mono/mcs/class/System.XML/System.Xml.XPath/Expression.cs

//
// System.Xml.XPath.XPathExpression support classes
//
// Author:
//   Piers Haken ([email protected])
//
// (C) 2002 Piers Haken
//
using System;
using System.IO;
using System.Collections;
using System.Xml;
using System.Xml.XPath;
using System.Xml.Xsl;

namespace System.Xml.XPath
{
#if XPATH_DEBUG
	internal class CompiledExpression : Test.Xml.XPath.XPathExpression
#else
	internal class CompiledExpression : XPathExpression
#endif
	{
		protected XmlNamespaceManager _nsm;
		protected Expression _expr;

		public CompiledExpression (Expression expr)
		{
			_expr = expr;
		}
		private CompiledExpression (CompiledExpression other)
		{
			_nsm = other._nsm;
			_expr = other._expr;
		}
#if XPATH_DEBUG
		public override Test.Xml.XPath.XPathExpression Clone () { return new CompiledExpression (this); }
#else
		public override XPathExpression Clone () { return new CompiledExpression (this); }
#endif

		public override void SetContext (XmlNamespaceManager nsManager)
		{
			_nsm = nsManager;
		}
		public override String Expression { get { return _expr.ToString (); }}
		public override XPathResultType ReturnType { get { return _expr.ReturnType; }}
		[MonoTODO]
		public override void AddSort (Object obj, IComparer cmp)
		{
			throw new NotImplementedException ();
		}
		[MonoTODO]
		public override void AddSort(object obj, XmlSortOrder sortOrder, XmlCaseOrder caseOrder, string str, XmlDataType type)
		{
			throw new NotImplementedException ();
		}

		public object Evaluate (BaseIterator iter)
		{
			return _expr.Evaluate (iter);
		}
		public XPathNodeIterator EvaluateNodeSet (BaseIterator iter)
		{
			return _expr.EvaluateNodeSet (iter);
		}
	}


	/// <summary>
	/// Summary description for Expression.
	/// </summary>
	internal abstract class Expression
	{
		public Expression ()
		{
		}
		public abstract XPathResultType ReturnType { get; }
		public virtual XPathResultType GetReturnType (BaseIterator iter) { return ReturnType; }
		public virtual object Evaluate (BaseIterator iter) { return null; }

		public BaseIterator EvaluateNodeSet (BaseIterator iter)
		{
			if (GetReturnType (iter) == XPathResultType.NodeSet)
				return (BaseIterator) Evaluate (iter);
			throw new Exception ("expected nodeset: "+ToString ());
		}
		[MonoTODO]
		public double EvaluateNumber (BaseIterator iter)
		{
			object result;
			XPathResultType type = GetReturnType (iter);
			if (type == XPathResultType.NodeSet)
			{
				result = EvaluateString (iter);
				type = XPathResultType.String;
			}
			else
				result = Evaluate (iter);

			switch (type)
			{
				case XPathResultType.Number:
					return (double) result;
				case XPathResultType.Boolean:
					return Convert.ToDouble ((bool) result);
				case XPathResultType.String:
					return XmlConvert.ToDouble ((string) result);	// TODO: spec? convert string to number
				default:
					throw new Exception (); // TODO: handle other types
			}
		}
		[MonoTODO]
		public string EvaluateString (BaseIterator iter)
		{
			object result = Evaluate (iter);
			switch (GetReturnType (iter))
			{
				case XPathResultType.Number:
					return (string) XmlConvert.ToString ((double) result);	// TODO: spec? convert number to string
				case XPathResultType.Boolean:
					return ((bool) result) ? "true" : "false";
				case XPathResultType.String:
					return (string) result;
				case XPathResultType.NodeSet:
				{
					BaseIterator iterResult = (BaseIterator) result;
					if (iterResult == null || !iterResult.MoveNext ())
						return "";
					return iterResult.Current.Value;
				}
				default:
					throw new Exception (); // TODO: handle other types
			}
		}
		[MonoTODO]
		public bool EvaluateBoolean (BaseIterator iter)
		{
			object result = Evaluate (iter);
			switch (GetReturnType (iter))
			{
				case XPathResultType.Number:
				{
					double num = (double) result;
					return (num != 0.0 && num != -0.0 && num != Double.NaN);
				}
				case XPathResultType.Boolean:
					return (bool) result;
				case XPathResultType.String:
					return ((string) result).Length != 0;
				case XPathResultType.NodeSet:
				{
					BaseIterator iterResult = (BaseIterator) result;
					return (iterResult != null && iterResult.MoveNext ());
				}
				default:
					throw new Exception (); // TODO: handle other types
			}
		}
	}

