg) {
+		throw new UnsupportedOperationException();
+	}
+
 	public Object evaluate(IEvaluationContext context) {
 		if (instance != null)
 			return instance;
@@ -31,7 +46,7 @@ abstract class Function extends NAry {
 		Object arg = operand.evaluate(context);
 		if (assertSingleArgumentClass(arg)) {
 			Object result = createInstance(arg);
-			if (operand instanceof Constant || operand instanceof Parameter)
+			if (operand instanceof Literal || operand instanceof Parameter)
 				// operand won't change over time so we can cache this instance.
 				instance = result;
 			return result;
@@ -40,38 +55,25 @@ abstract class Function extends NAry {
 		throw new IllegalArgumentException("Cannot create a " + getOperator() + " from " + what); //$NON-NLS-1$ //$NON-NLS-2$
 	}
 
-	boolean assertSingleArgumentClass(Object v) {
-		return true;
+	public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
+		Object value = evaluate(context);
+		if (!(value instanceof Iterator<?>))
+			value = RepeatableIterator.create(value);
+		return (Iterator<?>) value;
 	}
 
 	public int getExpressionType() {
 		return TYPE_FUNCTION;
 	}
 
-	public void toString(StringBuffer bld) {
+	public int getPriority() {
+		return PRIORITY_FUNCTION;
+	}
+
+	public void toString(StringBuffer bld, Variable rootVariable) {
 		bld.append(getOperator());
 		bld.append('(');
-		Array.elementsToString(bld, operands);
+		elementsToString(bld, rootVariable, operands);
 		bld.append(')');
 	}
-
-	final Object createInstance(String arg) {
-		throw new UnsupportedOperationException();
-	}
-
-	Object createInstance(Object arg) {
-		throw new UnsupportedOperationException();
-	}
-
-	int getPriority() {
-		return PRIORITY_CONSTRUCTOR;
-	}
-
-	boolean isBoolean() {
-		return false;
-	}
-
-	boolean isCollection() {
-		return false;
-	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/IQLConstants.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/IQLConstants.java
new file mode 100644
index 000000000..397cc13ed
--- /dev/null
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/IQLConstants.java
@@ -0,0 +1,30 @@
+package org.eclipse.equinox.internal.p2.ql.expression;
+
+public interface IQLConstants {
+	String KEYWORD_CAPABILITY_INDEX = "capabilityIndex"; //$NON-NLS-1$
+	String KEYWORD_COLLECT = "collect"; //$NON-NLS-1$
+	String KEYWORD_FIRST = "first"; //$NON-NLS-1$
+	String KEYWORD_FLATTEN = "flatten"; //$NON-NLS-1$
+	String KEYWORD_INTERSECT = "intersect"; //$NON-NLS-1$
+	String KEYWORD_IQUERY = "iquery"; //$NON-NLS-1$
+	String KEYWORD_LATEST = "latest"; //$NON-NLS-1$
+	String KEYWORD_LIMIT = "limit"; //$NON-NLS-1$
+	String KEYWORD_LOCALIZED_KEYS = "localizedKeys"; //$NON-NLS-1$
+	String KEYWORD_LOCALIZED_MAP = "localizedMap"; //$NON-NLS-1$
+	String KEYWORD_LOCALIZED_PROPERTY = "localizedProperty"; //$NON-NLS-1$
+	String KEYWORD_SATISFIES_ALL = "satisfiesAll"; //$NON-NLS-1$
+	String KEYWORD_SATISFIES_ANY = "satisfiesAny"; //$NON-NLS-1$
+	String KEYWORD_SELECT = "select"; //$NON-NLS-1$
+	String KEYWORD_SET = "set"; //$NON-NLS-1$
+	String KEYWORD_TRAVERSE = "traverse"; //$NON-NLS-1$
+	String KEYWORD_UNION = "union"; //$NON-NLS-1$
+	String KEYWORD_UNIQUE = "unique"; //$NON-NLS-1$
+
+	String VARIABLE_TRANSLATIONS = "translations"; //$NON-NLS-1$
+
+	String OPERATOR_ARRAY = "[]"; //$NON-NLS-1$
+	String OPERATOR_ASSIGN = "="; //$NON-NLS-1$
+	String OPERATOR_EACH = "_"; //$NON-NLS-1$
+	String OPERATOR_ELSE = ":"; //$NON-NLS-1$
+	String OPERATOR_IF = "?"; //$NON-NLS-1$
+}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Intersect.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Intersect.java
new file mode 100644
index 000000000..db6b81a5f
--- /dev/null
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Intersect.java
@@ -0,0 +1,53 @@
+/*******************************************************************************
+ * Copyright (c) 2009 Cloudsmith Inc. and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Cloudsmith Inc. - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.equinox.internal.p2.ql.expression;
+
+import java.util.*;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
+
+/**
+ * n-ary <code>intersect</code> operator. The result is the set of elements that were found in all operands. 
+ */
+final class Intersect extends Binary implements IQLConstants, IQLExpression {
+	Intersect(Expression operand, Expression param) {
+		super(operand, param);
+	}
+
+	public Object evaluate(IEvaluationContext context) {
+		return evaluateAsIterator(context);
+	}
+
+	public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
+		Set<?> resultSet = QLUtil.asSet(lhs.evaluate(context), false); // Safe since it will not be modified
+		Iterator<?> itor = rhs.evaluateAsIterator(context);
+		Set<Object> retained = new HashSet<Object>();
+		while (itor.hasNext()) {
+			Object value = itor.next();
+			if (resultSet.contains(value))
+				retained.add(value);
+		}
+		return RepeatableIterator.create(retained);
+	}
+
+	public int getExpressionType() {
+		return TYPE_INTERSECT;
+	}
+
+	public String getOperator() {
+		return KEYWORD_INTERSECT;
+	}
+
+	public int getPriority() {
+		return PRIORITY_COLLECTION;
+	}
+}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Latest.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Latest.java
index c1557298a..b5c6c720e 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Latest.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Latest.java
@@ -11,8 +11,9 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.*;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
 import org.eclipse.equinox.p2.metadata.IVersionedId;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
 
 /**
  * An expression that is especially targeted towards {@link IVersionedId} instances. It will
@@ -87,7 +88,7 @@ final class Latest extends UnaryCollectionFilter {
 		return TYPE_LATEST;
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_LATEST;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Limit.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Limit.java
index 926a073b4..10b8051d7 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Limit.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Limit.java
@@ -12,12 +12,14 @@ package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.Iterator;
 import java.util.NoSuchElementException;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * A collection filter that limits the number of entries in the collection
  */
-final class Limit extends Binary {
+final class Limit extends Binary implements IQLConstants, IQLExpression {
 
 	/**
 	 * An iterator that stops iterating after a given number of iterations.
@@ -50,15 +52,17 @@ final class Limit extends Binary {
 
 	Limit(Expression operand, Expression param) {
 		super(operand, param);
-		assertNotBoolean(operand, "operand"); //$NON-NLS-1$
-		assertNotCollection(param, "parameter"); //$NON-NLS-1$
 	}
 
 	Limit(Expression operand, int limit) {
-		this(operand, Constant.create(new Integer(limit)));
+		this(operand, (Expression) QLFactory.INSTANCE.constant(new Integer(limit)));
 	}
 
 	public Object evaluate(IEvaluationContext context) {
+		return evaluateAsIterator(context);
+	}
+
+	public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
 		Object rval = rhs.evaluate(context);
 		int limit = -1;
 		if (rval instanceof Integer)
@@ -72,25 +76,17 @@ final class Limit extends Binary {
 		return TYPE_LIMIT;
 	}
 
-	public void toString(StringBuffer bld) {
-		CollectionFilter.appendProlog(bld, lhs, getOperator());
-		appendOperand(bld, rhs, PRIORITY_COMMA);
+	public void toString(StringBuffer bld, Variable rootVariable) {
+		CollectionFilter.appendProlog(bld, rootVariable, lhs, getOperator());
+		appendOperand(bld, rootVariable, rhs, IExpressionConstants.PRIORITY_COMMA);
 		bld.append(')');
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_LIMIT;
 	}
 
-	int getPriority() {
+	public int getPriority() {
 		return PRIORITY_COLLECTION;
 	}
-
-	boolean isCollection() {
-		return true;
-	}
-
-	boolean isElementBoolean() {
-		return lhs.isElementBoolean();
-	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/MatchExpression.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/MatchExpression.java
deleted file mode 100644
index dadd153bb..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/MatchExpression.java
+++ /dev/null
@@ -1,64 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import org.eclipse.equinox.internal.p2.ql.*;
-import org.eclipse.equinox.p2.ql.*;
-
-/**
- * The match expression is the top expression in item queries. It introduces the
- * variable 'item' and initializes it with the item to match.
- */
-final class MatchExpression extends Unary implements IMatchExpression {
-
-	MatchExpression(Expression expression) {
-		super(expression);
-	}
-
-	public boolean isMatch(IEvaluationContext context, Object value) {
-		Variable.ITEM.setValue(context, value);
-		return operand.evaluate(context) == Boolean.TRUE;
-	}
-
-	public IEvaluationContext createContext(Object[] params) {
-		return new SingleVariableContext(new ParameterContext(params), Variable.ITEM);
-	}
-
-	public IEvaluationContext createContext(Object[] params, ITranslationSupport ts) {
-		IEvaluationContext context = new MultiVariableContext(new ParameterContext(params), new IExpression[] {Variable.ITEM, Variable.TRANSLATIONS});
-		context.setValue(Variable.TRANSLATIONS, ts);
-		return context;
-	}
-
-	public int getExpressionType() {
-		return operand.getExpressionType();
-	}
-
-	public void toString(StringBuffer bld) {
-		operand.toString(bld);
-	}
-
-	protected int getPriority() {
-		return operand.getPriority();
-	}
-
-	String getOperator() {
-		throw new UnsupportedOperationException();
-	}
-
-	Expression pipeFrom(Expression expr) {
-		return new MatchExpression(operand.pipeFrom(expr));
-	}
-
-	boolean isBoolean() {
-		return true;
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Matches.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Matches.java
index 6114347f4..eabf19fd7 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Matches.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Matches.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
+ * Copyright (c) 2010 Cloudsmith Inc. and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -11,9 +11,9 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.*;
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
+import org.eclipse.equinox.internal.p2.metadata.expression.LDAPApproximation;
 import org.eclipse.equinox.p2.metadata.*;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-import org.eclipse.equinox.p2.ql.SimplePattern;
 import org.osgi.framework.Filter;
 
 /**
@@ -22,74 +22,18 @@ import org.osgi.framework.Filter;
  * <p>The following things can be matched:</p>
  * <table border="1" cellpadding="3">
  * <tr><th>LHS</th><th>RHS</th><th>Implemented as</th></tr>
- * <tr><td>IProvidedCapability</td><td>IRequiredCapability</td><td>lhs.satisfies(rhs)</td></tr>
- * <tr><td>IInstallableUnit</td><td>IRequiredCapability</td><td>lhs.satisfies(rhs)</td></tr>
+ * <tr><td>IProvidedCapability</td><td>IRequirement</td><td>lhs.satisfies(rhs)</td></tr>
+ * <tr><td>IInstallableUnit</td><td>IRequirement</td><td>lhs.satisfies(rhs)</td></tr>
  * <tr><td>Version</td><td>VersionRange</td><td>rhs.isIncluded(lhs)</td></tr>
  * <tr><td>IInstallableUnit</td><td>Filter</td><td>rhs.matches(lhs.properties)</td></tr>
  * <tr><td>Map</td><td>Filter</td><td>rhs.match(lhs)</td></tr>
- * <tr><td>String</td><td>Pattern</td><td>rhs.matcher(lhs).matches()</td></tr>
- * <tr><td>&lt;any&gt;</td><td>Class</td><td>rhs.isInstance(lhs)</td></tr>
- * <tr><td>Class</td><td>Class</td><td>rhs.isAssignableFrom(lhs)</td></tr>
+ * <tr><td>{@link String}</td><td>{@link SimplePattern}</td><td>rhs.isMatch(lhs)</td></tr>
+ * <tr><td>{@link String}</td><td>{@link LDAPApproximation}</td><td>rhs.isMatch(lhs)</td></tr>
+ * <tr><td>&lt;any&gt;</td><td>{@link Class}</td><td>rhs.isInstance(lhs)</td></tr>
+ * <tr><td>{@link Class}</td><td>{@link Class}</td><td>rhs.isAssignableFrom(lhs)</td></tr>
  * </table>
  */
-final class Matches extends Binary {
-	Matches(Expression lhs, Expression rhs) {
-		super(lhs, rhs);
-		assertNotBoolean(lhs, "lhs"); //$NON-NLS-1$
-		assertNotBoolean(rhs, "rhs"); //$NON-NLS-1$
-		assertNotCollection(rhs, "rhs"); //$NON-NLS-1$
-	}
-
-	public Object evaluate(IEvaluationContext context) {
-		Object lval = lhs.evaluate(context);
-		Object rval = rhs.evaluate(context);
-
-		if (rval instanceof IRequirement) {
-			IRequirement requirement = (IRequirement) rval;
-			if (lval instanceof IInstallableUnit)
-				return Boolean.valueOf(((IInstallableUnit) lval).satisfies(requirement));
-			if (lval instanceof IProvidedCapability)
-				return Boolean.valueOf(((IProvidedCapability) lval).satisfies(requirement));
-
-		} else if (rval instanceof VersionRange) {
-			if (lval instanceof Version)
-				return Boolean.valueOf(((VersionRange) rval).isIncluded((Version) lval));
-
-		} else if (rval instanceof SimplePattern) {
-			if (lval instanceof CharSequence)
-				return Boolean.valueOf(((SimplePattern) rval).isMatch((CharSequence) lval));
-
-		} else if (rval instanceof IUpdateDescriptor) {
-			if (lval instanceof IInstallableUnit)
-				return Boolean.valueOf(((IUpdateDescriptor) rval).isUpdateOf((IInstallableUnit) lval));
-
-		} else if (rval instanceof Filter) {
-			if (lval instanceof IInstallableUnit)
-				return Boolean.valueOf(((Filter) rval).match(new Hashtable<String, String>(((IInstallableUnit) lval).getProperties())));
-			if (lval instanceof Dictionary<?, ?>)
-				return Boolean.valueOf(((Filter) rval).match((Dictionary<?, ?>) lval));
-			if (lval instanceof Map<?, ?>)
-				return Boolean.valueOf(((Filter) rval).match(new Hashtable<Object, Object>((Map<?, ?>) lval)));
-
-		} else if (rval instanceof Locale) {
-			if (lval instanceof String)
-				return Boolean.valueOf(matchLocaleVariants((Locale) rval, (String) lval));
-
-		} else if (rval instanceof Class<?>) {
-			Class<?> rclass = (Class<?>) rval;
-			return Boolean.valueOf(lval instanceof Class<?> ? rclass.isAssignableFrom((Class<?>) lval) : rclass.isInstance(lval));
-		}
-
-		if (lval == null || rval == null)
-			return Boolean.FALSE;
-
-		throw new IllegalArgumentException("Cannot match a " + lval.getClass().getName() + " with a " + rval.getClass().getName()); //$NON-NLS-1$//$NON-NLS-2$
-	}
-
-	public int getExpressionType() {
-		return TYPE_MATCHES;
-	}
-
+final class Matches extends org.eclipse.equinox.internal.p2.metadata.expression.Matches {
 	private static boolean equals(String a, String b, int startPos, int endPos) {
 		if (endPos - startPos != b.length())
 			return false;
@@ -118,11 +62,35 @@ final class Matches extends Binary {
 				: equals(lval, rval.getCountry(), countryStart, uscore) && equals(lval, rval.getVariant(), uscore + 1, lval.length());
 	}
 
-	String getOperator() {
-		return OPERATOR_MATCHES;
+	Matches(Expression lhs, Expression rhs) {
+		super(lhs, rhs);
 	}
 
