Add Choice pattern.

ICSharpCode.NRefactory/CSharp/Ast/PatternMatching/Choice.cs

@@ -0,0 +1,33 @@
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
+// This code is distributed under MIT X11 license (for details please see \doc\license.txt)
+
+using System;
+
+namespace ICSharpCode.NRefactory.CSharp.PatternMatching
+{
+	/// <summary>
+	/// Matches one of several alternatives.
+	/// </summary>
+	public class Choice : Pattern
+	{
+		public static readonly Role<AstNode> AlternativeRole = new Role<AstNode>("Alternative", AstNode.Null);
+		
+		public Choice(params AstNode[] alternatives)
+		{
+			foreach (AstNode node in alternatives)
+				AddChild(node, AlternativeRole);
+		}
+		
+		protected internal override bool DoMatch(AstNode other, Match match)
+		{
+			var checkPoint = match.CheckPoint();
+			foreach (AstNode alt in GetChildrenByRole(AlternativeRole)) {
+				if (alt.DoMatch(other, match))
+					return true;
+				else
+					match.RestoreCheckPoint(checkPoint);
+			}
+			return false;
+		}
+	}
+}

ICSharpCode.NRefactory/CSharp/Ast/PatternMatching/Match.cs

@@ -14,6 +14,16 @@ namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 	{
 		List<KeyValuePair<string, AstNode>> results = new List<KeyValuePair<string, AstNode>>();
 		
+		internal int CheckPoint()
+		{
+			return results.Count;
+		}
+		
+		internal void RestoreCheckPoint(int checkPoint)
+		{
+			results.RemoveRange(checkPoint, results.Count - checkPoint);
+		}
+		
 		public IEnumerable<AstNode> this[string groupName] {
 			get {
 				foreach (var pair in results) {

ICSharpCode.NRefactory/ICSharpCode.NRefactory.csproj

@@ -95,6 +95,7 @@
     <Compile Include="CSharp\Ast\Expressions\UncheckedExpression.cs" />
     <Compile Include="CSharp\Ast\GeneralScope\TypeParameterDeclaration.cs" />
     <Compile Include="CSharp\Ast\MemberType.cs" />
+    <Compile Include="CSharp\Ast\PatternMatching\Choice.cs" />
     <Compile Include="CSharp\Ast\PatternMatching\AnyNode.cs" />
     <Compile Include="CSharp\Ast\PatternMatching\Backreference.cs" />
     <Compile Include="CSharp\Ast\PatternMatching\Match.cs" />