	internal abstract class ExprBinary : Expression
	{
		protected Expression _left, _right;

		public ExprBinary (Expression left, Expression right)
		{
			_left = left;
			_right = right;
		}
		public override String ToString ()
		{
			return _left.ToString () + ' ' + Operator + ' ' + _right.ToString ();
		}
		protected abstract String Operator { get; }
	}

	internal abstract class ExprBoolean : ExprBinary
	{
		public ExprBoolean (Expression left, Expression right) : base (left, right) {}
		public override XPathResultType ReturnType { get { return XPathResultType.Boolean; }}
	}

	internal class ExprOR : ExprBoolean
	{
		public ExprOR (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "or"; }}
		public override object Evaluate (BaseIterator iter)
		{
			if (_left.EvaluateBoolean (iter))
				return true;
			return _right.EvaluateBoolean (iter);
		}
	}
	internal class ExprAND : ExprBoolean
	{
		public ExprAND (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "and"; }}
		public override object Evaluate (BaseIterator iter)
		{
			if (!_left.EvaluateBoolean (iter))
				return false;
			return _right.EvaluateBoolean (iter);
		}
	}

	internal abstract class EqualityExpr : ExprBoolean
	{
		public EqualityExpr (Expression left, Expression right) : base (left, right) {}
		[MonoTODO]
		public override object Evaluate (BaseIterator iter)
		{
			XPathResultType typeL = _left.GetReturnType (iter);
			XPathResultType typeR = _right.GetReturnType (iter);
			if (typeL == XPathResultType.NodeSet || typeR == XPathResultType.NodeSet)
			{
				Expression left, right;
				if (typeL != XPathResultType.NodeSet)
				{
					left = _right;
					right = _left;
					XPathResultType typeTmp = typeL;
					typeL = typeR;
					typeR = typeTmp;
				}
				else
				{
					left = _left;
					right = _right;
				}
				if (typeR == XPathResultType.Boolean)
				{
					bool fL = left.EvaluateBoolean (iter);
					bool fR = right.EvaluateBoolean (iter);
					return Compare (Convert.ToDouble (fL), Convert.ToDouble (fR));
				}
				else
				{
					BaseIterator iterL = left.EvaluateNodeSet (iter);
					if (typeR == XPathResultType.Number)
					{
						double dR = right.EvaluateNumber (iter);
						while (iterL.MoveNext ())
							if (Compare (XPathFunctions.ToNumber (iterL.Current.Value), dR))
								return true;
					}
					else if (typeR == XPathResultType.String)
					{
						string strR = right.EvaluateString (iter);
						while (iterL.MoveNext ())
							if (Compare (iterL.Current.Value, strR))
								return true;
					}
					else if (typeR == XPathResultType.NodeSet)
					{
						BaseIterator iterR = right.EvaluateNodeSet (iter);
						ArrayList rgNodesL = new ArrayList ();
						while (iterL.MoveNext ())
							rgNodesL.Add (XPathFunctions.ToString (iterL.Current.Value));
						while (iterR.MoveNext ())
						{
							string strR = XPathFunctions.ToString (iterR.Current.Value);
							foreach (string strL in rgNodesL)
								if (Compare (strL, strR))
									return true;
						}
					}
					return false;
				}
			}
			else if (typeL == XPathResultType.Boolean || typeR == XPathResultType.Boolean)
				return Compare (_left.EvaluateBoolean (iter), _right.EvaluateBoolean (iter));
			else if (typeL == XPathResultType.Number || typeR == XPathResultType.Number)
				return Compare (_left.EvaluateNumber (iter), _right.EvaluateNumber (iter));
			else
				return Compare (_left.EvaluateString (iter), _right.EvaluateString (iter));
		}
		[MonoTODO]
		public abstract bool Compare (object arg1, object arg2);	// TODO: should probably have type-safe methods here
	}
	