-	boolean isBoolean() {
-		return true;
+	protected boolean match(Object lval, Object rval) {
+		if (rval instanceof IRequirement) {
+			IRequirement requirement = (IRequirement) rval;
+			if (lval instanceof IInstallableUnit)
+				return Boolean.valueOf(((IInstallableUnit) lval).satisfies(requirement));
+		} else if (rval instanceof VersionRange) {
+			if (lval instanceof Version)
+				return Boolean.valueOf(((VersionRange) rval).isIncluded((Version) lval));
+
+		} else if (rval instanceof IUpdateDescriptor) {
+			if (lval instanceof IInstallableUnit)
+				return Boolean.valueOf(((IUpdateDescriptor) rval).isUpdateOf((IInstallableUnit) lval));
+
+		} else if (rval instanceof Filter) {
+			if (lval instanceof IInstallableUnit)
+				return Boolean.valueOf(((Filter) rval).match(new Hashtable<String, String>(((IInstallableUnit) lval).getProperties())));
+			if (lval instanceof Dictionary<?, ?>)
+				return Boolean.valueOf(((Filter) rval).match((Dictionary<?, ?>) lval));
+			if (lval instanceof Map<?, ?>)
+				return Boolean.valueOf(((Filter) rval).match(new Hashtable<Object, Object>((Map<?, ?>) lval)));
+
+		} else if (rval instanceof Locale) {
+			if (lval instanceof String)
+				return Boolean.valueOf(matchLocaleVariants((Locale) rval, (String) lval));
+		}
+		return super.match(lval, rval);
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Member.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Member.java
deleted file mode 100644
index 21c99e40c..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Member.java
+++ /dev/null
@@ -1,197 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import java.lang.reflect.*;
-import java.util.Iterator;
-import org.eclipse.equinox.p2.metadata.IRequirement;
-import org.eclipse.equinox.p2.ql.*;
-
-/**
- * <p>An expression that performs member calls to obtain some value
- * from some object instance. It uses standard bean semantics so
- * that an attempt to obtain &quot;value&quot; will cause an
- * attempt to call <code>getValue()</code> and if no such method
- * exists, <code>isValue()</code> and if that doesn't work either,
- * <code>value()</code>.</p>
- */
-abstract class Member extends Unary {
-
-	static Member createDynamicMember(Expression operand, String name) {
-		return new DynamicMember(operand, name);
-	}
-
-	static final Object[] NO_ARGS = new Object[0];
-
-	final String name;
-	final Expression[] argExpressions;
-
-	static abstract class CapabilityIndexMethod extends Member {
-		public CapabilityIndexMethod(Expression operand, String name, Expression[] args) {
-			super(operand, name, args);
-		}
-
-		final ICapabilityIndex getSelf(IEvaluationContext context) {
-			Object self = operand.evaluate(context);
-			if (self instanceof ICapabilityIndex)
-				return (ICapabilityIndex) self;
-			throw new IllegalArgumentException("lhs of member expected to be an ICapabilityIndex implementation"); //$NON-NLS-1$
-		}
-
-		public final Object evaluate(IEvaluationContext context) {
-			return evaluateAsIterator(context);
-		}
-
-		boolean isCollection() {
-			return true;
-		}
-	}
-
-	static final class CapabilityIndex_satisfiesAny extends CapabilityIndexMethod {
-
-		public CapabilityIndex_satisfiesAny(Expression operand, Expression[] argExpressions) {
-			super(operand, KEYWORD_SATISFIES_ANY, NAry.assertLength(argExpressions, 1, 1, KEYWORD_SATISFIES_ANY));
-		}
-
-		@SuppressWarnings("unchecked")
-		public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
-			return getSelf(context).satisfiesAny((Iterator<IRequirement>) argExpressions[0].evaluateAsIterator(context));
-		}
-	}
-
-	static final class CapabilityIndex_satisfiesAll extends CapabilityIndexMethod {
-
-		public CapabilityIndex_satisfiesAll(Expression operand, Expression[] argExpressions) {
-			super(operand, KEYWORD_SATISFIES_ALL, NAry.assertLength(argExpressions, 1, 1, KEYWORD_SATISFIES_ALL));
-		}
-
-		@SuppressWarnings("unchecked")
-		public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
-			return getSelf(context).satisfiesAll((Iterator<IRequirement>) argExpressions[0].evaluateAsIterator(context));
-		}
-	}
-
-	public boolean accept(IExpressionVisitor visitor) {
-		if (super.accept(visitor))
-			for (int idx = 0; idx < argExpressions.length; ++idx)
-				if (!argExpressions[idx].accept(visitor))
-					return false;
-		return true;
-	}
-
-	Member(Expression operand, String name, Expression[] args) {
-		super(operand);
-		this.name = name;
-		this.argExpressions = args;
-	}
-
-	public int getExpressionType() {
-		return TYPE_MEMBER;
-	}
-
-	public void toString(StringBuffer bld) {
-		if (operand == Variable.ITEM || operand == Variable.EVERYTHING)
-			bld.append(name);
-		else {
-			appendOperand(bld, operand, getPriority());
-			bld.append('.');
-			bld.append(name);
-		}
-		if (argExpressions.length > 0) {
-			bld.append('(');
-			Array.elementsToString(bld, argExpressions);
-			bld.append(')');
-		}
-	}
-
-	String getOperator() {
-		return OPERATOR_MEMBER;
-	}
-
-	int getPriority() {
-		return PRIORITY_MEMBER;
-	}
-
-	static final class DynamicMember extends Member {
-		private static final Class<?>[] NO_ARG_TYPES = new Class[0];
-		private static final String GET_PREFIX = "get"; //$NON-NLS-1$
-		private static final String IS_PREFIX = "is"; //$NON-NLS-1$
-
-		DynamicMember(Expression operand, String name) {
-			super(operand, name, Expression.emptyArray);
-			if (!(name.startsWith(GET_PREFIX) || name.startsWith(IS_PREFIX)))
-				name = GET_PREFIX + Character.toUpperCase(name.charAt(0)) + name.substring(1);
-			this.methodName = name;
-		}
-
-		private Class<?> lastClass;
-		private Method method;
-		private String methodName;
-
-		public Object evaluate(IEvaluationContext context) {
-			return invoke(operand.evaluate(context));
-		}
-
-		boolean isReferencingTranslations() {
-			return VARIABLE_TRANSLATIONS.equals(name);
-		}
-
-		Object invoke(Object self) {
-			if (self == null)
-				throw new IllegalArgumentException("Cannot access member " + name + " in null"); //$NON-NLS-1$//$NON-NLS-2$
-
-			Class<?> c = self.getClass();
-			if (lastClass == null || !lastClass.isAssignableFrom(c)) {
-				Method m;
-				for (;;) {
-					try {
-						m = c.getMethod(methodName, NO_ARG_TYPES);
-						if (!Modifier.isPublic(m.getModifiers()))
-							throw new NoSuchMethodException();
-						break;
-					} catch (NoSuchMethodException e) {
-						if (methodName.startsWith(GET_PREFIX))
-							// Switch from using getXxx() to isXxx()
-							methodName = IS_PREFIX + Character.toUpperCase(name.charAt(0)) + name.substring(1);
-						else if (methodName.startsWith(IS_PREFIX))
-							// Switch from using isXxx() to xxx()
-							methodName = name;
-						else
-							throw new IllegalArgumentException("Cannot find a public member " + name + " in a " + self.getClass().getName()); //$NON-NLS-1$//$NON-NLS-2$
-					}
-				}
-
-				// Since we already checked that it's public. This will speed
-				// up the calls a bit.
-				m.setAccessible(true);
-				lastClass = c;
-				method = m;
-			}
-
-			Exception checked;
-			try {
-				return method.invoke(self, NO_ARGS);
-			} catch (IllegalArgumentException e) {
-				throw e;
-			} catch (IllegalAccessException e) {
-				checked = e;
-			} catch (InvocationTargetException e) {
-				Throwable cause = e.getTargetException();
-				if (cause instanceof RuntimeException)
-					throw (RuntimeException) cause;
-				if (cause instanceof Error)
-					throw (Error) cause;
-				checked = (Exception) cause;
-			}
-			throw new RuntimeException("Problem invoking " + methodName + " on a " + self.getClass().getName(), checked); //$NON-NLS-1$ //$NON-NLS-2$
-		}
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/NAry.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/NAry.java
deleted file mode 100644
index 22595deb7..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/NAry.java
+++ /dev/null
@@ -1,87 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import org.eclipse.equinox.p2.ql.IExpressionVisitor;
-
-/**
- * The abstract baseclass for all N-ary expressions
- *
- */
-abstract class NAry extends Expression {
-	static Expression[] assertLength(Expression[] operands, int length, String operand) {
-		if (operands == null)
-			operands = emptyArray;
-		if (operands.length < length)
-			throw new IllegalArgumentException("Not enough operands for " + operand); //$NON-NLS-1$
-		return operands;
-	}
-
-	static Expression[] assertLength(Expression[] operands, int minLength, int maxLength, String operand) {
-		if (operands == null)
-			operands = emptyArray;
-		if (operands.length < minLength)
-			throw new IllegalArgumentException("Not enough operands for " + operand); //$NON-NLS-1$
-		if (operands.length > maxLength)
-			throw new IllegalArgumentException("Too many operands for " + operand); //$NON-NLS-1$
-		return operands;
-	}
-
-	final Expression[] operands;
-
-	NAry(Expression[] operands) {
-		this.operands = operands;
-	}
-
-	public boolean accept(IExpressionVisitor visitor) {
-		if (super.accept(visitor))
-			for (int idx = 0; idx < operands.length; ++idx)
-				if (!operands[idx].accept(visitor))
-					return false;
-		return true;
-	}
-
-	public void toString(StringBuffer bld) {
-		appendOperand(bld, operands[0], getPriority());
-		for (int idx = 1; idx < operands.length; ++idx) {
-			bld.append(' ');
-			bld.append(getOperator());
-			bld.append(' ');
-			appendOperand(bld, operands[idx], getPriority());
-		}
-	}
-
-	int countReferenceToEverything() {
-		int count = 0;
-		for (int idx = 0; count < 2 && idx < operands.length; ++idx)
-			count += operands[idx].countReferenceToEverything();
-		return count;
-	}
-
-	abstract String getOperator();
-
-	boolean isBoolean() {
-		int idx = operands.length;
-		while (--idx >= 0)
-			if (!operands[idx].isBoolean())
-				return false;
-		return true;
-	}
-
-	boolean isCollection() {
-		int idx = operands.length;
-		while (--idx >= 0)
-			if (!operands[idx].isCollection())
-				return false;
-		return true;
-	}
-
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Not.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Not.java
deleted file mode 100644
index ab7b31f53..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Not.java
+++ /dev/null
@@ -1,42 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-
-/**
- * An expression that yields <code>true</code> when its operand does not.
- */
-final class Not extends Unary {
-	Not(Expression operand) {
-		super(operand);
-	}
-
-	public Object evaluate(IEvaluationContext context) {
-		return Boolean.valueOf(operand.evaluate(context) != Boolean.TRUE);
-	}
-
-	public int getExpressionType() {
-		return TYPE_NOT;
-	}
-
-	String getOperator() {
-		return OPERATOR_NOT;
-	}
-
-	int getPriority() {
-		return PRIORITY_NOT;
-	}
-
-	boolean isBoolean() {
-		return true;
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Or.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Or.java
deleted file mode 100644
index 4892782be..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Or.java
+++ /dev/null
@@ -1,71 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import java.util.Iterator;
-import java.util.Set;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-
-/**
- * n-ary OR operator. This operator evaluates its first operand and then checks
- * the class of the result. If the class is {@link Boolean} then it is assumed
- * that all other operands also evaluates to a boolean and the full evaluation is
- * <code>false</code> if none of its operands evaluate to <code>true</code>. If the
- * first result was not of class {@link Boolean}, then it is assumed that it can
- * be accessed as an {@link Iterator} and that all other operands also evaluates to
- * something that can be accessed an {@link Iterator}. The OR operator will then
- * function as a UNION operator and the result is the unique sum of all elements that
- * were found in all operands. 
- */
-final class Or extends NAry {
-	public Or(Expression[] operands) {
-		super(assertLength(operands, 2, OPERATOR_OR));
-	}
-
-	public Object evaluate(IEvaluationContext context) {
-		Object firstValue = operands[0].evaluate(context);
-
-		// Determine operation mode
-		if (firstValue instanceof Boolean) {
-			// The first value was boolean. Assume that the rest are too
-			if (((Boolean) firstValue).booleanValue())
-				return Boolean.TRUE;
-
-			for (int idx = 1; idx < operands.length; ++idx) {
-				if (operands[idx].evaluate(context) == Boolean.TRUE)
-					return Boolean.TRUE;
-			}
-			return Boolean.FALSE;
-		}
-
-		// Not a boolean. Assume that we can use an iterator on all values
-		@SuppressWarnings("unchecked")
-		Set<Object> resultSet = (Set<Object>) asSet(firstValue, true);
-		for (int idx = 1; idx < operands.length; ++idx) {
-			Iterator<?> itor = operands[idx].evaluateAsIterator(context);
-			while (itor.hasNext())
-				resultSet.add(itor.next());
-		}
-		return resultSet;
-	}
-
-	public int getExpressionType() {
-		return TYPE_OR;
-	}
-
-	String getOperator() {
-		return OPERATOR_OR;
-	}
-
-	int getPriority() {
-		return PRIORITY_OR;
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Parameter.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Parameter.java
deleted file mode 100644
index c6374ea2e..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Parameter.java
+++ /dev/null
@@ -1,64 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-
-/**
- * The abstract base class for the indexed and keyed parameters
- */
-abstract class Parameter extends Expression {
-	public int getExpressionType() {
-		return TYPE_PARAMETER;
-	}
-
-	int getPriority() {
-		return PRIORITY_PARAMETER;
-	}
-
-	String getOperator() {
-		return OPERATOR_PARAMETER;
-	}
-
-	static final class Indexed extends Parameter {
-		final int position;
-
-		Indexed(int position) {
-			this.position = position;
-		}
-
-		public Object evaluate(IEvaluationContext context) {
-			return context.getParameter(position);
-		}
-
-		public void toString(StringBuffer bld) {
-			bld.append('$');
-			bld.append(position);
-		}
-	}
-
-	static final class Keyed extends Parameter {
-		final String key;
-
-		public Keyed(String key) {
-			this.key = key;
-		}
-
-		public Object evaluate(IEvaluationContext context) {
-			return context.getParameter(key);
-		}
-
-		public void toString(StringBuffer bld) {
-			bld.append('$');
-			bld.append(key);
-		}
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/ExpressionFactory.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/QLFactory.java
index f603dd6e0..17bbb657a 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/ExpressionFactory.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/QLFactory.java
@@ -3,13 +3,20 @@ package org.eclipse.equinox.internal.p2.ql.expression;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
 import java.util.*;
-import org.eclipse.equinox.internal.p2.ql.parser.IParserConstants;
-import org.eclipse.equinox.p2.ql.*;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IExpression;
+import org.eclipse.equinox.p2.ql.IContextExpression;
+import org.eclipse.equinox.p2.ql.IQLFactory;
 
-public class ExpressionFactory implements IExpressionFactory, IParserConstants {
-	public static final IExpressionFactory INSTANCE = new ExpressionFactory();
+public class QLFactory extends ExpressionFactory implements IQLFactory, IQLConstants {
+	@SuppressWarnings("hiding")
+	public static final IQLFactory INSTANCE = new QLFactory();
 
-	private static final Map<String, Constructor<?>> functionMap;
+	public static final Variable EVERYTHING = new Variable(IExpressionConstants.VARIABLE_EVERYTHING);
+
+	public static final Variable TRANSLATIONS = new Variable(VARIABLE_TRANSLATIONS);
+
+	protected static final Map<String, Constructor<?>> functionMap;
 
 	static {
 		Class<?>[] args = new Class[] {Expression[].class};
@@ -19,8 +26,8 @@ public class ExpressionFactory implements IExpressionFactory, IParserConstants {
 			f.put(KEYWORD_FILTER, FilterFunction.class.getConstructor(args));
 			f.put(KEYWORD_VERSION, VersionFunction.class.getConstructor(args));
 			f.put(KEYWORD_RANGE, RangeFunction.class.getConstructor(args));
-			f.put(KEYWORD_SET, SetFunction.class.getConstructor(args));
 			f.put(KEYWORD_CLASS, ClassFunction.class.getConstructor(args));
+			f.put(KEYWORD_SET, SetFunction.class.getConstructor(args));
 			f.put(KEYWORD_IQUERY, WrappedIQuery.class.getConstructor(args));
 			f.put(KEYWORD_CAPABILITY_INDEX, CapabilityIndexFunction.class.getConstructor(args));
 			functionMap = Collections.unmodifiableMap(f);
@@ -29,22 +36,12 @@ public class ExpressionFactory implements IExpressionFactory, IParserConstants {
 		}
 	}
 
-	private static Expression[] convertArray(IExpression[] operands) {
-		Expression[] ops = new Expression[operands.length];
-		System.arraycopy(operands, 0, ops, 0, operands.length);
-		return ops;
-	}
-
-	private ExpressionFactory() {
-		// Maintain singleton
-	}
-
-	public IExpression all(IExpression collection, IExpression lambda) {
-		return new All((Expression) collection, (LambdaExpression) lambda);
+	public IExpression at(IExpression target, IExpression key) {
+		return new At((Expression) target, (Expression) key);
 	}
 
-	public IExpression and(IExpression[] operands) {
-		return new And(convertArray(operands));
+	public IExpression intersect(IExpression c1, IExpression c2) {
+		return new Intersect((Expression) c1, (Expression) c2);
 	}
 
 	public IExpression array(IExpression[] operands) {
@@ -55,10 +52,6 @@ public class ExpressionFactory implements IExpressionFactory, IParserConstants {
 		return new Assignment((Variable) variable, (Expression) expression);
 	}
 
-	public IExpression at(IExpression target, IExpression key) {
-		return new At((Expression) target, (Expression) key);
-	}
-
 	public IExpression collect(IExpression collection, IExpression lambda) {
 		return new Collect((Expression) collection, (LambdaExpression) lambda);
 	}
@@ -67,24 +60,8 @@ public class ExpressionFactory implements IExpressionFactory, IParserConstants {
 		return new Condition((Expression) test, (Expression) ifTrue, (Expression) ifFalse);
 	}
 
