-

diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index a18cc84..4467b91 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -357,6 +357,10 @@ module ts {
         FailedAndReported = 3
     }
 
+    export interface NodeVisitor<R, P> {
+        visitSourceFile(node: SourceFile, p: P): R;
+    }
+
     export interface Node extends TextRange {
         kind: SyntaxKind;
         flags: NodeFlags;
@@ -371,6 +375,8 @@ module ts {
         locals?: SymbolTable;               // Locals associated with node (initialized by binding)
         nextContainer?: Node;               // Next container in declaration order (initialized by binding)
         localSymbol?: Symbol;               // Local symbol declared by node (initialized by binding only for exported nodes)
+        // Support for the Visitor pattern
+        accept<R, P>(visitor: NodeVisitor<R, P>, p: P): R;
     }
 
     export interface NodeArray<T> extends Array<T>, TextRange {
diff --git a/src/services/services.ts b/src/services/services.ts
index 658f29f..0877f02 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -144,7 +144,9 @@ module ts {
         public flags: NodeFlags;
         public parent: Node;
         private _children: Node[];
-
+public accept<R, P>(visitor: NodeVisitor<R, P>, p: P): R {
+    throw new Error("Node kind " + (<any>ts).SyntaxKind[this.kind] + " does not support visitor pattern");
+}
         public getSourceFile(): SourceFile {
             return getSourceFileOfNode(this);
         }
@@ -718,6 +720,10 @@ module ts {
     }
 
     class SourceFileObject extends NodeObject implements SourceFile {
+        public accept<R,P>(visitor: NodeVisitor<R,P>, p: P): R {
+            this.statements.forEach((n) => n.accept(visitor, p));
+            return visitor.visitSourceFile(this, p);
+        }
         public _declarationBrand: any;
         public fileName: string;
         public text: string;