	internal class ExprEQ : EqualityExpr
	{
		public ExprEQ (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "="; }}
		public override bool Compare (object arg1, object arg2)
		{
			return arg1.Equals (arg2);
		}
	}
	internal class ExprNE : EqualityExpr
	{
		public ExprNE (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "!="; }}
		public override bool Compare (object arg1, object arg2)
		{
			return !arg1.Equals (arg2);
		}
	}

	internal abstract class RelationalExpr : ExprBoolean
	{
		public RelationalExpr (Expression left, Expression right) : base (left, right) {}
		[MonoTODO]
		public override object Evaluate (BaseIterator iter)
		{
			XPathResultType typeL = _left.GetReturnType (iter);
			XPathResultType typeR = _right.GetReturnType (iter);
			if (typeL == XPathResultType.NodeSet || typeR == XPathResultType.NodeSet)
			{
				bool fReverse = false;
				Expression left, right;
				if (typeL != XPathResultType.NodeSet)
				{
					fReverse = true;
					left = _right;
					right = _left;
					XPathResultType typeTmp = typeL;
					typeL = typeR;
					typeR = typeTmp;
				}
				else
				{
					left = _left;
					right = _right;
				}
				if (typeR == XPathResultType.Boolean)
				{
					bool fL = left.EvaluateBoolean (iter);
					bool fR = right.EvaluateBoolean (iter);
					return Compare (Convert.ToDouble (fL), Convert.ToDouble (fR), fReverse);
				}
				else
				{
					BaseIterator iterL = left.EvaluateNodeSet (iter);
					if (typeR == XPathResultType.Number || typeR == XPathResultType.String)
					{
						double dR = right.EvaluateNumber (iter);
						while (iterL.MoveNext ())
							if (Compare (XPathFunctions.ToNumber (iterL.Current.Value), dR, fReverse))
								return true;
					}
					else if (typeR == XPathResultType.NodeSet)
					{
						BaseIterator iterR = right.EvaluateNodeSet (iter);
						ArrayList rgNodesL = new ArrayList ();
						while (iterL.MoveNext ())
							rgNodesL.Add (XPathFunctions.ToNumber (iterL.Current.Value));
						while (iterR.MoveNext ())
						{
							double numR = XPathFunctions.ToNumber (iterR.Current.Value);
							foreach (double numL in rgNodesL)
								if (Compare (numL, numR))
									return true;
						}
					}
					return false;
				}
			}
			else
				return Compare (_left.EvaluateNumber (iter), _right.EvaluateNumber (iter));
		}
		public abstract bool Compare (double arg1, double arg2);
		public bool Compare (double arg1, double arg2, bool fReverse)
		{
			if (fReverse)
				return Compare (arg2, arg1);
			else
				return Compare (arg1, arg2);
		}
	}
	internal class ExprGT : RelationalExpr
	{
		public ExprGT (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return ">"; }}
		public override bool Compare (double arg1, double arg2)
		{
			return arg1 > arg2;
		}
	}
	internal class ExprGE : RelationalExpr
	{
		public ExprGE (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return ">="; }}
		public override bool Compare (double arg1, double arg2)
		{
			return arg1 >= arg2;
		}
	}
	internal class ExprLT : RelationalExpr
	{
		public ExprLT (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "<"; }}
		public override bool Compare (double arg1, double arg2)
		{
			return arg1 < arg2;
		}
	}
	internal class ExprLE : RelationalExpr
	{
		public ExprLE (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "<="; }}
		public override bool Compare (double arg1, double arg2)
		{
			return arg1 <= arg2;
		}
	}