-	public IExpression constant(Object value) {
-		return Constant.create(value);
-	}
-
-	public <T> IContextExpression<T> contextExpression(Class<T> elementClass, IExpression expr) {
-		return new ContextExpression<T>(elementClass, (Expression) expr);
-	}
-
-	public IExpression dynamicMember(IExpression target, String name) {
-		return new Member.DynamicMember((Expression) target, name);
-	}
-
-	public IExpression equals(IExpression lhs, IExpression rhs) {
-		return new Equals((Expression) lhs, (Expression) rhs, false);
-	}
-
-	public IExpression exists(IExpression collection, IExpression lambda) {
-		return new Exists((Expression) collection, (LambdaExpression) lambda);
+	public <T> IContextExpression<T> contextExpression(Class<T> elementClass, IExpression expr, Object... parameters) {
+		return new ContextExpression<T>(elementClass, (Expression) expr, parameters);
 	}
 
 	public IExpression first(IExpression collection, IExpression lambda) {
@@ -95,7 +72,7 @@ public class ExpressionFactory implements IExpressionFactory, IParserConstants {
 		return new Flatten((Expression) collection);
 	}
 
-	public IExpression function(Object function, IExpression[] args) {
+	public IExpression function(Object function, IExpression... args) {
 		try {
 			return (IExpression) ((Constructor<?>) function).newInstance(new Object[] {convertArray(args)});
 		} catch (IllegalArgumentException e) {
@@ -116,36 +93,18 @@ public class ExpressionFactory implements IExpressionFactory, IParserConstants {
 		return functionMap;
 	}
 
-	public IExpression greater(IExpression lhs, IExpression rhs) {
-		return new Compare((Expression) lhs, (Expression) rhs, false, false);
-	}
-
-	public IExpression indexedParameter(int index) {
-		return new Parameter.Indexed(index);
-	}
-
-	public IExpression keyedParameter(String key) {
-		return new Parameter.Keyed(key);
-	}
-
-	public IExpression lambda(IExpression variable, IExpression body) {
-		return new LambdaExpression((Variable) variable, (Expression) body);
-	}
-
-	public IExpression lambda(IExpression variable, IExpression body, IExpression[] assignments) {
+	public IExpression lambda(IExpression variable, IExpression[] assignments, IExpression body) {
+		if (assignments.length == 0)
+			return super.lambda(variable, body);
 		Assignment[] asgns = new Assignment[assignments.length];
 		System.arraycopy(assignments, 0, asgns, 0, assignments.length);
-		return new LambdaExpression((Variable) variable, (Expression) body, asgns);
+		return new CurryedLambdaExpression((Variable) variable, asgns, (Expression) body);
 	}
 
 	public IExpression latest(IExpression collection) {
 		return new Latest((Expression) collection);
 	}
 
-	public IExpression less(IExpression lhs, IExpression rhs) {
-		return new Compare((Expression) lhs, (Expression) rhs, true, false);
-	}
-
 	public IExpression limit(IExpression collection, IExpression limit) {
 		return new Limit((Expression) collection, (Expression) limit);
 	}
@@ -154,60 +113,29 @@ public class ExpressionFactory implements IExpressionFactory, IParserConstants {
 		return new Matches((Expression) lhs, (Expression) rhs);
 	}
 
-	public IMatchExpression matchExpression(IExpression expr) {
-		return new MatchExpression((Expression) expr);
-	}
-
-	public IExpression member(IExpression target, String name) {
-		return new Member.DynamicMember((Expression) target, name);
-	}
-
-	public IExpression memberCall(IExpression target, String name, IExpression[] args) {
+	public IExpression memberCall(IExpression target, String name, IExpression... args) {
 		if (args.length == 0)
 			return member(target, name);
 
 		Expression[] eargs = convertArray(args);
-		if (KEYWORD_SATISFIES_ANY.equals(name))
-			return new Member.CapabilityIndex_satisfiesAny((Expression) target, eargs);
-		if (KEYWORD_SATISFIES_ALL.equals(name))
-			return new Member.CapabilityIndex_satisfiesAll((Expression) target, eargs);
+		if (args.length > 0) {
+			if (KEYWORD_SATISFIES_ANY.equals(name))
+				return new CapabilityIndexFunction.SatisfiesAny((Expression) target, eargs);
+			if (KEYWORD_SATISFIES_ALL.equals(name))
+				return new CapabilityIndexFunction.SatisfiesAll((Expression) target, eargs);
+		}
 
 		StringBuffer bld = new StringBuffer();
 		bld.append("Don't know how to do a member call with "); //$NON-NLS-1$
 		bld.append(name);
 		bld.append('(');
-		Array.elementsToString(bld, eargs);
+		Expression.elementsToString(bld, null, eargs);
 		bld.append(')');
 		throw new IllegalArgumentException(bld.toString());
 	}
 
-	public IExpression not(IExpression operand) {
-		if (operand instanceof Equals) {
-			Equals eq = (Equals) operand;
-			return new Equals(eq.lhs, eq.rhs, !eq.negate);
-		}
-		if (operand instanceof Compare) {
-			Compare cmp = (Compare) operand;
-			return new Compare(cmp.lhs, cmp.rhs, !cmp.compareLess, !cmp.equalOK);
-		}
-		if (operand instanceof Not)
-			return ((Not) operand).operand;
-
-		return new Not((Expression) operand);
-	}
-
-	public IExpression or(IExpression[] operands) {
-		return new Or(convertArray(operands));
-	}
-
-	public IExpression pipe(IExpression[] operands) {
-		if (operands.length == 0)
-			return null;
-
-		Expression pipe = (Expression) operands[0];
-		for (int idx = 1; idx < operands.length; ++idx)
-			pipe = ((Expression) operands[idx]).pipeFrom(pipe);
-		return pipe;
+	public IExpression union(IExpression c1, IExpression c2) {
+		return new Union((Expression) c1, (Expression) c2);
 	}
 
 	public IExpression select(IExpression collection, IExpression lambda) {
@@ -218,11 +146,15 @@ public class ExpressionFactory implements IExpressionFactory, IParserConstants {
 		return new Traverse((Expression) collection, (LambdaExpression) lambda);
 	}
 
-	public IExpression unique(IExpression collection, IExpression cache) {
-		return new Unique((Expression) collection, (Expression) cache);
+	public IExpression variable(String name) {
+		if (name.equals(IExpressionConstants.VARIABLE_EVERYTHING))
+			return EVERYTHING;
+		if (name.equals(VARIABLE_TRANSLATIONS))
+			return TRANSLATIONS;
+		return super.variable(name);
 	}
 
-	public IExpression variable(String name) {
-		return Variable.create(name);
+	public IExpression unique(IExpression collection, IExpression cache) {
+		return new Unique((Expression) collection, (Expression) cache);
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/QLUtil.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/QLUtil.java
new file mode 100644
index 000000000..6d790b25b
--- /dev/null
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/QLUtil.java
@@ -0,0 +1,96 @@
+/*******************************************************************************
+ * Copyright (c) 2009 Cloudsmith Inc. and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Cloudsmith Inc. - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.equinox.internal.p2.ql.expression;
+
+import java.util.*;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.query.IQueryResult;
+
+/**
+ * The base class of the expression tree.
+ */
+public abstract class QLUtil implements IExpression, IQLConstants {
+
+	static Set<?> asSet(Object val, boolean forcePrivateCopy) {
+		if (val == null)
+			throw new IllegalArgumentException("Cannot convert null into an set"); //$NON-NLS-1$
+
+		if (val instanceof IRepeatableIterator<?>) {
+			Object provider = ((IRepeatableIterator<?>) val).getIteratorProvider();
+			if (!forcePrivateCopy) {
+				if (provider instanceof Set<?>)
+					return (Set<?>) provider;
+				if (provider instanceof IQueryResult<?>)
+					return ((IQueryResult<?>) provider).unmodifiableSet();
+			}
+
+			if (provider instanceof Collection<?>)
+				val = provider;
+		} else {
+			if (!forcePrivateCopy) {
+				if (val instanceof Set<?>)
+					return (Set<?>) val;
+				if (val instanceof IQueryResult<?>)
+					return ((IQueryResult<?>) val).unmodifiableSet();
+			}
+		}
+
+		HashSet<Object> result;
+		if (val instanceof Collection<?>)
+			result = new HashSet<Object>((Collection<?>) val);
+		else {
+			result = new HashSet<Object>();
+			Iterator<?> iterator = RepeatableIterator.create(val);
+			while (iterator.hasNext())
+				result.add(iterator.next());
+		}
+		return result;
+	}
+
+	/**
+	 * Checks if the expression will make repeated requests for the 'everything' iterator.
+	 * @return <code>true</code> if repeated requests will be made, <code>false</code> if not.
+	 */
+	public static boolean needsTranslationSupport(IExpression expression) {
+		final boolean[] translationSupportNeeded = new boolean[] {false};
+		((Expression) expression).accept(new IExpressionVisitor() {
+			public boolean visit(IExpression expr) {
+				if (expr.getExpressionType() == TYPE_MEMBER && VARIABLE_TRANSLATIONS.equals(ExpressionUtil.getName(expr))) {
+					translationSupportNeeded[0] = true;
+					return false;
+				}
+				return true;
+			}
+		});
+		return translationSupportNeeded[0];
+	}
+
+	/**
+	 * Checks if the expression will make repeated requests for the 'everything' iterator.
+	 * @return <code>true</code> if repeated requests will be made, <code>false</code> if not.
+	 */
+	static boolean needsRepeadedAccessToEverything(Expression expression) {
+		final boolean[] repeatedAccessNeeded = new boolean[] {false};
+		expression.accept(new IExpressionVisitor() {
+			public boolean visit(IExpression expr) {
+				// FIXME Needs proper counting
+				if (expr == QLFactory.EVERYTHING) {
+					repeatedAccessNeeded[0] = true;
+					return false;
+				}
+				return true;
+			}
+		});
+		// return repeatedAccessNeeded[0];
+		return true;
+	}
+}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/RangeFunction.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/RangeFunction.java
index df684b342..6733f73f9 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/RangeFunction.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/RangeFunction.java
@@ -10,17 +10,16 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
 import org.eclipse.equinox.p2.metadata.VersionRange;
 
 /**
  * A function that creates a {@link VersionRange} from a String
  */
-final class RangeFunction extends Function {
+public final class RangeFunction extends Function {
 
 	public RangeFunction(Expression[] operands) {
 		super(assertLength(operands, 1, 1, KEYWORD_RANGE));
-		assertNotBoolean(operands[0], "parameter"); //$NON-NLS-1$
-		assertNotCollection(operands[0], "parameter"); //$NON-NLS-1$
 	}
 
 	boolean assertSingleArgumentClass(Object v) {
@@ -31,7 +30,7 @@ final class RangeFunction extends Function {
 		return new VersionRange((String) arg);
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_RANGE;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Select.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Select.java
index f54ced61d..9ea863a0e 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Select.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Select.java
@@ -11,27 +11,25 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.Iterator;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
 import org.eclipse.equinox.internal.p2.ql.MatchIteratorFilter;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * An expression that yields a new collection consisting of all elements of the
  * <code>collection</code> for which the <code>filter</code> yields <code>true</code>.
  */
-final class Select extends CollectionFilter {
+final class Select extends CollectionFilter implements IQLExpression {
 	Select(Expression collection, LambdaExpression lambda) {
 		super(collection, lambda);
 	}
 
-	public int getExpressionType() {
-		return TYPE_SELECT;
-	}
-
-	Object evaluate(IEvaluationContext context, Iterator<?> itor) {
+	protected Object evaluate(IEvaluationContext context, Iterator<?> itor) {
 		return evaluateAsIterator(context, itor);
 	}
 
-	Iterator<?> evaluateAsIterator(final IEvaluationContext context, Iterator<?> itor) {
+	protected Iterator<?> evaluateAsIterator(final IEvaluationContext context, Iterator<?> itor) {
 		return new MatchIteratorFilter<Object>(itor) {
 			protected boolean isMatch(Object val) {
 				lambda.getItemVariable().setValue(context, val);
@@ -40,8 +38,12 @@ final class Select extends CollectionFilter {
 		};
 	}
 
-	String getOperator() {
-		return KEYWORD_SELECT;
+	public int getExpressionType() {
+		return TYPE_SELECT;
+	}
+
+	public String getOperator() {
+		return IQLConstants.KEYWORD_SELECT;
 	}
 
 	boolean isCollection() {
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/SetFunction.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/SetFunction.java
index 3b0fa5248..f83275631 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/SetFunction.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/SetFunction.java
@@ -11,9 +11,10 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.HashSet;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
 
-final class SetFunction extends Function {
+public final class SetFunction extends Function implements IQLConstants {
 
 	public SetFunction(Expression[] operands) {
 		super(operands);
@@ -26,7 +27,7 @@ final class SetFunction extends Function {
 		return result;
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_SET;
 	}
 
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Traverse.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Traverse.java
index fcb67d6b0..e8b0c0489 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Traverse.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Traverse.java
@@ -11,9 +11,9 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.*;
-import org.eclipse.equinox.internal.p2.ql.SingleVariableContext;
-import org.eclipse.equinox.internal.p2.ql.parser.IParserConstants;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * An expression that will collect items recursively based on a <code>rule</code>.
@@ -22,43 +22,39 @@ import org.eclipse.equinox.p2.ql.IEvaluationContext;
  * in the new collection. All items are collected into a set and items that are already
  * in that set will not be perused again. The set becomes the result of the traversal.
  */
-final class Traverse extends CollectionFilter {
+final class Traverse extends CollectionFilter implements IQLExpression {
 
 	Traverse(Expression collection, LambdaExpression lambda) {
 		super(collection, lambda);
 	}
 
-	public int getExpressionType() {
-		return TYPE_TRAVERSE;
-	}
-
-	Object evaluate(IEvaluationContext context, Iterator<?> itor) {
+	public Object evaluate(IEvaluationContext context, Iterator<?> itor) {
 		return evaluateAsIterator(context, itor);
 	}
 
-	Iterator<?> evaluateAsIterator(IEvaluationContext context, Iterator<?> iterator) {
+	public Iterator<?> evaluateAsIterator(IEvaluationContext context, Iterator<?> iterator) {
 		HashSet<Object> collector = new HashSet<Object>();
 		while (iterator.hasNext())
 			traverse(collector, iterator.next(), context);
 		return collector.iterator();
 	}
 
-	String getOperator() {
-		return IParserConstants.KEYWORD_TRAVERSE;
+	public int getExpressionType() {
+		return TYPE_TRAVERSE;
+	}
+
+	public String getOperator() {
+		return IQLConstants.KEYWORD_TRAVERSE;
 	}
 
 	void traverse(Set<Object> collector, Object parent, IEvaluationContext context) {
 		if (collector.add(parent)) {
 			Variable variable = lambda.getItemVariable();
-			context = new SingleVariableContext(context, variable);
+			context = EvaluationContext.create(context, variable);
 			variable.setValue(context, parent);
 			Iterator<?> subIterator = lambda.evaluateAsIterator(context);
 			while (subIterator.hasNext())
 				traverse(collector, subIterator.next(), context);
 		}
 	}
-
-	boolean isCollection() {
-		return true;
-	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Unary.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Unary.java
deleted file mode 100644
index ff4e017c6..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Unary.java
+++ /dev/null
@@ -1,48 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-import org.eclipse.equinox.p2.ql.IExpressionVisitor;
-
-/**
- * The abstract base class for all unary expressions
- */
-abstract class Unary extends Expression {
-	public final Expression operand;
-
-	Unary(Expression operand) {
-		this.operand = operand;
-	}
-
-	public boolean accept(IExpressionVisitor visitor) {
-		return super.accept(visitor) && operand.accept(visitor);
-	}
-
-	public Object evaluate(IEvaluationContext context) {
-		return operand.evaluate(context);
-	}
-
-	public void toString(StringBuffer bld) {
-		bld.append(getOperator());
-		appendOperand(bld, operand, getPriority());
-	}
-
-	public Expression getOperand() {
-		return operand;
-	}
-
-	int countReferenceToEverything() {
-		return operand.countReferenceToEverything();
-	}
-
-	abstract String getOperator();
-}
\ No newline at end of file
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/UnaryCollectionFilter.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/UnaryCollectionFilter.java
index 85d2a5527..3de55abc8 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/UnaryCollectionFilter.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/UnaryCollectionFilter.java
@@ -10,37 +10,35 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
-abstract class UnaryCollectionFilter extends Unary {
+abstract class UnaryCollectionFilter extends Unary implements IQLConstants, IQLExpression {
 
 	UnaryCollectionFilter(Expression collection) {
 		super(collection);
 	}
 
+	public int hashCode() {
+		return 5 * operand.hashCode();
+	}
+
 	public Object evaluate(IEvaluationContext context) {
 		return evaluateAsIterator(context);
 	}
 
