diff --git a/Jakefile.js b/Jakefile.js
index 7b85aacaa89..a63df27b824 100644
--- a/Jakefile.js
+++ b/Jakefile.js
@@ -40,6 +40,8 @@ var compilerSources = [
     "utilities.ts",
     "binder.ts",
     "checker.ts",
+    "factory.ts",
+    "visitor.ts",
     "sourcemap.ts",
     "declarationEmitter.ts",
     "emitter.ts",
@@ -60,6 +62,8 @@ var servicesSources = [
     "utilities.ts",
     "binder.ts",
     "checker.ts",
+    "factory.ts",
+    "visitor.ts",
     "sourcemap.ts",
     "declarationEmitter.ts",
     "emitter.ts",
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 21536da36ff..48abb6ae3e3 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -91,6 +91,23 @@ namespace ts {
         return undefined;
     }
 
+    /**
+     * Iterates through `array` by index and performs the callback on each element of array until the callback
+     * returns a falsey value, then returns false.
+     * If no such value is found, the callback is applied to each element of array and `true` is returned.
+     */
+    export function trueForAll<T>(array: T[], callback: (element: T, index: number) => boolean): boolean {
+        if (array) {
+            for (let i = 0, len = array.length; i < len; i++) {
+                if (!callback(array[i], i)) {
+                    return false;
+                }
+            }
+        }
+
+        return true;
+    }
+
     export function contains<T>(array: T[], value: T): boolean {
         if (array) {
             for (const v of array) {
@@ -242,8 +259,14 @@ namespace ts {
             const count = array.length;
             if (count > 0) {
                 let pos = 0;
-                let result = arguments.length <= 2 ? array[pos] : initial;
-                pos++;
+                let result: T | U;
+                if (arguments.length <= 2) {
+                    result = array[pos];
+                    pos++;
+                }
+                else {
+                    result = initial;
+                }
                 while (pos < count) {
                     result = f(<U>result, array[pos]);
                     pos++;
@@ -260,8 +283,14 @@ namespace ts {
         if (array) {
             let pos = array.length - 1;
             if (pos >= 0) {
-                let result = arguments.length <= 2 ? array[pos] : initial;
-                pos--;
+                let result: T | U;
+                if (arguments.length <= 2) {
+                    result = array[pos];
+                    pos--;
+                }
+                else {
+                    result = initial;
+                }
                 while (pos >= 0) {
                     result = f(<U>result, array[pos]);
                     pos--;
diff --git a/src/compiler/factory.ts b/src/compiler/factory.ts
new file mode 100644
index 00000000000..06eb4b98b9c
--- /dev/null
+++ b/src/compiler/factory.ts
@@ -0,0 +1,56 @@
+/// <reference path="types.ts"/>
+/// <reference path="utilities.ts"/>
+/* @internal */
+namespace ts {
+    export function createNodeArray<T extends Node>(elements?: T[], location?: TextRange): NodeArray<T>;
+    export function createNodeArray<T extends Node, TArray extends NodeArray<T>>(elements: TArray, location?: TextRange): TArray;
+    export function createNodeArray<T extends Node, TArray extends NodeArray<T>>(elements?: T[], location?: TextRange): TArray {
+        const array = <TArray>(elements || []);
+        if (location) {
+            array.pos = location.pos;
+            array.end = location.end;
+        }
+        else if (array.pos === undefined || array.end === undefined) {
+            array.pos = -1;
+            array.end = -1;
+        }
+
+        return array;
+    }
+
+    export function createNodeArrayNode<T extends Node>(elements?: (T | NodeArrayNode<T>)[]): NodeArrayNode<T> {
+        const array = <NodeArrayNode<T>>createNodeArray(elements);
+        array.kind = SyntaxKind.NodeArrayNode;
+        return array;
+    }
+
+    export function createReturn(expression?: Expression): ReturnStatement {
+        const node = <ReturnStatement>createSynthesizedNode(SyntaxKind.ReturnStatement);
+        node.expression = expression;
+        return node;
+    }
+
+    export function createStatement(expression: Expression): ExpressionStatement {
+        const node = <ExpressionStatement>createSynthesizedNode(SyntaxKind.ExpressionStatement);
+        node.expression = expression;
+        return node;
+    }
+
+    export function createVariableStatement(declarationList: VariableDeclarationList): VariableStatement {
+        const node = <VariableStatement>createSynthesizedNode(SyntaxKind.VariableStatement);
+        node.declarationList = declarationList;
+        return node;
+    }
+
+    export function createVariableDeclarationList(declarations: VariableDeclaration[]): VariableDeclarationList {
+        const node = <VariableDeclarationList>createSynthesizedNode(SyntaxKind.VariableDeclarationList);
+        node.declarations = createNodeArray(declarations);
+        return node;
+    }
+
+    export function createBlock(statements: Statement[]): Block {
+        const block = <Block>createSynthesizedNode(SyntaxKind.Block);
+        block.statements = createNodeArray(statements);
+        return block;
+    }
+}
\ No newline at end of file
diff --git a/src/compiler/tsconfig.json b/src/compiler/tsconfig.json
index ca297c087cf..9d96dfbbb21 100644
--- a/src/compiler/tsconfig.json
+++ b/src/compiler/tsconfig.json
@@ -17,6 +17,8 @@
         "utilities.ts",
         "binder.ts",
         "checker.ts",
+        "factory.ts",
+        "visitor.ts",
         "emitter.ts",
         "program.ts",
         "commandLineParser.ts",
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 5545fbd162e..d2d436f545f 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -341,6 +341,7 @@ namespace ts {
 