	internal abstract class ExprNumeric : ExprBinary
	{
		public ExprNumeric (Expression left, Expression right) : base (left, right) {}
		public override XPathResultType ReturnType { get { return XPathResultType.Number; }}
	}

	internal class ExprPLUS : ExprNumeric
	{
		public ExprPLUS (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "+"; }}
		public override object Evaluate (BaseIterator iter)
		{
			return _left.EvaluateNumber (iter) + _right.EvaluateNumber (iter);
		}
	}
	internal class ExprMINUS : ExprNumeric
	{
		public ExprMINUS (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "-"; }}
		public override object Evaluate (BaseIterator iter)
		{
			return _left.EvaluateNumber (iter) - _right.EvaluateNumber (iter);
		}
	}
	internal class ExprMULT : ExprNumeric
	{
		public ExprMULT (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "*"; }}
		public override object Evaluate (BaseIterator iter)
		{
			return _left.EvaluateNumber (iter) * _right.EvaluateNumber (iter);
		}
	}
	internal class ExprDIV : ExprNumeric
	{
		public ExprDIV (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "/"; }}
		public override object Evaluate (BaseIterator iter)
		{
			return _left.EvaluateNumber (iter) / _right.EvaluateNumber (iter);
		}
	}
	internal class ExprMOD : ExprNumeric
	{
		public ExprMOD (Expression left, Expression right) : base (left, right) {}
		protected override String Operator { get { return "%"; }}
		[MonoTODO]
		public override object Evaluate (BaseIterator iter)
		{
			return _left.EvaluateNumber (iter) % _right.EvaluateNumber (iter);	// TODO: spec?
		}
	}
	internal class ExprNEG : Expression
	{
		Expression _expr;
		public ExprNEG (Expression expr)
		{
			_expr = expr;
		}
		public override String ToString () { return "- " + _expr.ToString (); }
		public override XPathResultType ReturnType { get { return XPathResultType.Number; }}
		public override object Evaluate (BaseIterator iter)
		{
			return - _expr.EvaluateNumber (iter);
		}
	}


	internal abstract class NodeSet : Expression
	{
		public override XPathResultType ReturnType { get { return XPathResultType.NodeSet; }}
	}
	internal class ExprUNION : NodeSet
	{
		protected Expression _left, _right;
		public ExprUNION (NodeSet left, NodeSet right)
		{
			_left = left;
			_right = right;
		}
		public override String ToString () { return _left.ToString ()+ " | " + _right.ToString (); }
		public override object Evaluate (BaseIterator iter)
		{
			BaseIterator iterLeft = _left.EvaluateNodeSet (iter);
			BaseIterator iterRight = _right.EvaluateNodeSet (iter);
			return new UnionIterator (iter, iterLeft, iterRight);
		}
	}
	internal class ExprSLASH : NodeSet
	{
		protected Expression _left, _right;
		public ExprSLASH (Expression left, NodeSet right)
		{
			_left = left;
			_right = right;
		}
		public override String ToString () { return _left.ToString ()+ "/" + _right.ToString (); }
		public override object Evaluate (BaseIterator iter)
		{
			BaseIterator iterLeft = _left.EvaluateNodeSet (iter);
			return new SlashIterator (iterLeft, _right);
		}
	}
	internal class ExprRoot : NodeSet
	{
		public override String ToString () { return ""; }
		public override object Evaluate (BaseIterator iter)
		{
			XPathNavigator navRoot = iter.Current.Clone ();
			navRoot.MoveToRoot ();
			return new SelfIterator (navRoot, iter.Context);
		}
	}

	internal enum Axes
	{
		Ancestor,
		AncestorOrSelf,
		Attribute,
		Child,
		Descendant,
		DescendantOrSelf,
		Following,
		FollowingSibling,
		Namespace,
		Parent,
		Preceding,
		PrecedingSibling,
		Self,
	}