-	public void toString(StringBuffer bld) {
+	public void toString(StringBuffer bld, Variable rootVariable) {
 		if (operand instanceof Select) {
 			Select select = (Select) operand;
-			CollectionFilter.appendProlog(bld, select.operand, getOperator());
-			appendOperand(bld, select.lambda, getPriority());
+			CollectionFilter.appendProlog(bld, rootVariable, select.operand, getOperator());
+			appendOperand(bld, rootVariable, select.lambda, getPriority());
 		} else
-			CollectionFilter.appendProlog(bld, operand, getOperator());
+			CollectionFilter.appendProlog(bld, rootVariable, operand, getOperator());
 		bld.append(')');
 	}
 
-	int getPriority() {
+	public int getPriority() {
 		return PRIORITY_COLLECTION;
 	}
-
-	boolean isCollection() {
-		return true;
-	}
-
-	boolean isElementBoolean() {
-		return operand.isElementBoolean();
-	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Union.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Union.java
new file mode 100644
index 000000000..df8049a31
--- /dev/null
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Union.java
@@ -0,0 +1,50 @@
+/*******************************************************************************
+ * Copyright (c) 2009 Cloudsmith Inc. and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Cloudsmith Inc. - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.equinox.internal.p2.ql.expression;
+
+import java.util.Iterator;
+import java.util.Set;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
+
+/**
+ */
+final class Union extends Binary implements IQLConstants, IQLExpression {
+	Union(Expression operand, Expression param) {
+		super(operand, param);
+	}
+
+	public Object evaluate(IEvaluationContext context) {
+		return evaluateAsIterator(context);
+	}
+
+	public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
+		@SuppressWarnings("unchecked")
+		Set<Object> resultSet = (Set<Object>) QLUtil.asSet(lhs.evaluate(context), true);
+		Iterator<?> itor = rhs.evaluateAsIterator(context);
+		while (itor.hasNext())
+			resultSet.add(itor.next());
+		return RepeatableIterator.create(resultSet);
+	}
+
+	public int getExpressionType() {
+		return TYPE_UNION;
+	}
+
+	public String getOperator() {
+		return KEYWORD_UNION;
+	}
+
+	public int getPriority() {
+		return PRIORITY_COLLECTION;
+	}
+}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Unique.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Unique.java
index 6d55ba1ec..5d4953cea 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Unique.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Unique.java
@@ -11,14 +11,16 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.*;
+import org.eclipse.equinox.internal.p2.metadata.expression.*;
 import org.eclipse.equinox.internal.p2.ql.MatchIteratorFilter;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.ql.IQLExpression;
 
 /**
  * An expression that ensures that the elements of its collection is only returned
  * once throughout the whole query.
  */
-final class Unique extends Binary {
+final class Unique extends Binary implements IQLConstants, IQLExpression {
 	static class UniqueIterator<T> extends MatchIteratorFilter<T> {
 		private final Set<T> uniqueSet;
 
@@ -36,12 +38,14 @@ final class Unique extends Binary {
 
 	Unique(Expression collection, Expression explicitCache) {
 		super(collection, explicitCache);
-		assertNotBoolean(collection, "collection"); //$NON-NLS-1$
-		assertNotBoolean(explicitCache, "cache"); //$NON-NLS-1$
 	}
 
-	@SuppressWarnings("unchecked")
 	public Object evaluate(IEvaluationContext context) {
+		return evaluateAsIterator(context);
+	}
+
+	@SuppressWarnings("unchecked")
+	public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
 		Object explicitCache = rhs.evaluate(context);
 		Set<Object> uniqueSet;
 		if (explicitCache == null)
@@ -59,27 +63,18 @@ final class Unique extends Binary {
 		return TYPE_UNIQUE;
 	}
 
-	public void toString(StringBuffer bld) {
-		CollectionFilter.appendProlog(bld, lhs, getOperator());
-		if (rhs != Constant.NULL_CONSTANT)
-			appendOperand(bld, rhs, PRIORITY_COMMA);
+	public void toString(StringBuffer bld, Variable rootVariable) {
+		CollectionFilter.appendProlog(bld, rootVariable, lhs, getOperator());
+		if (rhs != Literal.NULL_CONSTANT)
+			appendOperand(bld, rootVariable, rhs, IExpressionConstants.PRIORITY_COMMA);
 		bld.append(')');
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_UNIQUE;
 	}
 
-	int getPriority() {
+	public int getPriority() {
 		return PRIORITY_COLLECTION;
 	}
-
-	boolean isCollection() {
-		return true;
-	}
-
-	boolean isElementBoolean() {
-		return lhs.isElementBoolean();
-	}
-
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Variable.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Variable.java
deleted file mode 100644
index bce472fd0..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/Variable.java
+++ /dev/null
@@ -1,87 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.expression;
-
-import java.util.Iterator;
-import org.eclipse.equinox.internal.p2.ql.IRepeatableIterator;
-import org.eclipse.equinox.internal.p2.ql.RepeatableIterator;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
-import org.eclipse.equinox.p2.ql.IExpression;
-
-/**
- * An expression representing a variable stack in the current thread.
- */
-class Variable extends Expression {
-
-	static final Variable EVERYTHING = new Variable(VARIABLE_EVERYTHING);
-
-	static final Variable TRANSLATIONS = new Variable(VARIABLE_TRANSLATIONS);
-
-	static final Variable ITEM = new Variable(VARIABLE_ITEM);
-
-	private final String name;
-
-	public static Variable create(String name) {
-		if (VARIABLE_ITEM.equals(name))
-			return ITEM;
-		if (VARIABLE_EVERYTHING.equals(name))
-			return EVERYTHING;
-		if (VARIABLE_TRANSLATIONS.equals(name))
-			return TRANSLATIONS;
-		return new Variable(name);
-	}
-
-	Variable(String name) {
-		this.name = name;
-	}
-
-	public final Object evaluate(IEvaluationContext context) {
-		return context.getValue(this);
-	}
-
-	public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
-		Object value = context.getValue(this);
-		if (value instanceof IRepeatableIterator<?>)
-			return ((IRepeatableIterator<?>) value).getCopy();
-
-		Iterator<?> itor = RepeatableIterator.create(value);
-		setValue(context, itor);
-		return itor;
-	}
-
-	public String getName() {
-		return name;
-	}
-
-	public final void setValue(IEvaluationContext context, Object value) {
-		context.setValue(this, value);
-	}
-
-	public void toString(StringBuffer bld) {
-		bld.append(name);
-	}
-
-	public int getExpressionType() {
-		return TYPE_VARIABLE;
-	}
-
-	int countReferenceToEverything() {
-		return IExpression.VARIABLE_EVERYTHING.equals(name) ? 1 : 0;
-	}
-
-	int getPriority() {
-		return PRIORITY_VARIABLE;
-	}
-
-	String getOperator() {
-		return "<variable>"; //$NON-NLS-1$
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/VersionFunction.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/VersionFunction.java
index 1e88287e0..cef9a70b9 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/VersionFunction.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/VersionFunction.java
@@ -10,17 +10,16 @@
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.ql.expression;
 
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
 import org.eclipse.equinox.p2.metadata.Version;
 
 /**
  * A function that creates a {@link Version} from a string
  */
-final class VersionFunction extends Function {
+public final class VersionFunction extends Function {
 
 	public VersionFunction(Expression[] operands) {
 		super(assertLength(operands, 1, 1, KEYWORD_VERSION));
-		assertNotBoolean(operands[0], "parameter"); //$NON-NLS-1$
-		assertNotCollection(operands[0], "parameter"); //$NON-NLS-1$
 	}
 
 	boolean assertSingleArgumentClass(Object v) {
@@ -31,7 +30,7 @@ final class VersionFunction extends Function {
 		return Version.create((String) arg);
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_VERSION;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/WrappedIQuery.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/WrappedIQuery.java
index 7b1d88bb9..2436976af 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/WrappedIQuery.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/expression/WrappedIQuery.java
@@ -11,16 +11,16 @@
 package org.eclipse.equinox.internal.p2.ql.expression;
 
 import java.util.Iterator;
-import org.eclipse.equinox.p2.ql.IEvaluationContext;
+import org.eclipse.equinox.internal.p2.metadata.expression.Expression;
+import org.eclipse.equinox.internal.p2.metadata.expression.ExpressionFactory;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
 import org.eclipse.equinox.p2.query.IMatchQuery;
 import org.eclipse.equinox.p2.query.IQuery;
 
-final class WrappedIQuery extends Function {
+public final class WrappedIQuery extends Function implements IQLConstants {
 
 	public WrappedIQuery(Expression[] operands) {
 		super(assertLength(operands, 1, 2, KEYWORD_IQUERY));
-		assertNotBoolean(operands[0], "parameter"); //$NON-NLS-1$
-		assertNotCollection(operands[0], "parameter"); //$NON-NLS-1$
 	}
 
 	@SuppressWarnings("unchecked")
@@ -32,7 +32,7 @@ final class WrappedIQuery extends Function {
 			if (operands.length > 1)
 				value = operands[1].evaluate(context);
 			else
-				value = Variable.ITEM.evaluate(context);
+				value = ExpressionFactory.THIS.evaluate(context);
 			return Boolean.valueOf(((IMatchQuery<Object>) query).isMatch(value));
 		}
 
@@ -43,12 +43,12 @@ final class WrappedIQuery extends Function {
 		if (operands.length > 1)
 			iterator = operands[1].evaluateAsIterator(context);
 		else
-			iterator = Variable.EVERYTHING.evaluateAsIterator(context);
+			iterator = QLFactory.EVERYTHING.evaluateAsIterator(context);
 