         // Synthesized list
         SyntaxList,
+        NodeArrayNode,
         // Enum value count
         Count,
         // Markers
@@ -444,7 +445,8 @@ namespace ts {
         decorators?: NodeArray<Decorator>;              // Array of decorators (in document order)
         modifiers?: ModifiersArray;                     // Array of modifiers
         /* @internal */ id?: number;                    // Unique id (used to look up NodeLinks)
-        parent?: Node;                                  // Parent node (initialized by binding
+        parent?: Node;                                  // Parent node (initialized by binding)
+        /* @internal */ original?: Node;                // The original node if this is an updated node.
         /* @internal */ jsDocComment?: JSDocComment;    // JSDoc for the node, if it has any.  Only for .js files.
         /* @internal */ symbol?: Symbol;                // Symbol declared by node (initialized by binding)
         /* @internal */ locals?: SymbolTable;           // Locals associated with node (initialized by binding)
@@ -456,6 +458,10 @@ namespace ts {
         hasTrailingComma?: boolean;
     }
 
+    // @kind(SyntaxKind.NodeArrayNode)
+    export interface NodeArrayNode<T> extends Node, NodeArray<T | NodeArrayNode<T>> {
+    }
+
     export interface ModifiersArray extends NodeArray<Modifier> {
         flags: number;
     }
@@ -1287,13 +1293,15 @@ namespace ts {
         statements: NodeArray<Statement>;
     }
 
+    export type ModuleReference = EntityName | ExternalModuleReference;
+
     // @kind(SyntaxKind.ImportEqualsDeclaration)
     export interface ImportEqualsDeclaration extends DeclarationStatement {
         name: Identifier;
 
         // 'EntityName' for an internal module reference, 'ExternalModuleReference' for an external
         // module reference.
-        moduleReference: EntityName | ExternalModuleReference;
+        moduleReference: ModuleReference;
     }
 
     // @kind(SyntaxKind.ExternalModuleReference)
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 02b8385d0ff..9fe32c89a69 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -1194,10 +1194,10 @@ namespace ts {
         if (node.jsDocComment) {
             return node.jsDocComment;
         }
-        // Try to recognize this pattern when node is initializer of variable declaration and JSDoc comments are on containing variable statement. 
-        // /** 
+        // Try to recognize this pattern when node is initializer of variable declaration and JSDoc comments are on containing variable statement.
+        // /**
         //   * @param {number} name
-        //   * @returns {number} 
+        //   * @returns {number}
         //   */
         // var x = function(name) { return name.length; }
         if (checkParentVariableStatement) {
@@ -1379,7 +1379,7 @@ namespace ts {
         }
     }
 
-    export function isClassElement(n: Node): boolean {
+    export function isClassElement(n: Node): n is ClassElement {
         switch (n.kind) {
             case SyntaxKind.Constructor:
             case SyntaxKind.PropertyDeclaration:
@@ -1655,8 +1655,9 @@ namespace ts {
      * @param location An optional TextRange to use to supply the new position.
      * @param flags The NodeFlags to use for the cloned node.
      * @param parent The parent for the new node.
+     * @param original An optional pointer to the original node.
      */
-    export function cloneNode<T extends Node>(node: T, location?: TextRange, flags?: NodeFlags, parent?: Node): T {
+    export function cloneNode<T extends Node>(node: T, location?: TextRange, flags?: NodeFlags, parent?: Node, original?: Node): T {
         // We don't use "clone" from core.ts here, as we need to preserve the prototype chain of
         // the original node. We also need to exclude specific properties and only include own-
         // properties (to skip members already defined on the shared prototype).
@@ -1665,7 +1666,7 @@ namespace ts {
             : <T>createSynthesizedNode(node.kind);
 
         for (const key in node) {
-            if (clone.hasOwnProperty(key) || !node.hasOwnProperty(key)) {
+            if (key === "parent" || key === "flags" || clone.hasOwnProperty(key) || !node.hasOwnProperty(key)) {
                 continue;
             }
 