	internal class AxisSpecifier
	{
		protected Axes _axis;
		public AxisSpecifier (Axes axis)
		{
			_axis = axis;
		}
		public XPathNodeType NodeType
		{
			get
			{
				switch (_axis)
				{
					case Axes.Namespace:
						return XPathNodeType.Namespace;
					case Axes.Attribute:
						return XPathNodeType.Attribute;
					default:
						return XPathNodeType.Element;
				}
			}
		}
		public override string ToString ()
		{
			switch (_axis)
			{
				case Axes.Ancestor:
					return "ancestor";
				case Axes.AncestorOrSelf:
					return "ancestor-or-self";
				case Axes.Attribute:
					return "attribute";
				case Axes.Child:
					return "child";
				case Axes.Descendant:
					return "descendant";
				case Axes.DescendantOrSelf:
					return "descendant-or-self";
				case Axes.Following:
					return "following";
				case Axes.FollowingSibling:
					return "following-sibling";
				case Axes.Namespace:
					return "namespace";
				case Axes.Parent:
					return "parent";
				case Axes.Preceding:
					return "preceeding";
				case Axes.PrecedingSibling:
					return "preceeding-sibling";
				case Axes.Self:
					return "self";
				default:
					throw new IndexOutOfRangeException ();
			}
		}
		public Axes Axis { get { return _axis; }}
		public virtual BaseIterator Evaluate (BaseIterator iter)
		{
			switch (_axis)
			{
				case Axes.Ancestor:
					return new AncestorIterator (iter);
				case Axes.AncestorOrSelf:
					return new AncestorOrSelfIterator (iter);
				case Axes.Attribute:
					return new AttributeIterator (iter);
				case Axes.Child:
					return new ChildIterator (iter);
				case Axes.Descendant:
					return new DescendantIterator (iter);
				case Axes.DescendantOrSelf:
					return new DescendantOrSelfIterator (iter);
				case Axes.Following:
					return new FollowingIterator (iter);
				case Axes.FollowingSibling:
					return new FollowingSiblingIterator (iter);
				case Axes.Namespace:
					return new NamespaceIterator (iter);
				case Axes.Parent:
					return new ParentIterator (iter);
				case Axes.Preceding:
					return new PrecedingIterator (iter);
				case Axes.PrecedingSibling:
					return new PrecedingSiblingIterator (iter);
				case Axes.Self:
					return new SelfIterator (iter);
				default:
					throw new IndexOutOfRangeException ();
			}
		}
	}

	internal abstract class NodeTest
	{
		protected AxisSpecifier _axis;
		public NodeTest (AxisSpecifier axis)
		{
			_axis = axis;
		}
		public NodeTest (Axes axis)
		{
			_axis = new AxisSpecifier (axis);
		}
		public abstract bool Match (XsltContext context, XPathNavigator nav);
		public AxisSpecifier Axis { get { return _axis; }}
		public virtual BaseIterator Evaluate (BaseIterator iter)
		{
			BaseIterator iterAxis = _axis.Evaluate (iter);
			return new AxisIterator (iterAxis, this);
		}
	}

	internal class NodeTypeTest : NodeTest
	{
		protected XPathNodeType _type;
		protected String _param;
		public NodeTypeTest (Axes axis) : base (axis)
		{
			_type = _axis.NodeType;
		}
		public NodeTypeTest (Axes axis, XPathNodeType type) : base (axis)
		{
			_type = type;
		}
		[MonoTODO]
		public NodeTypeTest (Axes axis, XPathNodeType type, String param) : base (axis)
		{
			_type = type;
			_param = param;
			if (param != null && type != XPathNodeType.ProcessingInstruction)
				throw new Exception ("No argument allowed for "+ToString (_type)+"() test");	// TODO: better description
		}
		public override String ToString ()
		{
			String strType = ToString (_type);
			if (_type == XPathNodeType.ProcessingInstruction && _param != null)
				strType += "('" + _param + "')";
			else
				strType += "()";