 		return ((IQuery<Object>) query).perform((Iterator<Object>) iterator);
 	}
 
-	String getOperator() {
+	public String getOperator() {
 		return KEYWORD_IQUERY;
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/parser/ExpressionParser.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/parser/ExpressionParser.java
deleted file mode 100644
index bd37c6d2e..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/parser/ExpressionParser.java
+++ /dev/null
@@ -1,847 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.parser;
-
-import java.util.*;
-import org.eclipse.equinox.p2.ql.*;
-
-public class ExpressionParser extends Stack<IExpression> implements IParserConstants, IExpressionParser {
-	private static final long serialVersionUID = 882034383978853143L;
-
-	private static final int TOKEN_OR = 1;
-	private static final int TOKEN_AND = 2;
-
-	private static final int TOKEN_EQUAL = 10;
-	private static final int TOKEN_NOT_EQUAL = 11;
-	private static final int TOKEN_LESS = 12;
-	private static final int TOKEN_LESS_EQUAL = 13;
-	private static final int TOKEN_GREATER = 14;
-	private static final int TOKEN_GREATER_EQUAL = 15;
-	private static final int TOKEN_MATCHES = 16;
-
-	private static final int TOKEN_NOT = 20;
-	private static final int TOKEN_DOT = 21;
-	private static final int TOKEN_COMMA = 22;
-	private static final int TOKEN_PIPE = 23;
-	private static final int TOKEN_DOLLAR = 24;
-	private static final int TOKEN_IF = 25;
-	private static final int TOKEN_ELSE = 26;
-
-	private static final int TOKEN_LP = 30;
-	private static final int TOKEN_RP = 31;
-	private static final int TOKEN_LB = 32;
-	private static final int TOKEN_RB = 33;
-	private static final int TOKEN_LC = 34;
-	private static final int TOKEN_RC = 35;
-
-	private static final int TOKEN_IDENTIFIER = 40;
-	private static final int TOKEN_LITERAL = 41;
-	private static final int TOKEN_ANY = 42;
-
-	private static final int TOKEN_NULL = 50;
-	private static final int TOKEN_TRUE = 51;
-	private static final int TOKEN_FALSE = 52;
-
-	private static final int TOKEN_LATEST = 60;
-	private static final int TOKEN_LIMIT = 61;
-	private static final int TOKEN_FIRST = 62;
-	private static final int TOKEN_FLATTEN = 63;
-	private static final int TOKEN_UNIQUE = 64;
-	private static final int TOKEN_SELECT = 65;
-	private static final int TOKEN_COLLECT = 66;
-	private static final int TOKEN_TRAVERSE = 67;
-	private static final int TOKEN_EXISTS = 68;
-	private static final int TOKEN_ALL = 69;
-
-	private static final int TOKEN_END = 0;
-	private static final int TOKEN_ERROR = -1;
-
-	private static final Map<String, Integer> keywords;
-	static {
-		keywords = new HashMap<String, Integer>();
-		keywords.put(KEYWORD_ALL, new Integer(TOKEN_ALL));
-		keywords.put(KEYWORD_COLLECT, new Integer(TOKEN_COLLECT));
-		keywords.put(KEYWORD_EXISTS, new Integer(TOKEN_EXISTS));
-		keywords.put(KEYWORD_FALSE, new Integer(TOKEN_FALSE));
-		keywords.put(KEYWORD_FIRST, new Integer(TOKEN_FIRST));
-		keywords.put(KEYWORD_FLATTEN, new Integer(TOKEN_FLATTEN));
-		keywords.put(KEYWORD_LATEST, new Integer(TOKEN_LATEST));
-		keywords.put(KEYWORD_LIMIT, new Integer(TOKEN_LIMIT));
-		keywords.put(KEYWORD_NULL, new Integer(TOKEN_NULL));
-		keywords.put(KEYWORD_SELECT, new Integer(TOKEN_SELECT));
-		keywords.put(KEYWORD_TRAVERSE, new Integer(TOKEN_TRAVERSE));
-		keywords.put(KEYWORD_TRUE, new Integer(TOKEN_TRUE));
-		keywords.put(KEYWORD_UNIQUE, new Integer(TOKEN_UNIQUE));
-		keywords.put(OPERATOR_EACH, new Integer(TOKEN_ANY));
-	}
-
-	private final IExpressionFactory factory;
-
-	private String expression;
-	private int tokenPos;
-	private int currentToken;
-	private int lastTokenPos;
-	private Object tokenValue;
-	private String rootVariable;
-
-	public ExpressionParser(IExpressionFactory factory) {
-		this.factory = factory;
-	}
-
-	public synchronized IMatchExpression parsePredicate(String exprString) {
-		expression = exprString;
-		tokenPos = 0;
-		currentToken = 0;
-		tokenValue = null;
-		rootVariable = IExpression.VARIABLE_ITEM;
-		IExpression itemVariable = factory.variable(IExpression.VARIABLE_ITEM);
-		push(itemVariable);
-		try {
-			nextToken();
-			IExpression expr = currentToken == TOKEN_END ? factory.constant(Boolean.TRUE) : parseCondition();
-			assertToken(TOKEN_END);
-			return factory.matchExpression(expr);
-		} finally {
-			popVariable(); // pop item
-		}
-	}
-
-	public synchronized <T> IContextExpression<T> parseQuery(Class<T> elementClass, String exprString) {
-		expression = exprString;
-		tokenPos = 0;
-		currentToken = 0;
-		tokenValue = null;
-		rootVariable = IExpression.VARIABLE_EVERYTHING;
-		IExpression everythingVariable = factory.variable(IExpression.VARIABLE_EVERYTHING);
-		push(everythingVariable);
-		try {
-			nextToken();
-			IExpression expr = parseCondition();
-			assertToken(TOKEN_END);
-			return factory.contextExpression(elementClass, expr);
-		} finally {
-			popVariable(); // pop context
-		}
-	}
-
-	private IExpression parseCondition() {
-		IExpression expr = parseOr();
-		if (currentToken == TOKEN_IF) {
-			nextToken();
-			IExpression ifTrue = parseOr();
-			assertToken(TOKEN_ELSE);
-			nextToken();
-			expr = factory.condition(expr, ifTrue, parseOr());
-		}
-		return expr;
-	}
-
-	private IExpression parseOr() {
-		IExpression expr = parseAnd();
-		if (currentToken != TOKEN_OR)
-			return expr;
-
-		ArrayList<IExpression> exprs = new ArrayList<IExpression>();
-		exprs.add(expr);
-		do {
-			nextToken();
-			exprs.add(parseAnd());
-		} while (currentToken == TOKEN_OR);
-		return factory.or(exprs.toArray(new IExpression[exprs.size()]));
-	}
-
-	private IExpression parseAnd() {
-		IExpression expr = parseBinary();
-		if (currentToken != TOKEN_AND)
-			return expr;
-
-		ArrayList<IExpression> exprs = new ArrayList<IExpression>();
-		exprs.add(expr);
-		do {
-			nextToken();
-			exprs.add(parseBinary());
-		} while (currentToken == TOKEN_AND);
-		return factory.and(exprs.toArray(new IExpression[exprs.size()]));
-	}
-
-	private IExpression parseBinary() {
-		IExpression expr = parseNot();
-		switch (currentToken) {
-			case TOKEN_OR :
-			case TOKEN_AND :
-			case TOKEN_RP :
-			case TOKEN_RB :
-			case TOKEN_RC :
-			case TOKEN_COMMA :
-			case TOKEN_IF :
-			case TOKEN_ELSE :
-			case TOKEN_END :
-				break;
-			case TOKEN_EQUAL :
-			case TOKEN_NOT_EQUAL :
-			case TOKEN_GREATER :
-			case TOKEN_GREATER_EQUAL :
-			case TOKEN_LESS :
-			case TOKEN_LESS_EQUAL :
-			case TOKEN_MATCHES :
-				int realToken = currentToken;
-				nextToken();
-				IExpression rhs = parseNot();
-				switch (realToken) {
-					case TOKEN_EQUAL :
-						expr = factory.equals(expr, rhs);
-						break;
-					case TOKEN_NOT_EQUAL :
-						expr = factory.not(factory.equals(expr, rhs));
-						break;
-					case TOKEN_GREATER :
-						expr = factory.greater(expr, rhs);
-						break;
-					case TOKEN_GREATER_EQUAL :
-						expr = factory.not(factory.less(expr, rhs));
-						break;
-					case TOKEN_LESS :
-						expr = factory.less(expr, rhs);
-						break;
-					case TOKEN_LESS_EQUAL :
-						expr = factory.not(factory.greater(expr, rhs));
-						break;
-					default :
-						expr = factory.matches(expr, rhs);
-				}
-				break;
-			default :
-				throw syntaxError();
-		}
-		return expr;
-	}
-
-	private IExpression parseNot() {
-		if (currentToken == TOKEN_NOT) {
-			nextToken();
-			IExpression expr = parseNot();
-			return factory.not(expr);
-		}
-		return parseCollectionExpression();
-	}
-
-	private IExpression parseCollectionExpression() {
-		IExpression expr;
-		switch (currentToken) {
-			case TOKEN_SELECT :
-			case TOKEN_COLLECT :
-			case TOKEN_EXISTS :
-			case TOKEN_FIRST :
-			case TOKEN_FLATTEN :
-			case TOKEN_ALL :
-			case TOKEN_TRAVERSE :
-			case TOKEN_LATEST :
-			case TOKEN_LIMIT :
-			case TOKEN_UNIQUE :
-				expr = getVariableOrRootMember(rootVariable);
-				break;
-			default :
-				expr = parseMember();
-				if (currentToken != TOKEN_DOT)
-					return expr;
-				nextToken();
-		}
-
-		for (;;) {
-			int filterToken = currentToken;
-			nextToken();
-			assertToken(TOKEN_LP);
-			nextToken();
-			switch (filterToken) {
-				case TOKEN_SELECT :
-					expr = factory.select(expr, parseLambdaDefinition());
-					break;
-				case TOKEN_COLLECT :
-					expr = factory.collect(expr, parseLambdaDefinition());
-					break;
-				case TOKEN_EXISTS :
-					expr = factory.exists(expr, parseLambdaDefinition());
-					break;
-				case TOKEN_FIRST :
-					expr = factory.first(expr, parseLambdaDefinition());
-					break;
-				case TOKEN_ALL :
-					expr = factory.all(expr, parseLambdaDefinition());
-					break;
-				case TOKEN_TRAVERSE :
-					expr = factory.traverse(expr, parseLambdaDefinition());
-					break;
-				case TOKEN_LATEST :
-					if (currentToken == TOKEN_RP) {
-						expr = factory.latest(expr);
-						assertToken(TOKEN_RP);
-						nextToken();
-					} else
-						expr = factory.latest(factory.select(expr, parseLambdaDefinition()));
-					break;
-				case TOKEN_FLATTEN :
-					if (currentToken == TOKEN_RP) {
-						expr = factory.flatten(expr);
-						assertToken(TOKEN_RP);
-						nextToken();
-					} else
-						expr = factory.flatten(factory.select(expr, parseLambdaDefinition()));
-					break;
-				case TOKEN_LIMIT :
-					expr = factory.limit(expr, parseCondition());
-					assertToken(TOKEN_RP);
-					nextToken();
-					break;
-				case TOKEN_UNIQUE :
-					if (currentToken == TOKEN_RP)
-						expr = factory.unique(expr, factory.constant(null));
-					else {
-						expr = factory.unique(expr, parseMember());
-						assertToken(TOKEN_RP);
-						nextToken();
-					}
-					break;
-				default :
-					throw syntaxError();
-			}
-			if (currentToken != TOKEN_DOT)
-				break;
-			nextToken();
-		}
-		return expr;
-	}
-
-	private IExpression parseMember() {
-		IExpression expr = parseConstructor();
-		String name;
-		while (currentToken == TOKEN_DOT || currentToken == TOKEN_LB) {
-			int savePos = tokenPos;
-			int saveToken = currentToken;
-			Object saveTokenValue = tokenValue;
-			nextToken();
-			if (saveToken == TOKEN_DOT) {
-				switch (currentToken) {
-					case TOKEN_SELECT :
-					case TOKEN_COLLECT :
-					case TOKEN_EXISTS :
-					case TOKEN_FIRST :
-					case TOKEN_FLATTEN :
-					case TOKEN_ALL :
-					case TOKEN_TRAVERSE :
-					case TOKEN_LATEST :
-					case TOKEN_LIMIT :
-					case TOKEN_UNIQUE :
-						tokenPos = savePos;
-						currentToken = saveToken;
-						tokenValue = saveTokenValue;
-						return expr;
-
-					case TOKEN_IDENTIFIER :
-						name = (String) tokenValue;
-						nextToken();
-						if (currentToken == TOKEN_LP) {
-							nextToken();
-							IExpression[] callArgs = parseArray();
-							assertToken(TOKEN_RP);
-							nextToken();
-							expr = factory.memberCall(expr, name, callArgs);
-						} else
-							expr = factory.memberCall(expr, name, IExpressionFactory.NO_ARGS);
-						break;
-
-					default :
-						throw syntaxError();
-				}
-			} else {
-				IExpression atExpr = parseMember();
-				assertToken(TOKEN_RB);
-				nextToken();
-				expr = factory.at(expr, atExpr);
-			}
-		}
-		return expr;
-	}
-
-	private IExpression parseLambdaDefinition() {
-		boolean endingRC = false;
-		int anyIndex = -1;
-		IExpression[] initializers = IExpressionFactory.NO_ARGS;
-		IExpression[] variables;
-		if (currentToken == TOKEN_LC) {
-			// Lambda starts without currying.
-			endingRC = true;
-			nextToken();
-			anyIndex = 0;
-			variables = parseVariables();
-			if (variables == null)
-				// empty means no pipe at the end.
-				throw syntaxError();
-		} else {
-			anyIndex = 0;
-			variables = parseVariables();
-			if (variables == null) {
-				anyIndex = -1;
-				initializers = parseArray();
-				assertToken(TOKEN_LC);
-				nextToken();
-				endingRC = true;
-				for (int idx = 0; idx < initializers.length; ++idx) {
-					IExpression initializer = initializers[idx];
-					if (initializer.getExpressionType() == IExpression.TYPE_VARIABLE && OPERATOR_EACH.equals(initializer.toString())) {
-						if (anyIndex == -1)
-							anyIndex = idx;
-						else
-							anyIndex = -1; // Second Each. This is illegal
-						break;
-					}
-				}
-				if (anyIndex == -1)
-					throw new IllegalArgumentException("Exaclty one _ must be present among the currying expressions"); //$NON-NLS-1$
-
-				variables = parseVariables();
-				if (variables == null)
-					// empty means no pipe at the end.
-					throw syntaxError();
-			}
-
-		}
-		nextToken();
-		IExpression body = parseCondition();
-		if (endingRC) {
-			assertToken(TOKEN_RC);
-			nextToken();
-		}
-
-		assertToken(TOKEN_RP);
-		nextToken();
-		IExpression each;
-		IExpression[] assignments;
-		if (initializers.length == 0) {
-			if (variables.length != 1)
-				throw new IllegalArgumentException("Must have exactly one variable unless currying is used"); //$NON-NLS-1$
-			each = variables[0];
-			assignments = IExpressionFactory.NO_ARGS;
-		} else {
-			if (initializers.length != variables.length)
-				throw new IllegalArgumentException("Number of currying expressions and variables differ"); //$NON-NLS-1$
-
-			if (initializers.length == 1) {
-				// This is just a map from _ to some variable
-				each = variables[0];
-				assignments = IExpressionFactory.NO_ARGS;
-			} else {
-				int idx;
-				each = variables[anyIndex];
-				assignments = new IExpression[initializers.length - 1];
-				for (idx = 0; idx < anyIndex; ++idx)
-					assignments[idx] = factory.assignment(variables[idx], initializers[idx]);
-				for (++idx; idx < initializers.length; ++idx)
-					assignments[idx] = factory.assignment(variables[idx], initializers[idx]);
-			}
-		}
-		return factory.lambda(each, body, assignments);
-	}
-
-	private IExpression[] parseVariables() {
-		int savePos = tokenPos;
-		int saveToken = currentToken;
-		Object saveTokenValue = tokenValue;
-		List<Object> ids = null;
-		while (currentToken == TOKEN_IDENTIFIER) {
-			if (ids == null)
-				ids = new ArrayList<Object>();
-			ids.add(tokenValue);
-			nextToken();
-			if (currentToken == TOKEN_COMMA) {
-				nextToken();
-				continue;
-			}
-			break;
-		}
-
-		if (currentToken != TOKEN_PIPE) {
-			// This was not a variable list
-			tokenPos = savePos;
-			currentToken = saveToken;
-			tokenValue = saveTokenValue;
-			return null;
-		}
-
-		if (ids == null)
-			// Empty list but otherwise OK
-			return IExpressionFactory.NO_ARGS;
-
-		int top = ids.size();
-		IExpression[] result = new IExpression[top];
-		for (int idx = 0; idx < top; ++idx) {
-			String name = (String) ids.get(idx);
-			IExpression var = factory.variable(name);
-			push(var);
-			result[idx] = var;
-		}
-		return result;
-	}
-
-	private IExpression parseConstructor() {
-		if (currentToken == TOKEN_IDENTIFIER) {
-			int savePos = tokenPos;
-			int saveToken = currentToken;
-			Object saveTokenValue = tokenValue;
-
-			Object function = factory.getFunctionMap().get(tokenValue);
-			if (function != null) {
-				nextToken();
-				if (currentToken == TOKEN_LP) {
-					nextToken();
-					IExpression[] args = currentToken == TOKEN_RP ? IExpressionFactory.NO_ARGS : parseArray();
-					assertToken(TOKEN_RP);
-					nextToken();
-					return factory.function(function, args);
-				}
-				tokenPos = savePos;
-				currentToken = saveToken;
-				tokenValue = saveTokenValue;
-			}
-		}
-		return parseUnary();
-	}
-
-	private IExpression parseUnary() {
-		IExpression expr;
-		switch (currentToken) {
-			case TOKEN_LP :
-				nextToken();
-				expr = parseCondition();
-				assertToken(TOKEN_RP);
-				nextToken();
-				break;
-			case TOKEN_LB :
-				nextToken();
-				expr = factory.array(parseArray());
-				assertToken(TOKEN_RB);
-				nextToken();
-				break;
-			case TOKEN_LITERAL :
-				expr = factory.constant(tokenValue);
-				nextToken();
-				break;
-			case TOKEN_DOLLAR :
-				expr = parseParameter();
-				break;
-			case TOKEN_IDENTIFIER :
-				expr = getVariableOrRootMember((String) tokenValue);
-				nextToken();
-				break;
-			case TOKEN_ANY :
-				expr = factory.variable(OPERATOR_EACH);
-				nextToken();
-				break;
-			case TOKEN_NULL :
-				expr = factory.constant(null);
-				nextToken();
-				break;
-			case TOKEN_TRUE :
-				expr = factory.constant(Boolean.TRUE);
-				nextToken();
-				break;
-			case TOKEN_FALSE :
-				expr = factory.constant(Boolean.FALSE);
-				nextToken();
-				break;
-			default :
-				throw syntaxError();
-		}
-		return expr;
-	}
-
-	private IExpression parseParameter() {
-		if (currentToken == TOKEN_DOLLAR) {
-			nextToken();
-
-			IExpression param = null;
-			if (currentToken == TOKEN_LITERAL && tokenValue instanceof Integer)
-				param = factory.indexedParameter(((Integer) tokenValue).intValue());
-			else if (currentToken == TOKEN_IDENTIFIER)
-				param = factory.keyedParameter((String) tokenValue);
-
-			if (param != null) {
-				nextToken();
-				return param;
-			}
-		}
-		throw syntaxError();
-	}
-
-	private IExpression[] parseArray() {
-		IExpression expr = parseCondition();
-		if (currentToken != TOKEN_COMMA)
-			return new IExpression[] {expr};
-
-		ArrayList<IExpression> operands = new ArrayList<IExpression>();
-		operands.add(expr);
-		do {
-			nextToken();
-			if (currentToken == TOKEN_LC)
-				// We don't allow lambdas in the array
-				break;
-			operands.add(parseCondition());
-		} while (currentToken == TOKEN_COMMA);
-		return operands.toArray(new IExpression[operands.size()]);
-	}
-
-	private void assertToken(int token) {
-		if (currentToken != token)
-			throw syntaxError();
-	}
-
-	private IExpression getVariableOrRootMember(String id) {
-		int idx = size();
-		while (--idx >= 0) {
-			IExpression v = get(idx);
-			if (id.equals(v.toString()))
-				return v;
-		}
-
-		if (rootVariable.equals(id))
-			throw syntaxError("No such variable: " + id); //$NON-NLS-1$
-
-		return factory.memberCall(getVariableOrRootMember(rootVariable), id, IExpressionFactory.NO_ARGS);
-	}
-
-	private void nextToken() {
-		tokenValue = null;
-		int top = expression.length();
-		char c = 0;
-		while (tokenPos < top) {
-			c = expression.charAt(tokenPos);
-			if (!Character.isWhitespace(c))
-				break;
-			++tokenPos;
-		}
-		if (tokenPos >= top) {
-			lastTokenPos = top;
-			currentToken = TOKEN_END;
-			return;
-		}
-
-		lastTokenPos = tokenPos;
-		switch (c) {
-			case '|' :
-				if (tokenPos + 1 < top && expression.charAt(tokenPos + 1) == '|') {
-					tokenValue = OPERATOR_OR;
-					currentToken = TOKEN_OR;
-					tokenPos += 2;
-				} else {
-					currentToken = TOKEN_PIPE;
-					++tokenPos;
-				}
-				break;
-
-			case '&' :
-				if (tokenPos + 1 < top && expression.charAt(tokenPos + 1) == '&') {
-					tokenValue = OPERATOR_ARRAY;
-					currentToken = TOKEN_AND;
-					tokenPos += 2;
-				} else
-					currentToken = TOKEN_ERROR;
-				break;
-
-			case '=' :
-				if (tokenPos + 1 < top && expression.charAt(tokenPos + 1) == '=') {
-					tokenValue = OPERATOR_EQUALS;
-					currentToken = TOKEN_EQUAL;
-					tokenPos += 2;
-				} else
-					currentToken = TOKEN_ERROR;
-				break;
-
-			case '!' :
-				if (tokenPos + 1 < top && expression.charAt(tokenPos + 1) == '=') {
-					tokenValue = OPERATOR_NOT_EQUALS;
-					currentToken = TOKEN_NOT_EQUAL;
-					tokenPos += 2;
-				} else {
-					currentToken = TOKEN_NOT;
-					++tokenPos;
-				}