@@ -1680,6 +1681,10 @@ namespace ts {
             clone.parent = parent;
         }
 
+        if (original !== undefined) {
+            clone.original = original;
+        }
+
         return clone;
     }
 
@@ -1703,8 +1708,15 @@ namespace ts {
         return node.kind === SyntaxKind.QualifiedName;
     }
 
-    export function nodeIsSynthesized(node: Node): boolean {
-        return node.pos === -1;
+    export function nodeIsSynthesized(node: TextRange): boolean {
+        return positionIsSynthesized(node.pos)
+            || positionIsSynthesized(node.end);
+    }
+
+    export function positionIsSynthesized(pos: number): boolean {
+        // This is a fast way of testing the following conditions:
+        //  pos === undefined || pos === null || isNaN(pos) || pos < 0;
+        return !(pos >= 0);
     }
 
     export function createSynthesizedNode(kind: SyntaxKind, startsOnNewLine?: boolean): Node {
@@ -1720,6 +1732,19 @@ namespace ts {
         return array;
     }
 
+    export function getOriginalNode(node: Node): Node {
+        while (node.original !== undefined) {
+            node = node.original;
+        }
+
+        return node;
+    }
+
+    export function getOriginalNodeId(node: Node) {
+        node = getOriginalNode(node);
+        return node ? getNodeId(node) : 0;
+    }
+
     export function createDiagnosticCollection(): DiagnosticCollection {
         let nonFileDiagnostics: Diagnostic[] = [];
         const fileDiagnostics: Map<Diagnostic[]> = {};
@@ -2361,9 +2386,13 @@ namespace ts {
         return 0;
     }
 
-    export function isLeftHandSideExpression(expr: Expression): boolean {
-        if (expr) {
-            switch (expr.kind) {
+    export function isLiteralExpression(node: Node): node is LiteralExpression {
+        return isLiteralKind(node.kind);
+    }
+
+    export function isLeftHandSideExpression(node: Node): node is LeftHandSideExpression {
+        if (node) {
+            switch (node.kind) {
                 case SyntaxKind.PropertyAccessExpression:
                 case SyntaxKind.ElementAccessExpression:
                 case SyntaxKind.NewExpression:
@@ -2394,6 +2423,28 @@ namespace ts {
         return false;
     }
 
+    export function isEntityName(node: Node): node is EntityName {
+        const kind = node.kind;
+        return kind === SyntaxKind.QualifiedName
+            || kind === SyntaxKind.Identifier;
+    }
+
+    export function isIdentifierNode(node: Node): node is Identifier {
+        return node.kind === SyntaxKind.Identifier;
+    }
+
+    export function isComputedPropertyName(node: Node): node is ComputedPropertyName {
+        return node.kind === SyntaxKind.ComputedPropertyName;
+    }
+
+    export function isBinaryExpression(node: Node): node is BinaryExpression {
+        return node.kind === SyntaxKind.BinaryExpression;
+    }
+
+    export function isShortHandPropertyAssignment(node: Node): node is ShorthandPropertyAssignment {
+        return node.kind === SyntaxKind.ShorthandPropertyAssignment;
+    }
+
     export function isAssignmentOperator(token: SyntaxKind): boolean {
         return token >= SyntaxKind.FirstAssignment && token <= SyntaxKind.LastAssignment;
     }
@@ -2404,6 +2455,245 @@ namespace ts {
             isClassLike(node.parent.parent);
     }
 