			return _axis.ToString () + "::" + strType;
		}
		private static String ToString (XPathNodeType type)
		{
			switch (type)
			{
				case XPathNodeType.Comment:
					return "comment";
				case XPathNodeType.Text:
					return "text";
				case XPathNodeType.ProcessingInstruction:
					return "processing-instruction";
				case XPathNodeType.All:
				case XPathNodeType.Attribute:
				case XPathNodeType.Element:
					return "node";
				default:
					throw new NotImplementedException ();
			}
		}
		public override bool Match (XsltContext context, XPathNavigator nav)
		{
			XPathNodeType nodeType = nav.NodeType;
			switch (_type)
			{
				case XPathNodeType.All:
					return true;

				case XPathNodeType.ProcessingInstruction:
					if (nodeType != XPathNodeType.ProcessingInstruction)
						return false;
					if (_param != null && nav.Name != _param)
						return false;
					return true;
				
				default:
					return _type == nodeType;
			}
		}
	}
	internal class NodeNameTest : NodeTest
	{
		protected QName _name;
		public NodeNameTest (Axes axis, QName name) : base (axis)
		{
			_name = name;
		}
		public override String ToString () { return _axis.ToString () + "::" + _name.ToString (); }
		[MonoTODO]
		public override bool Match (XsltContext context, XPathNavigator nav)
		{
			// must be the correct node type
			if (nav.NodeType != _axis.NodeType)
				return false;

			if (_name.Local != null && _name.Local != "")
			{
				// test the local part of the name first
				if (_name.Local != nav.LocalName)
					return false;
			}

			// get the prefix for the given name
			String strURI1 = "";
			if (_name.Prefix != null)
			{
				strURI1 = context.LookupNamespace (_name.Prefix);	// TODO: check to see if this returns null or ""
				if (strURI1 == null)
					throw new Exception ("Invalid namespace prefix: "+_name.Prefix);
			}

			string strURI = nav.NamespaceURI;
			if (strURI == null && strURI1 == "")	// TODO: remove when bug #26855 fixed
				return true;

			// test the prefixes
			return strURI1 == nav.NamespaceURI;
		}
	}

	internal class ExprStep : NodeSet
	{
		protected NodeTest _test;
		protected Expression [] _preds;
		public ExprStep (NodeTest test, ExprPredicates preds)
		{
			_test = test;
			if (preds != null)
				_preds = preds.GetPredicates ();
		}
		public ExprStep (NodeTest test)
		{
			_test = test;
		}
		public override String ToString ()
		{
			String strExpr = _test.ToString ();
			if (_preds != null)
			{
				foreach (Expression pred in _preds)
				{
					strExpr += '[' + pred.ToString () + ']';
				}
			}
			return strExpr;
		}
		public override object Evaluate (BaseIterator iter)
		{
			BaseIterator iterStep = _test.Evaluate (iter);
			if (_preds == null)
				return iterStep;

			return new PredicateIterator (iterStep, _preds);
		}
	}


	internal class ExprPredicates
	{
		protected Expression _pred;
		protected ExprPredicates _tail;
		public ExprPredicates (Expression pred, ExprPredicates tail)
		{
			_pred = pred;
			_tail = tail;
		}
		public ExprPredicates (Expression pred)
		{
			_pred = pred;
		}
		public Expression [] GetPredicates ()
		{
			ArrayList lstPreds = new ArrayList ();
			ExprPredicates curr = this;
			while (curr != null)
			{
				lstPreds.Add (curr._pred);
				curr = curr._tail;
			}
			return (Expression []) lstPreds.ToArray (typeof (Expression));
		}
	}

	internal class ExprFilter : Expression
	{
		protected Expression _expr;
		protected Expression _pred;
		public ExprFilter (Expression expr, Expression pred)
		{
			_expr = expr;
			_pred = pred;
		}
		public override String ToString () { return "(" + _expr.ToString () + ")[" + _pred.ToString () + "]"; }
		public override XPathResultType ReturnType { get { return XPathResultType.NodeSet; }}
	}

	internal class QName
	{
		protected String _prefix;
		protected String _local;
		public QName (String prefix, String local)
		{
			_prefix = prefix;
			_local = local;
		}
		public override String ToString ()
		{
			String strLocal = (_local != null) ? _local : "*";
			if (_prefix != null)
				return _prefix + ':' + strLocal;
			return strLocal;
		}
		public String Prefix { get { return _prefix; } }
		public String Local { get { return _local; } }
	}
	internal class NCName : QName
	{
		public NCName (String local) : base (null, local) {}
	}