-				break;
-
-			case '~' :
-				if (tokenPos + 1 < top && expression.charAt(tokenPos + 1) == '=') {
-					tokenValue = IParserConstants.OPERATOR_MATCHES;
-					currentToken = TOKEN_MATCHES;
-					tokenPos += 2;
-				} else
-					currentToken = TOKEN_ERROR;
-				break;
-
-			case '>' :
-				if (tokenPos + 1 < top && expression.charAt(tokenPos + 1) == '=') {
-					tokenValue = OPERATOR_GT_EQUAL;
-					currentToken = TOKEN_GREATER_EQUAL;
-					tokenPos += 2;
-				} else {
-					currentToken = TOKEN_GREATER;
-					++tokenPos;
-				}
-				break;
-
-			case '<' :
-				if (tokenPos + 1 < top && expression.charAt(tokenPos + 1) == '=') {
-					tokenValue = OPERATOR_LT_EQUAL;
-					currentToken = TOKEN_LESS_EQUAL;
-					tokenPos += 2;
-				} else {
-					currentToken = TOKEN_LESS;
-					++tokenPos;
-				}
-				break;
-
-			case '?' :
-				currentToken = TOKEN_IF;
-				++tokenPos;
-				break;
-
-			case ':' :
-				currentToken = TOKEN_ELSE;
-				++tokenPos;
-				break;
-
-			case '.' :
-				currentToken = TOKEN_DOT;
-				++tokenPos;
-				break;
-
-			case '$' :
-				currentToken = TOKEN_DOLLAR;
-				++tokenPos;
-				break;
-
-			case '{' :
-				currentToken = TOKEN_LC;
-				++tokenPos;
-				break;
-
-			case '}' :
-				currentToken = TOKEN_RC;
-				++tokenPos;
-				break;
-
-			case '(' :
-				currentToken = TOKEN_LP;
-				++tokenPos;
-				break;
-
-			case ')' :
-				currentToken = TOKEN_RP;
-				++tokenPos;
-				break;
-
-			case '[' :
-				currentToken = TOKEN_LB;
-				++tokenPos;
-				break;
-
-			case ']' :
-				currentToken = TOKEN_RB;
-				++tokenPos;
-				break;
-
-			case ',' :
-				currentToken = TOKEN_COMMA;
-				++tokenPos;
-				break;
-
-			case '"' :
-			case '\'' : {
-				int start = ++tokenPos;
-				while (tokenPos < top && expression.charAt(tokenPos) != c)
-					++tokenPos;
-				if (tokenPos == top) {
-					tokenPos = start - 1;
-					currentToken = TOKEN_ERROR;
-				} else {
-					tokenValue = expression.substring(start, tokenPos++);
-					currentToken = TOKEN_LITERAL;
-				}
-				break;
-			}
-
-			case '/' : {
-				int start = ++tokenPos;
-				StringBuffer buf = new StringBuffer();
-				while (tokenPos < top) {
-					c = expression.charAt(tokenPos);
-					if (c == '\\' && tokenPos + 1 < top) {
-						c = expression.charAt(++tokenPos);
-						if (c != '/')
-							buf.append('\\');
-					} else if (c == '/')
-						break;
-					buf.append(c);
-					++tokenPos;
-				}
-				if (tokenPos == top) {
-					tokenPos = start - 1;
-					currentToken = TOKEN_ERROR;
-				} else {
-					tokenValue = SimplePattern.compile(expression.substring(start, tokenPos++));
-					currentToken = TOKEN_LITERAL;
-				}
-				break;
-			}
-
-			default :
-				if (Character.isDigit(c)) {
-					int start = tokenPos++;
-					while (tokenPos < top && Character.isDigit(expression.charAt(tokenPos)))
-						++tokenPos;
-					tokenValue = Integer.valueOf(expression.substring(start, tokenPos));
-					currentToken = TOKEN_LITERAL;
-					break;
-				}
-				if (Character.isJavaIdentifierStart(c)) {
-					int start = tokenPos++;
-					while (tokenPos < top && Character.isJavaIdentifierPart(expression.charAt(tokenPos)))
-						++tokenPos;
-					String word = expression.substring(start, tokenPos);
-					Integer token = keywords.get(word);
-					if (token == null)
-						currentToken = TOKEN_IDENTIFIER;
-					else
-						currentToken = token.intValue();
-					tokenValue = word;
-					break;
-				}
-				throw syntaxError();
-		}
-	}
-
-	private void popVariable() {
-		if (isEmpty())
-			throw syntaxError();
-		pop();
-	}
-
-	private QLParseException syntaxError() {
-		Object tv = tokenValue;
-		if (tv == null) {
-			if (lastTokenPos >= expression.length())
-				return syntaxError("Unexpeced end of expression"); //$NON-NLS-1$
-			tv = expression.substring(lastTokenPos, lastTokenPos + 1);
-		}
-		return syntaxError("Unexpected token \"" + tv + '"'); //$NON-NLS-1$
-	}
-
-	private QLParseException syntaxError(String message) {
-		return new QLParseException(expression, message, tokenPos);
-	}
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/parser/IParserConstants.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/parser/IParserConstants.java
deleted file mode 100644
index 381ad712b..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/parser/IParserConstants.java
+++ /dev/null
@@ -1,75 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.internal.p2.ql.parser;
-
-public interface IParserConstants {
-
-	String KEYWORD_ALL = "all"; //$NON-NLS-1$
-	String KEYWORD_BOOLEAN = "boolean"; //$NON-NLS-1$
-	String KEYWORD_CAPABILITY_INDEX = "capabilityIndex"; //$NON-NLS-1$
-	String KEYWORD_CLASS = "class"; //$NON-NLS-1$
-	String KEYWORD_COLLECT = "collect"; //$NON-NLS-1$
-	String KEYWORD_EXISTS = "exists"; //$NON-NLS-1$
-	String KEYWORD_FALSE = "false"; //$NON-NLS-1$
-	String KEYWORD_FILTER = "filter"; //$NON-NLS-1$
-	String KEYWORD_FIRST = "first"; //$NON-NLS-1$
-	String KEYWORD_FLATTEN = "flatten"; //$NON-NLS-1$
-	String KEYWORD_IQUERY = "iquery"; //$NON-NLS-1$
-	String KEYWORD_LATEST = "latest"; //$NON-NLS-1$
-	String KEYWORD_LIMIT = "limit"; //$NON-NLS-1$
-	String KEYWORD_LOCALIZED_KEYS = "localizedKeys"; //$NON-NLS-1$
-	String KEYWORD_LOCALIZED_MAP = "localizedMap"; //$NON-NLS-1$
-	String KEYWORD_LOCALIZED_PROPERTY = "localizedProperty"; //$NON-NLS-1$
-	String KEYWORD_NULL = "null"; //$NON-NLS-1$
-	String KEYWORD_RANGE = "range"; //$NON-NLS-1$
-	String KEYWORD_SATISFIES_ALL = "satisfiesAll"; //$NON-NLS-1$
-	String KEYWORD_SATISFIES_ANY = "satisfiesAny"; //$NON-NLS-1$
-	String KEYWORD_SELECT = "select"; //$NON-NLS-1$
-	String KEYWORD_SET = "set"; //$NON-NLS-1$
-	String KEYWORD_TRAVERSE = "traverse"; //$NON-NLS-1$
-	String KEYWORD_TRUE = "true"; //$NON-NLS-1$
-	String KEYWORD_UNIQUE = "unique"; //$NON-NLS-1$
-	String KEYWORD_VERSION = "version"; //$NON-NLS-1$
-
-	String OPERATOR_AND = "&&"; //$NON-NLS-1$
-	String OPERATOR_ARRAY = "[]"; //$NON-NLS-1$
-	String OPERATOR_ASSIGN = "="; //$NON-NLS-1$
-	String OPERATOR_AT = "[]"; //$NON-NLS-1$
-	String OPERATOR_EACH = "_"; //$NON-NLS-1$
-	String OPERATOR_ELSE = ":"; //$NON-NLS-1$
-	String OPERATOR_EQUALS = "=="; //$NON-NLS-1$
-	String OPERATOR_GT = ">"; //$NON-NLS-1$
-	String OPERATOR_GT_EQUAL = ">="; //$NON-NLS-1$
-	String OPERATOR_IF = "?"; //$NON-NLS-1$
-	String OPERATOR_LT = "<"; //$NON-NLS-1$
-	String OPERATOR_LT_EQUAL = "<="; //$NON-NLS-1$
-	String OPERATOR_MATCHES = "~="; //$NON-NLS-1$
-	String OPERATOR_MEMBER = "."; //$NON-NLS-1$
-	String OPERATOR_NOT = "!"; //$NON-NLS-1$
-	String OPERATOR_NOT_EQUALS = "!="; //$NON-NLS-1$
-	String OPERATOR_OR = "||"; //$NON-NLS-1$
-	String OPERATOR_PARAMETER = "$"; //$NON-NLS-1$
-
-	int PRIORITY_PARAMETER = 1;
-	int PRIORITY_VARIABLE = 1;
-	int PRIORITY_LITERAL = 1;
-	int PRIORITY_CONSTRUCTOR = 2;
-	int PRIORITY_MEMBER = 3;
-	int PRIORITY_COLLECTION = 4;
-	int PRIORITY_NOT = 5;
-	int PRIORITY_BINARY = 6;
-	int PRIORITY_AND = 7;
-	int PRIORITY_OR = 8;
-	int PRIORITY_CONDITION = 9;
-	int PRIORITY_ASSIGNMENT = 10;
-	int PRIORITY_LAMBDA = 11;
-	int PRIORITY_COMMA = 12;
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/parser/QLParser.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/parser/QLParser.java
new file mode 100644
index 000000000..9a281dfd8
--- /dev/null
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/internal/p2/ql/parser/QLParser.java
@@ -0,0 +1,384 @@
+/*******************************************************************************
+ * Copyright (c) 2009 Cloudsmith Inc. and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Cloudsmith Inc. - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.equinox.internal.p2.ql.parser;
+
+import java.util.*;
+import org.eclipse.equinox.internal.p2.metadata.expression.IExpressionConstants;
+import org.eclipse.equinox.internal.p2.metadata.expression.Variable;
+import org.eclipse.equinox.internal.p2.metadata.expression.parser.ExpressionParser;
+import org.eclipse.equinox.internal.p2.ql.expression.IQLConstants;
+import org.eclipse.equinox.p2.metadata.expression.IExpression;
+import org.eclipse.equinox.p2.metadata.expression.IExpressionFactory;
+import org.eclipse.equinox.p2.ql.IQLFactory;
+import org.eclipse.equinox.p2.ql.IQLParser;
+
+public class QLParser extends ExpressionParser implements IQLParser, IQLConstants {
+	private static final long serialVersionUID = 882034383978853143L;
+
+	private static final int TOKEN_ANY = 42;
+
+	private static final int TOKEN_LATEST = 70;
+	private static final int TOKEN_LIMIT = 71;
+	private static final int TOKEN_FIRST = 72;
+	private static final int TOKEN_FLATTEN = 73;
+	private static final int TOKEN_UNIQUE = 74;
+	private static final int TOKEN_SELECT = 75;
+	private static final int TOKEN_COLLECT = 76;
+	private static final int TOKEN_TRAVERSE = 77;
+	private static final int TOKEN_INTERSECT = 78;
+	private static final int TOKEN_UNION = 79;
+
+	private static final Map<String, Integer> qlKeywords;
+	static {
+		qlKeywords = new HashMap<String, Integer>();
+		qlKeywords.putAll(keywords);
+		qlKeywords.put(KEYWORD_COLLECT, new Integer(TOKEN_COLLECT));
+		qlKeywords.put(KEYWORD_FALSE, new Integer(TOKEN_FALSE));
+		qlKeywords.put(KEYWORD_FIRST, new Integer(TOKEN_FIRST));
+		qlKeywords.put(KEYWORD_FLATTEN, new Integer(TOKEN_FLATTEN));
+		qlKeywords.put(KEYWORD_LATEST, new Integer(TOKEN_LATEST));
+		qlKeywords.put(KEYWORD_LIMIT, new Integer(TOKEN_LIMIT));
+		qlKeywords.put(KEYWORD_NULL, new Integer(TOKEN_NULL));
+		qlKeywords.put(KEYWORD_SELECT, new Integer(TOKEN_SELECT));
+		qlKeywords.put(KEYWORD_TRAVERSE, new Integer(TOKEN_TRAVERSE));
+		qlKeywords.put(KEYWORD_TRUE, new Integer(TOKEN_TRUE));
+		qlKeywords.put(KEYWORD_UNIQUE, new Integer(TOKEN_UNIQUE));
+		qlKeywords.put(KEYWORD_INTERSECT, new Integer(TOKEN_INTERSECT));
+		qlKeywords.put(KEYWORD_UNION, new Integer(TOKEN_UNION));
+		qlKeywords.put(OPERATOR_EACH, new Integer(TOKEN_ANY));
+	}
+
+	public QLParser(IQLFactory factory) {
+		super(factory);
+	}
+
+	public synchronized IExpression parseQuery(String exprString) {
+		expression = exprString;
+		tokenPos = 0;
+		currentToken = 0;
+		tokenValue = null;
+		rootVariable = IExpressionConstants.VARIABLE_EVERYTHING;
+		IExpression everythingVariable = factory.variable(IExpressionConstants.VARIABLE_EVERYTHING);
+		push(everythingVariable);
+		try {
+			nextToken();
+			IExpression expr = parseCondition();
+			assertToken(TOKEN_END);
+			return expr;
+		} finally {
+			popVariable(); // pop context
+		}
+	}
+
+	protected Map<String, Integer> keywordToTokenMap() {
+		return qlKeywords;
+	}
+
+	protected IExpression parseCondition() {
+		IExpression expr = parseOr();
+		if (currentToken == TOKEN_IF) {
+			nextToken();
+			IExpression ifTrue = parseOr();
+			assertToken(TOKEN_ELSE);
+			nextToken();
+			expr = qlFactory().condition(expr, ifTrue, parseOr());
+		}
+		return expr;
+	}
+
+	protected IExpression parseMember() {
+		IExpression expr = parseFunction();
+		String name;
+		while (currentToken == TOKEN_DOT || currentToken == TOKEN_LB) {
+			int savePos = tokenPos;
+			int saveToken = currentToken;
+			Object saveTokenValue = tokenValue;
+			nextToken();
+			if (saveToken == TOKEN_DOT) {
+				switch (currentToken) {
+					case TOKEN_IDENTIFIER :
+						name = (String) tokenValue;
+						nextToken();
+						if (currentToken == TOKEN_LP) {
+							nextToken();
+							IExpression[] callArgs = parseArray();
+							assertToken(TOKEN_RP);
+							nextToken();
+							expr = qlFactory().memberCall(expr, name, callArgs);
+						} else
+							expr = factory.member(expr, name);
+						break;
+
+					default :
+						tokenPos = savePos;
+						currentToken = saveToken;
+						tokenValue = saveTokenValue;
+						return expr;
+				}
+			} else {
+				IExpression atExpr = parseMember();
+				assertToken(TOKEN_RB);
+				nextToken();
+				expr = factory.at(expr, atExpr);
+			}
+		}
+		return expr;
+	}
+
+	protected IExpression parseFunction() {
+		if (currentToken == TOKEN_IDENTIFIER) {
+			Object function = qlFactory().getFunctionMap().get(tokenValue);
+			if (function != null) {
+				int savePos = tokenPos;
+				int saveToken = currentToken;
+				Object saveTokenValue = tokenValue;
+
+				nextToken();
+				if (currentToken == TOKEN_LP) {
+					nextToken();
+					IExpression[] args = currentToken == TOKEN_RP ? IExpressionFactory.NO_ARGS : parseArray();
+					assertToken(TOKEN_RP);
+					nextToken();
+					return qlFactory().function(function, args);
+				}
+				tokenPos = savePos;
+				currentToken = saveToken;
+				tokenValue = saveTokenValue;
+			}
+		}
+		return parseUnary();
+	}
+
+	protected IQLFactory qlFactory() {
+		return (IQLFactory) factory;
+	}
+
+	protected IExpression parseCollectionLHS() {
+		IExpression expr;
+		switch (currentToken) {
+			case TOKEN_SELECT :
+			case TOKEN_COLLECT :
+			case TOKEN_FIRST :
+			case TOKEN_FLATTEN :
+			case TOKEN_TRAVERSE :
+			case TOKEN_LATEST :
+			case TOKEN_LIMIT :
+			case TOKEN_INTERSECT :
+			case TOKEN_UNION :
+			case TOKEN_UNIQUE :
+				expr = getVariableOrRootMember(rootVariable);
+				break;
+			default :
+				expr = super.parseCollectionLHS();
+		}
+		return expr;
+	}
+
+	protected IExpression parseCollectionRHS(IExpression expr, int funcToken) {
+		switch (funcToken) {
+			case TOKEN_SELECT :
+				expr = qlFactory().select(expr, parseLambdaDefinition());
+				break;
+			case TOKEN_COLLECT :
+				expr = qlFactory().collect(expr, parseLambdaDefinition());
+				break;
+			case TOKEN_FIRST :
+				expr = qlFactory().first(expr, parseLambdaDefinition());
+				break;
+			case TOKEN_TRAVERSE :
+				expr = qlFactory().traverse(expr, parseLambdaDefinition());
+				break;
+			case TOKEN_LATEST :
+				if (currentToken == TOKEN_RP) {
+					expr = qlFactory().latest(expr);
+					assertToken(TOKEN_RP);
+					nextToken();
+				} else
+					expr = qlFactory().latest(qlFactory().select(expr, parseLambdaDefinition()));
+				break;
+			case TOKEN_FLATTEN :
+				if (currentToken == TOKEN_RP) {
+					expr = qlFactory().flatten(expr);
+					assertToken(TOKEN_RP);
+					nextToken();
+				} else
+					expr = qlFactory().flatten(qlFactory().select(expr, parseLambdaDefinition()));
+				break;
+			case TOKEN_LIMIT :
+				expr = qlFactory().limit(expr, parseCondition());
+				assertToken(TOKEN_RP);
+				nextToken();
+				break;
+			case TOKEN_INTERSECT :
+				expr = qlFactory().intersect(expr, parseCondition());
+				assertToken(TOKEN_RP);
+				nextToken();
+				break;
+			case TOKEN_UNION :
+				expr = qlFactory().union(expr, parseCondition());
+				assertToken(TOKEN_RP);
+				nextToken();
+				break;
+			case TOKEN_UNIQUE :
+				if (currentToken == TOKEN_RP)
+					expr = qlFactory().unique(expr, factory.constant(null));
+				else {
+					expr = qlFactory().unique(expr, parseMember());
+					assertToken(TOKEN_RP);
+					nextToken();
+				}
+				break;
+			default :
+				expr = super.parseCollectionRHS(expr, funcToken);
+		}
+		return expr;
+	}
+
+	protected IExpression parseUnary() {
+		IExpression expr;
+		switch (currentToken) {
+			case TOKEN_LB :
+				nextToken();
+				expr = qlFactory().array(parseArray());
+				assertToken(TOKEN_RB);
+				nextToken();
+				break;
+			case TOKEN_ANY :
+				expr = factory.variable(IQLConstants.OPERATOR_EACH);
+				nextToken();
+				break;
+			default :
+				expr = super.parseUnary();
+		}
+		return expr;
+	}
+
+	protected IExpression parseLambdaDefinition() {
+		boolean endingRC = false;
+		int anyIndex = -1;
+		IExpression[] initializers = IExpressionFactory.NO_ARGS;
+		IExpression[] variables;
+		if (currentToken == TOKEN_LC) {
+			// Lambda starts without currying.
+			endingRC = true;
+			nextToken();
+			anyIndex = 0;
+			variables = parseVariables();
+			if (variables == null)
+				// empty means no pipe at the end.
+				throw syntaxError();
+		} else {
+			anyIndex = 0;
+			variables = parseVariables();
+			if (variables == null) {
+				anyIndex = -1;
+				initializers = parseArray();
+				assertToken(TOKEN_LC);
+				nextToken();
+				endingRC = true;
+				for (int idx = 0; idx < initializers.length; ++idx) {
+					IExpression initializer = initializers[idx];
+					if (initializer instanceof Variable && IQLConstants.OPERATOR_EACH.equals(initializer.toString())) {
+						if (anyIndex == -1)
+							anyIndex = idx;
+						else
+							anyIndex = -1; // Second Each. This is illegal
+						break;
+					}
+				}
+				if (anyIndex == -1)
+					throw new IllegalArgumentException("Exaclty one _ must be present among the currying expressions"); //$NON-NLS-1$
+
+				variables = parseVariables();
+				if (variables == null)
+					// empty means no pipe at the end.
+					throw syntaxError();
+			}
+
+		}
+		nextToken();
+		IExpression body = parseCondition();
+		if (endingRC) {
+			assertToken(TOKEN_RC);
+			nextToken();
+		}
+
+		assertToken(TOKEN_RP);
+		nextToken();
+		IExpression each;
+		IExpression[] assignments;
+		IQLFactory qlFactory = qlFactory();
+		if (initializers.length == 0) {
+			if (variables.length != 1)
+				throw new IllegalArgumentException("Must have exactly one variable unless currying is used"); //$NON-NLS-1$
+			each = variables[0];
+			assignments = IExpressionFactory.NO_ARGS;
+		} else {
+			if (initializers.length != variables.length)
+				throw new IllegalArgumentException("Number of currying expressions and variables differ"); //$NON-NLS-1$
+
+			if (initializers.length == 1) {
+				// This is just a map from _ to some variable
+				each = variables[0];
+				assignments = IExpressionFactory.NO_ARGS;
+			} else {
+				int idx;
+				each = variables[anyIndex];
+				assignments = new IExpression[initializers.length - 1];
+				for (idx = 0; idx < anyIndex; ++idx)
+					assignments[idx] = qlFactory.assignment(variables[idx], initializers[idx]);
+				for (++idx; idx < initializers.length; ++idx)
+					assignments[idx] = qlFactory.assignment(variables[idx], initializers[idx]);
+			}
+		}
+		return qlFactory.lambda(each, assignments, body);
+	}
+
+	private IExpression[] parseVariables() {
+		int savePos = tokenPos;
+		int saveToken = currentToken;
+		Object saveTokenValue = tokenValue;
+		List<Object> ids = null;
+		while (currentToken == TOKEN_IDENTIFIER) {
+			if (ids == null)
+				ids = new ArrayList<Object>();
+			ids.add(tokenValue);
+			nextToken();
+			if (currentToken == TOKEN_COMMA) {
+				nextToken();
+				continue;
+			}
+			break;
+		}
+
+		if (currentToken != TOKEN_PIPE) {
+			// This was not a variable list
+			tokenPos = savePos;
+			currentToken = saveToken;
+			tokenValue = saveTokenValue;
+			return null;
+		}
+
+		if (ids == null)
+			// Empty list but otherwise OK
+			return IExpressionFactory.NO_ARGS;
+
+		int top = ids.size();
+		IExpression[] result = new IExpression[top];
+		for (int idx = 0; idx < top; ++idx) {
+			String name = (String) ids.get(idx);
+			IExpression var = factory.variable(name);
+			push(var);
+			result[idx] = var;
+		}
+		return result;
+	}
+}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IContextExpression.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IContextExpression.java
index 0b894cc92..fa0468f0f 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IContextExpression.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IContextExpression.java
@@ -11,6 +11,8 @@
 package org.eclipse.equinox.p2.ql;
 