	internal class ExprNumber : Expression
	{
		protected double _value;
		public ExprNumber (double value)
		{
			_value = value;
		}
		public override String ToString () { return _value.ToString (); }
		public override XPathResultType ReturnType { get { return XPathResultType.Number; }}
		public override object Evaluate (BaseIterator iter)
		{
			return _value;
		}
	}
	internal class ExprLiteral : Expression
	{
		protected String _value;
		public ExprLiteral (String value)
		{
			_value = value;
		}
		public override String ToString () { return "'" + _value + "'"; }
		public override XPathResultType ReturnType { get { return XPathResultType.String; }}
		public override object Evaluate (BaseIterator iter)
		{
			return _value;
		}
	}

	internal class ExprVariable : Expression
	{
		protected QName _name;
		public ExprVariable (QName name)
		{
			_name = name;
		}
		public override String ToString () { return "$" + _name.ToString (); }
		public override XPathResultType ReturnType { get { return XPathResultType.Any; }}
		public override XPathResultType GetReturnType (BaseIterator iter)
		{
			IXsltContextVariable var = iter.Context.ResolveVariable (_name.Prefix, _name.Local);
			return var.VariableType;
		}
	}

	internal class FunctionArguments
	{
		protected Expression _arg;
		protected FunctionArguments _tail;
		public FunctionArguments (Expression arg, FunctionArguments tail)
		{
			_arg = arg;
			_tail = tail;
		}
		public Expression Arg
		{
			get { return _arg; }
		}
		public FunctionArguments Tail
		{
			get { return _tail; }
		}
	}
	internal class ExprFunctionCall : Expression
	{
		protected QName _name;
		protected ArrayList _args = new ArrayList ();
		public ExprFunctionCall (String name, FunctionArguments args)
		{
			_name = new NCName (name);
			while (args != null)
			{
				_args.Add (args.Arg);
				args = args.Tail;
			}
		}
		public override String ToString ()
		{
			String strArgs = "";
			foreach (Expression arg in _args)
			{
				if (strArgs != "")
					strArgs += ", ";
				strArgs += arg.ToString ();
			}
			return _name.ToString () + '(' + strArgs + ')';
		}
		public override XPathResultType ReturnType { get { return XPathResultType.Any; }}
		public override XPathResultType GetReturnType (BaseIterator iter)
		{
			IXsltContextFunction func = iter.Context.ResolveFunction (_name.Prefix, _name.Local, GetArgTypes (iter));
			return func.ReturnType;
		}
		private XPathResultType [] GetArgTypes (BaseIterator iter)
		{
			// TODO: can we cache these? what if the types depend on the context?
			XPathResultType [] rgArgs = new XPathResultType [_args.Count];
			for (int iArg = 0; iArg < _args.Count; iArg++)
				rgArgs [iArg] = ((Expression) _args [iArg]).GetReturnType (iter);
			return rgArgs;
		}
		public override object Evaluate (BaseIterator iter)
		{
			//special-case the 'last' and 'position' functions
			if (_args.Count == 0 && _name.Prefix == null)
			{
				if (_name.Local == "last")
				{
					return (double) iter.Count;
				}
				else if (_name.Local == "position")
				{
					return (double) iter.CurrentPosition;
				}
			}

			XPathResultType [] rgTypes = GetArgTypes (iter);
			//FIXME: what if func == null after next line?
			IXsltContextFunction func = iter.Context.ResolveFunction (_name.Prefix, _name.Local, rgTypes);
			object [] rgArgs = new object [_args.Count];
			for (int iArg = 0; iArg < _args.Count; iArg ++)
				rgArgs [iArg] = ((Expression) _args [iArg]).Evaluate (iter);
			return func.Invoke (iter.Context, rgArgs, iter.Current);
		}
	}
}