 import java.util.Iterator;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
+import org.eclipse.equinox.p2.metadata.expression.IExpression;
 
 /**
  * This is an expression that will need access to the global variable
@@ -18,22 +20,15 @@ import java.util.Iterator;
  */
 public interface IContextExpression<T> extends IExpression {
 	/**
-	 * Returns the element class
-	 * @return The element class
-	 */
-	Class<T> getElementClass();
-
-	/**
 	 * <p>Creates a new context to be passed to a subsequent evaluation. The context
 	 * will have the variable 'everything' set to an expression that represents
 	 * the <code>everything</code> iterator filtered for instances of <code>elementClass</code>.</p>
 	 * <p>The values of the iterator will be copied if necessary (when everything is referenced
 	 * more then once).</p>
 	 * @param everything The iterator that represents all queried material.
-	 * @param params The parameters to use for the evaluation.
 	 * @return A new evaluation context.
 	 */
-	IEvaluationContext createContext(Iterator<T> everything, Object[] params);
+	IEvaluationContext createContext(Iterator<T> everything);
 
 	/**
 	 * <p>Creates a new context to be passed to a subsequent evaluation. The context
@@ -42,9 +37,27 @@ public interface IContextExpression<T> extends IExpression {
 	 * <p>The values of the iterator will be copied if necessary (when everything is referenced
 	 * more then once).</p>
 	 * @param everything The iterator that represents all queried material.
-	 * @param params The parameters to use for the evaluation.
 	 * @param translations A translation support object to be assigned to the variable 'translations'
 	 * @return A new evaluation context.
 	 */
-	IEvaluationContext createContext(Iterator<T> everything, Object[] params, ITranslationSupport translations);
+	IEvaluationContext createContext(Iterator<T> everything, ITranslationSupport translations);
+
+	/**
+	 * Returns the element class
+	 * @return The element class
+	 */
+	Class<T> getElementClass();
+
+	/**
+	 * Returns the parameters that this context expression was created with.
+	 * @return An array of parameters, possibly empty but never <code>null</code>.
+	 */
+	Object[] getParameters();
+
+	/**
+	 * Evaluate the expression and return the expected collection result as an iterator
+	 * @param context The evaluation context
+	 * @return The result of the evaluation.
+	 */
+	Iterator<T> iterator(IEvaluationContext context);
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IEvaluationContext.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IEvaluationContext.java
deleted file mode 100644
index efde9f3f4..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IEvaluationContext.java
+++ /dev/null
@@ -1,47 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009, 2010 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.p2.ql;
-
-/**
- * The evaluation context. Contexts can be nested and new contexts are pushed for each closure
- * during an evaluation of an expression.
- * @see IMatchExpression#createContext(Object[])
- * @see IContextExpression#createContext(java.util.Iterator, Object[])
- */
-public interface IEvaluationContext {
-	/**
-	 * Retrieve the value of the given <code>variable</code> from this context
-	 * @param variable The variable who's value should be retrieved
-	 * @return The current value for the variable
-	 */
-	Object getValue(IExpression variable);
-
-	/**
-	 * Set the current value for the given <code>variable</code> to <code>value</code>
-	 * @param variable The variable who's value should be set
-	 * @param value The new value for the variable.
-	 */
-	void setValue(IExpression variable, Object value);
-
-	/**
-	 * Returns the value of the parameter at the given <code>position</code>
-	 * @param position The zero based position for the parameter
-	 * @return The parameter value
-	 */
-	Object getParameter(int position);
-
-	/**
-	 * Returns the value of the parameter at the given <code>key</code>
-	 * @param key The key for the parameter
-	 * @return The parameter value
-	 */
-	Object getParameter(String key);
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IExpression.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IExpression.java
deleted file mode 100644
index 9f959f106..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IExpression.java
+++ /dev/null
@@ -1,95 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.p2.ql;
-
-import java.util.Iterator;
-
-/**
- * A node in the expression tree
- */
-public interface IExpression {
-	int TYPE_VARIABLE = 1;
-	int TYPE_PARAMETER = 2;
-	int TYPE_LITERAL = 3;
-	int TYPE_AND = 4;
-	int TYPE_OR = 5;
-	int TYPE_FUNCTION = 6;
-	int TYPE_ARRAY = 7;
-	int TYPE_AT = 8;
-	int TYPE_MEMBER = 9;
-	int TYPE_ALL = 10;
-	int TYPE_EXISTS = 11;
-	int TYPE_SELECT = 12;
-	int TYPE_COLLECT = 13;
-	int TYPE_TRAVERSE = 14;
-	int TYPE_LATEST = 15;
-	int TYPE_FLATTEN = 16;
-	int TYPE_LIMIT = 17;
-	int TYPE_FIRST = 18;
-	int TYPE_LAMBDA = 19;
-	int TYPE_EQUALS = 20;
-	int TYPE_GREATER = 21;
-	int TYPE_LESS = 22;
-	int TYPE_GREATER_EQUAL = 23;
-	int TYPE_LESS_EQUAL = 24;
-	int TYPE_MATCHES = 25;
-	int TYPE_NOT = 26;
-	int TYPE_ASSIGNMENT = 27;
-	int TYPE_CONDITION = 28;
-	int TYPE_NOT_EQUALS = 29;
-	int TYPE_UNIQUE = 30;
-
-	String VARIABLE_TRANSLATIONS = "translations"; //$NON-NLS-1$
-	String VARIABLE_EVERYTHING = "everything"; //$NON-NLS-1$
-	String VARIABLE_ITEM = "item"; //$NON-NLS-1$
-
-	/**
-	 * Let the visitor visit this instance and all expressions that this
-	 * instance contains.
-	 * @param visitor The visiting visitor.
-	 * @return <code>true</code> if the visitor should continue visiting, <code>false</code> otherwise.
-	 */
-	boolean accept(IExpressionVisitor visitor);
-
-	/**
-	 * Evaluate this expression with given context and variables.
-	 * @param context The evaluation context
-	 * @return The result of the evaluation.
-	 */
-	Object evaluate(IEvaluationContext context);
-
-	/**
-	 * Evaluate this expression with given context and variables and return a result
-	 * in the form of an iterator.
-	 * @param context The evaluation context
-	 * @return The result of the evaluation.
-	 */
-	Iterator<?> evaluateAsIterator(IEvaluationContext context);
-
-	/**
-	 * Returns the expression type (see TYPE_xxx constants).
-	 */
-	int getExpressionType();
-
-	/**
-	 * Checks if this expression will need an instance of {@link ITranslationSupport} to execute
-	 * @return <code>true</code> if translation support is needed.
-	 */
-	boolean needsTranslations();
-
-	/**
-	 * A special toString method that can be used when efficient string concatenation is
-	 * desired. Avoids the need to create new StringBuffer instances for each concatenation
-	 * when traversing the expression tree.
-	 * @param receiver The receiver of the string representation.
-	 */
-	void toString(StringBuffer receiver);
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IExpressionVisitor.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IExpressionVisitor.java
deleted file mode 100644
index 14a7fa038..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IExpressionVisitor.java
+++ /dev/null
@@ -1,25 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.p2.ql;
-
-/**
- * A general purpose visitor that will visit each node in an expression tree.
- */
-public interface IExpressionVisitor {
-	/**
-	 * The method that will be called for each expression that is
-	 * visited.
-	 * @param expression The expression that the visitor visits.
-	 * @return <code>true</code> to continue visiting other expressions or
-	 * <code>false</code> to break out.
-	 */
-	boolean accept(IExpression expression);
-}
\ No newline at end of file
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IMatchExpression.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IMatchExpression.java
deleted file mode 100644
index cd9dff4dd..000000000
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IMatchExpression.java
+++ /dev/null
@@ -1,43 +0,0 @@
-/*******************************************************************************
- * Copyright (c) 2009 Cloudsmith Inc. and others.
- * All rights reserved. This program and the accompanying materials
- * are made available under the terms of the Eclipse Public License v1.0
- * which accompanies this distribution, and is available at
- * http://www.eclipse.org/legal/epl-v10.html
- *
- * Contributors:
- *     Cloudsmith Inc. - initial API and implementation
- *******************************************************************************/
-package org.eclipse.equinox.p2.ql;
-
-/**
- * The item expression is the top expression in item queries. It introduces the
- * variable 'item' and initializes it with the item to match.
- */
-public interface IMatchExpression extends IExpression {
-	/**
-	 * <p>Creates a new context to be passed to a subsequent evaluation. The context
-	 * will introduce 'item' as an uninitialized variable and make the parameters available.
-	 * @param params The parameters to use for the evaluation.
-	 * @return A new evaluation context.
-	 */
-	IEvaluationContext createContext(Object[] params);
-
-	/**
-	 * <p>Creates a new context to be passed to a subsequent evaluation. The context
-	 * will introduce 'item' as an uninitialized variable and make the parameters available.
-	 * @param params The parameters to use for the evaluation.
-	 * @param translations A translation support object to be assigned to the variable 'translations'
-	 * @return A new evaluation context.
-	 */
-	IEvaluationContext createContext(Object[] params, ITranslationSupport translations);
-
-	/**
-	 * This method assigns <code>candidate</code> to the 'item' variable of the
-	 * <code>context</code> and then evaluates the expression.
-	 * @param context A context previously created with {@link #createContext(Object[])}
-	 * @param candidate The object to test.
-	 * @return the result of the evaluation.
-	 */
-	boolean isMatch(IEvaluationContext context, Object candidate);
-}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IQLExpression.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IQLExpression.java
new file mode 100644
index 000000000..905bb85b5
--- /dev/null
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IQLExpression.java
@@ -0,0 +1,20 @@
+package org.eclipse.equinox.p2.ql;
+
+import org.eclipse.equinox.p2.metadata.expression.IExpression;
+
+public interface IQLExpression extends IExpression {
+	int TYPE_ARRAY = 20;
+	int TYPE_ASSIGNMENT = 21;
+	int TYPE_COLLECT = 22;
+	int TYPE_CONDITION = 23;
+	int TYPE_FIRST = 24;
+	int TYPE_FLATTEN = 25;
+	int TYPE_FUNCTION = 26;
+	int TYPE_INTERSECT = 27;
+	int TYPE_LATEST = 28;
+	int TYPE_LIMIT = 29;
+	int TYPE_SELECT = 30;
+	int TYPE_TRAVERSE = 31;
+	int TYPE_UNION = 32;
+	int TYPE_UNIQUE = 33;
+}
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IExpressionFactory.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IQLFactory.java
index 3ca1ca331..501dff83f 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IExpressionFactory.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IQLFactory.java
@@ -12,30 +12,14 @@ package org.eclipse.equinox.p2.ql;
 
 import java.util.Map;
 import org.eclipse.equinox.p2.metadata.IVersionedId;
+import org.eclipse.equinox.p2.metadata.expression.IExpression;
+import org.eclipse.equinox.p2.metadata.expression.IExpressionFactory;
 
 /**
  * This inteface provides all the factory methods needed to create the all possible
  * nodes of the expression tree.
  */
-public interface IExpressionFactory {
-	IExpression[] NO_ARGS = new IExpression[0];
-
-	/**
-	 * Create a collection filter that yields true if the <code>lambda</code> yields true for
-	 * all of the elements of the <code>collection</code>
-	 * @param collection The collection providing the elements to test
-	 * @param lambda The lambda that performs the test
-	 * @return A boolean expression
-	 */
-	IExpression all(IExpression collection, IExpression lambda);
-
-	/**
-	 * Create a logical <i>and</i> of its <code>operands</code>.
-	 * @param operands The boolean operands
-	 * @return A boolean expression
-	 */
-	IExpression and(IExpression[] operands);
-
+public interface IQLFactory extends IExpressionFactory {
 	/**
 	 * Create an array of elements.
 	 * @param elements The elements of the array
@@ -52,15 +36,6 @@ public interface IExpressionFactory {
 	IExpression assignment(IExpression variable, IExpression expression);
 
 	/**
-	 * Create an lookup of <code>key</code> in the <code>target</code>.
-	 * The key expression should evaluate to a string or an integer.
-	 * @param target The target for the lookup
-	 * @param key The key to use for the lookup
-	 * @return A lookup expression
-	 */
-	IExpression at(IExpression target, IExpression key);
-
-	/**
 	 * Create an expression that collects the result of evaluating each element in a new collection.
 	 * @param collection The collection providing the elements to evaluate
 	 * @param lambda The lambda that creates each new element
@@ -80,35 +55,13 @@ public interface IExpressionFactory {
 	IExpression condition(IExpression test, IExpression ifTrue, IExpression ifFalse);
 
 	/**
-	 * Creates an expression that evaluates to the constant <code>value</code>.
-	 * @param value The constant
-	 * @return A constant expression
-	 */
-	IExpression constant(Object value);
-
-	/**
 	 * Creates a top level expression that represents a full query.
+	 * @param elementClass The element class of the queried material
 	 * @param expr The query
+	 * @param parameters The parameters of the query
 	 * @return A top level query expression
 	 */
-	<T> IContextExpression<T> contextExpression(Class<T> elementClass, IExpression expr);
-
-	/**
-	 * Create an expression that tests if <code>lhs</code> is equal to <code>rhs</code>.
-	 * @param lhs The left hand side value.
-	 * @param rhs The right hand side value.
-	 * @return A boolean expression
-	 */
-	IExpression equals(IExpression lhs, IExpression rhs);
-
-	/**
-	 * Create a collection filter that yields true if the <code>lambda</code> yields true for
-	 * at least one of the elements of the <code>collection</code>
-	 * @param collection The collection providing the elements to test
-	 * @param lambda The lambda that performs the test
-	 * @return A boolean expression
-	 */
-	IExpression exists(IExpression collection, IExpression lambda);
+	<T> IContextExpression<T> contextExpression(Class<T> elementClass, IExpression expr, Object... parameters);
 
 	/**
 	 * Create an expression that yields the first element of the
@@ -128,13 +81,13 @@ public interface IExpressionFactory {
 	IExpression flatten(IExpression collection);
 
 	/**
-	 * Given one of the value in the {@link Map} returned by {@link #getFunctionMap()}, this method
+	 * Given one of the values in the map returned by {@link #getFunctionMap()}, this method
 	 * returns a function expression.
 	 * @param function The value obtained from the map.
 	 * @param args The arguments to evaluate and pass when evaluating the function.
 	 * @return A function expression
 	 */
-	IExpression function(Object function, IExpression[] args);
+	IExpression function(Object function, IExpression... args);
 
 	/**
 	 * Returns a map of functions supported by this factory. The map is keyed by
@@ -145,45 +98,22 @@ public interface IExpressionFactory {
 	Map<String, ? extends Object> getFunctionMap();
 
 	/**
-	 * Create an expression that tests if <code>lhs</code> is greater than <code>rhs</code>.
-	 * @param lhs The left hand side value.
-	 * @param rhs The right hand side value.
-	 * @return A boolean expression
-	 */
-	IExpression greater(IExpression lhs, IExpression rhs);
-
-	/**
-	 * Creates an indexed parameter expression
-	 * @param index The index to use
-	 * @return a parameter expression
-	 */
-	IExpression indexedParameter(int index);
-
-	/**
-	 * Creates an keyed parameter expression
-	 * @param key The key to use
-	 * @return a parameter expression
+	 * Create an <i>intersection</i> of <code>c1</code> and <code>c2</code> 
+	 * @param c1 first collection
+	 * @param c2 second collection
+	 * @return An intersect expression
 	 */
-	IExpression keyedParameter(String key);
-
-	/**
-	 * Creates a lambda expression that takes exactly one variable. Suitable for use
-	 * in most collection expressions.
-	 * @param body The body of the lambda
-	 * @param variable The element variable that the lambda uses
-	 * @return A lambda expression
-	 */
-	IExpression lambda(IExpression body, IExpression variable);
+	IExpression intersect(IExpression c1, IExpression c2);
 
 	/**
 	 * Creates a lambda expression that takes more then one variable (currying). Suitable for use
 	 * in most collection expressions.
-	 * @param body The body of the lambda
 	 * @param variable The element variable that the lambda uses
+	 * @param body The body of the lambda
 	 * @param initialAssignments Assignments to evaluate once before calling the body for each element.
 	 * @return A lambda expression with currying
 	 */
-	IExpression lambda(IExpression body, IExpression variable, IExpression[] initialAssignments);
+	IExpression lambda(IExpression variable, IExpression[] initialAssignments, IExpression body);
 
 	/**
 	 * Create an expression that yields a new collection consisting of the latest version of
@@ -195,14 +125,6 @@ public interface IExpressionFactory {
 	IExpression latest(IExpression collection);
 
 	/**
-	 * Create an expression that tests if <code>lhs</code> is less than <code>rhs</code>.
-	 * @param lhs The left hand side value.
-	 * @param rhs The right hand side value.
-	 * @return A boolean expression
-	 */
-	IExpression less(IExpression lhs, IExpression rhs);
-
-	/**
 	 * Create an expression that yields a new collection consisting of the <i>n</i> first
 	 * elements of the source collection where <i>n</i> is determined by <code>limit</code>.
 	 * @param collection The source collection
@@ -211,50 +133,13 @@ public interface IExpressionFactory {
 	IExpression limit(IExpression collection, IExpression limit);
 
 	/**
-	 * Create an expression that tests if <code>lhs</code> matches <code>rhs</code>.
-	 * @param lhs The left hand side value.
-	 * @param rhs The right hand side value.
-	 * @return A boolean expression
-	 */
-	IExpression matches(IExpression lhs, IExpression rhs);
-
-	/**
-	 * Creates a top level expression suitable for predicate matching
-	 * @param expr The boolean expression
-	 * @return A top level predicate expression
-	 */
-	IMatchExpression matchExpression(IExpression expr);
-
-	/**
-	 * Creates a member accessor expression.
-	 * @param target The target for the member access
-	 * @param name The name of the member
-	 * @return A member expression
-	 */
-	IExpression member(IExpression target, String name);
-
-	/**
 	 * Creates a member call expression.
 	 * @param target The target for the member call
 	 * @param name The name of the member
 	 * @param args The arguments to use for the call
 	 * @return A member expression
 	 */
-	IExpression memberCall(IExpression target, String name, IExpression[] args);
-
-	/**
-	 * Creates an expression that negates the result of evaluating its <code>operand</code>.
-	 * @param operand The boolean expression to negate
-	 * @return A boolean expression
-	 */
-	IExpression not(IExpression operand);
-
-	/**
-	 * Create a logical <i>or</i> of its <code>operands</code>.
-	 * @param operands The boolean operands
-	 * @return A boolean expression
-	 */
-	IExpression or(IExpression[] operands);
+	IExpression memberCall(IExpression target, String name, IExpression... args);
 
 	/**
 	 * Create an expression that yields a new collection consisting of all elements of the
@@ -283,6 +168,14 @@ public interface IExpressionFactory {
 	IExpression traverse(IExpression collection, IExpression lambda);
 
 	/**
+	 * Create a <i>union</i> of <code>c1</code> and <code>c2</code> 
+	 * @param c1 first collection
+	 * @param c2 second collection
+	 * @return A union expression
+	 */
+	IExpression union(IExpression c1, IExpression c2);
+
+	/**
 	 * Create an expression that yields a new collection where each element is unique. An
 	 * optional <code>cache</code> can be provided if the uniqueness should span a larger
 	 * scope then just the source collection.
@@ -291,11 +184,4 @@ public interface IExpressionFactory {
 	 * @return A collection expression
 	 */
 	IExpression unique(IExpression collection, IExpression cache);
-
-	/**
-	 * Creates an expression that represents a variable
-	 * @param name The name of the variable
-	 * @return A variable expression
-	 */
-	IExpression variable(String name);
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IExpressionParser.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IQLParser.java
index 5dbaf6f57..8b327a3de 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IExpressionParser.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/IQLParser.java
@@ -10,20 +10,14 @@
  *******************************************************************************/
 package org.eclipse.equinox.p2.ql;
 
+import org.eclipse.equinox.p2.metadata.expression.IExpression;
+import org.eclipse.equinox.p2.metadata.expression.IExpressionParser;
+
 /**
  * A parser that produces an expression tree based on a string representation. An
- * implementation will use the {@link IExpressionFactory} to create the actual expressions
+ * implementation will use the {@link IQLFactory} to create the actual expressions
  */
-public interface IExpressionParser {
-	/**
-	 * Create a new boolean expression. The expression will have access to the global
-	 * variable 'item' and to the context parameters.
-	 * @param exprString The string representing the boolean expression.
-	 * @return The resulting expression tree.
-	 * @throws QLParseException
-	 */
-	IMatchExpression parsePredicate(String exprString);
-
+public interface IQLParser extends IExpressionParser {
 	/**
 	 * Create an arbitrary expression. The expression will have access to the global
 	 * variable 'everything' and to the context parameters.
@@ -31,5 +25,5 @@ public interface IExpressionParser {
 	 * @return The resulting expression tree.
 	 * @throws QLParseException
 	 */
-	<T> IContextExpression<T> parseQuery(Class<T> elementClass, String exprString);
+	IExpression parseQuery(String exprString);
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QL.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QL.java
index 32633cdcd..7d34a8b9c 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QL.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QL.java
@@ -12,8 +12,8 @@ package org.eclipse.equinox.p2.ql;
 
 import java.util.Iterator;
 import org.eclipse.equinox.internal.p2.ql.QueryContext;
-import org.eclipse.equinox.internal.p2.ql.expression.ExpressionFactory;
-import org.eclipse.equinox.internal.p2.ql.parser.ExpressionParser;
+import org.eclipse.equinox.internal.p2.ql.expression.QLFactory;
+import org.eclipse.equinox.internal.p2.ql.parser.QLParser;
 import org.eclipse.equinox.p2.query.IQueryable;
 
 /**
@@ -24,16 +24,16 @@ public abstract class QL {
 	 * Returns the default expression factory.
 	 * @return the default expression factory.
 	 */
-	public static IExpressionFactory getFactory() {
-		return ExpressionFactory.INSTANCE;
+	public static IQLFactory getFactory() {
+		return QLFactory.INSTANCE;
 	}
 
 	/**
 	 * Creates a new instance of the default expression parser.
 	 * @return the new parser.
 	 */
-	public static IExpressionParser newParser() {
-		return new ExpressionParser(getFactory());
+	public static IQLParser newParser() {
+		return new QLParser(getFactory());
 	}
 
 	/**
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLContextQuery.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLContextQuery.java
index 3798627fb..83e63bbbd 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLContextQuery.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLContextQuery.java
@@ -11,6 +11,8 @@
 package org.eclipse.equinox.p2.ql;
 
 import java.util.Iterator;
+import org.eclipse.equinox.internal.p2.ql.expression.QLUtil;
+import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
 import org.eclipse.equinox.p2.query.IQueryResult;
 
 /**
@@ -21,11 +23,10 @@ public class QLContextQuery<T> extends QLQuery<T> {
 
 	/**
 	 * Creates a new query instance with indexed parameters.
-	 * @param expression The expression that represents the query.
 	 * @param parameters Parameters to use for the query.
 	 */
-	public QLContextQuery(IContextExpression<T> expression, Object... parameters) {
-		super(expression.getElementClass(), parameters);
+	public QLContextQuery(IContextExpression<T> expression) {
+		super(expression.getElementClass());
 		this.expression = expression;
 	}
 
@@ -36,7 +37,7 @@ public class QLContextQuery<T> extends QLQuery<T> {
 	 * @param parameters Parameters to use for the query.
 	 */
 	public QLContextQuery(Class<T> elementClass, String expression, Object... parameters) {
-		this(parser.parseQuery(elementClass, expression), parameters);
+		this(QL.getFactory().contextExpression(elementClass, parser.parseQuery(expression), parameters));
 	}
 
 	public IQueryResult<T> perform(Iterator<T> iterator) {
@@ -45,13 +46,12 @@ public class QLContextQuery<T> extends QLQuery<T> {
 
 	public Iterator<T> evaluate(Iterator<T> iterator) {
 		IEvaluationContext ctx;
-		if (expression.needsTranslations()) {
+		if (QLUtil.needsTranslationSupport(expression)) {
 			IQueryContext<T> queryContext = QL.newQueryContext(iterator);
-			ctx = expression.createContext(iterator, parameters, queryContext.getTranslationSupport(getLocale()));
+			ctx = expression.createContext(iterator, queryContext.getTranslationSupport(getLocale()));
 		} else
-			ctx = expression.createContext(iterator, parameters);
-		@SuppressWarnings("unchecked")
-		Iterator<T> result = (Iterator<T>) expression.evaluateAsIterator(ctx);
+			ctx = expression.createContext(iterator);
+		Iterator<T> result = expression.iterator(ctx);
 		return result;
 	}
 
@@ -64,10 +64,10 @@ public class QLContextQuery<T> extends QLQuery<T> {
 		// Check if we need translation support
 		//
 		IEvaluationContext ctx;
-		if (expression.needsTranslations())
-			ctx = expression.createContext(queryContext.iterator(), parameters, queryContext.getTranslationSupport(getLocale()));
+		if (QLUtil.needsTranslationSupport(expression))
+			ctx = expression.createContext(queryContext.iterator(), queryContext.getTranslationSupport(getLocale()));
 		else
-			ctx = expression.createContext(queryContext.iterator(), parameters);
+			ctx = expression.createContext(queryContext.iterator());
 		return expression.evaluate(ctx);
 	}
 }
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLMatchQuery.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLMatchQuery.java
index 118398a23..b06750470 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLMatchQuery.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLMatchQuery.java
@@ -12,6 +12,10 @@ package org.eclipse.equinox.p2.ql;
 
 import java.util.ArrayList;
 import java.util.Iterator;
+import org.eclipse.equinox.internal.p2.metadata.expression.EvaluationContext;
+import org.eclipse.equinox.internal.p2.ql.expression.QLFactory;
+import org.eclipse.equinox.internal.p2.ql.expression.QLUtil;
+import org.eclipse.equinox.p2.metadata.expression.*;
 import org.eclipse.equinox.p2.query.IMatchQuery;
 import org.eclipse.equinox.p2.query.IQueryResult;
 
@@ -19,7 +23,7 @@ import org.eclipse.equinox.p2.query.IQueryResult;
  * An IQuery implementation that is based on the p2 query language.
  */
 public class QLMatchQuery<T> extends QLQuery<T> implements IMatchQuery<T> {
-	private final IMatchExpression expression;
+	private final IMatchExpression<T> expression;
 	private IEvaluationContext context;
 
 	/**
@@ -28,8 +32,8 @@ public class QLMatchQuery<T> extends QLQuery<T> implements IMatchQuery<T> {
 	 * @param expression The expression that represents the query.
 	 * @param parameters Parameters to use for the query.
 	 */
-	public QLMatchQuery(Class<T> instanceClass, IMatchExpression expression, Object... parameters) {
-		super(instanceClass, parameters);
+	public QLMatchQuery(Class<T> instanceClass, IMatchExpression<T> expression) {
+		super(instanceClass);
 		this.expression = expression;
 	}
 
@@ -40,7 +44,7 @@ public class QLMatchQuery<T> extends QLQuery<T> implements IMatchQuery<T> {
 	 * @param parameters Parameters to use for the query.
 	 */
 	public QLMatchQuery(Class<T> instanceClass, String expression, Object... parameters) {
-		this(instanceClass, parser.parsePredicate(expression), parameters);
+		this(instanceClass, QL.getFactory().<T> matchExpression(parser.parse(expression), parameters));
 	}
 
 	/**
@@ -64,11 +68,13 @@ public class QLMatchQuery<T> extends QLQuery<T> implements IMatchQuery<T> {
 	}
 
 	public IQueryResult<T> perform(Iterator<T> iterator) {
-		if (expression.needsTranslations()) {
+		if (QLUtil.needsTranslationSupport(expression)) {
 			IQueryContext<T> queryContext = QL.newQueryContext(iterator);
-			context = expression.createContext(parameters, queryContext.getTranslationSupport(getLocale()));
+			IExpression translations = QLFactory.TRANSLATIONS;
+			context = EvaluationContext.create(expression.createContext(), translations);
+			context.setValue(translations, queryContext.getTranslationSupport(getLocale()));
 		} else
-			context = expression.createContext(parameters);
+			context = expression.createContext();
 
 		prePerform();
 		try {
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLQuery.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLQuery.java
index a39ecb61c..07ca483fb 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLQuery.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QLQuery.java
@@ -18,16 +18,12 @@ import org.eclipse.equinox.p2.query.IQuery;
  * An IQuery 'context query' implementation that is based on the p2 query language.
  */
 public abstract class QLQuery<T> implements IQuery<T> {
-	static final IExpressionParser parser = QL.newParser();
-	static final Object[] noParameters = new Object[0];
-
+	static final IQLParser parser = QL.newParser();
 	final Class<T> elementClass;
-	final Object[] parameters;
 	private Locale locale;
 
-	protected QLQuery(Class<T> elementClass, Object[] parameters) {
+	protected QLQuery(Class<T> elementClass) {
 		this.elementClass = elementClass;
-		this.parameters = parameters;
 	}
 
 	public Locale getLocale() {
diff --git a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QueryResult.java b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QueryResult.java
index e7ee396be..f42686912 100644
--- a/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QueryResult.java
+++ b/bundles/org.eclipse.equinox.p2.ql/src/org/eclipse/equinox/p2/ql/QueryResult.java
@@ -3,8 +3,8 @@ package org.eclipse.equinox.p2.ql;
 import java.lang.reflect.Array;
 import java.util.*;
 import org.eclipse.core.runtime.IProgressMonitor;
-import org.eclipse.equinox.internal.p2.ql.IRepeatableIterator;
-import org.eclipse.equinox.internal.p2.ql.RepeatableIterator;
+import org.eclipse.equinox.internal.p2.metadata.expression.IRepeatableIterator;
+import org.eclipse.equinox.internal.p2.metadata.expression.RepeatableIterator;
 import org.eclipse.equinox.p2.query.*;
 
 class QueryResult<T> implements IQueryResult<T> {