+    export function isExpressionNode(node: Node): node is Expression {
+        const kind = node.kind;
+        return isUnaryExpression(node)
+            || kind === SyntaxKind.ConditionalExpression
+            || kind === SyntaxKind.YieldExpression
+            || kind === SyntaxKind.ArrowFunction
+            || kind === SyntaxKind.BinaryExpression
+            || kind === SyntaxKind.SpreadElementExpression
+            || kind === SyntaxKind.AsExpression
+            || kind === SyntaxKind.OmittedExpression;
+    }
+
+    export function isDecorator(node: Node): node is Decorator {
+        return node.kind === SyntaxKind.Decorator;
+    }
+
+    export function isModifier(node: Node): node is Modifier {
+        return isModifierKind(node.kind);
+    }
+
+    /**
+     * Node test that determines whether a node is a valid type node.
+     * This differs from the existing `isTypeNode` function which
+     * determines whether a node is *part* of a TypeNode.
+     */
+    export function isTypeNodeNode(node: Node): node is TypeNode {
+        const kind = node.kind;
+        return kind === SyntaxKind.AnyKeyword
+            || kind === SyntaxKind.NumberKeyword
+            || kind === SyntaxKind.BooleanKeyword
+            || kind === SyntaxKind.StringKeyword
+            || kind === SyntaxKind.SymbolKeyword
+            || kind === SyntaxKind.VoidKeyword
+            || kind === SyntaxKind.FunctionType
+            || kind === SyntaxKind.ConstructorType
+            || kind === SyntaxKind.TypeReference
+            || kind === SyntaxKind.TypePredicate
+            || kind === SyntaxKind.TypeQuery
+            || kind === SyntaxKind.TypeLiteral
+            || kind === SyntaxKind.ArrayType
+            || kind === SyntaxKind.TupleType
+            || kind === SyntaxKind.UnionType
+            || kind === SyntaxKind.IntersectionType
+            || kind === SyntaxKind.ParenthesizedType
+            || kind === SyntaxKind.StringLiteralType
+            || kind === SyntaxKind.ExpressionWithTypeArguments
+            || kind === SyntaxKind.ThisType;
+    }
+
+    export function isStatementNode(node: Node): node is Statement {
+        return isStatement(node)
+            || isDeclarationStatement(node);
+    }
+
+    export function isDeclarationStatement(node: Node): node is DeclarationStatement {
+        const kind = node.kind;
+        return kind === SyntaxKind.FunctionDeclaration
+            || kind === SyntaxKind.MissingDeclaration
+            || kind === SyntaxKind.ClassDeclaration
+            || kind === SyntaxKind.InterfaceDeclaration
+            || kind === SyntaxKind.TypeAliasDeclaration
+            || kind === SyntaxKind.EnumDeclaration
+            || kind === SyntaxKind.ModuleDeclaration
+            || kind === SyntaxKind.ImportEqualsDeclaration
+            || kind === SyntaxKind.ExportDeclaration
+            || kind === SyntaxKind.ExportAssignment;
+    }
+
+    export function isPropertyName(node: Node): node is PropertyName {
+        const kind = node.kind;
+        return kind === SyntaxKind.Identifier
+            || kind === SyntaxKind.StringLiteral
+            || kind === SyntaxKind.NumericLiteral
+            || kind === SyntaxKind.ComputedPropertyName;
+    }
+
+    export function isConciseBody(node: Node): node is Expression | Block {
+        return isBlock(node)
+            || isExpressionNode(node);
+    }
+
+    export function isTypeParameter(node: Node): node is TypeParameterDeclaration {
+        return node.kind === SyntaxKind.TypeParameter;
+    }
+
+    export function isParameter(node: Node): node is ParameterDeclaration {
+        return node.kind === SyntaxKind.Parameter;
+    }
+
+    export function isBindingElement(node: Node): node is BindingElement {
+        return node.kind === SyntaxKind.BindingElement;
+    }
+
+    export function isObjectLiteralElement(node: Node): node is ObjectLiteralElement {
+        const kind = node.kind;
+        return kind === SyntaxKind.PropertyAssignment
+            || kind === SyntaxKind.ShorthandPropertyAssignment
+            || kind === SyntaxKind.MethodDeclaration
+            || kind === SyntaxKind.GetAccessor
+            || kind === SyntaxKind.SetAccessor
+            || kind === SyntaxKind.MissingDeclaration;
+    }
+
+    export function isTemplate(node: Node): node is LiteralExpression | TemplateExpression {
+        const kind = node.kind;
+        return kind === SyntaxKind.TemplateExpression
+            || kind === SyntaxKind.NoSubstitutionTemplateLiteral;
+    }
+
+    export function isUnaryExpression(node: Node): node is UnaryExpression {
+        const kind = node.kind;
+        return isLeftHandSideExpression(node)
+            || kind === SyntaxKind.PrefixUnaryExpression
+            || kind === SyntaxKind.PostfixUnaryExpression
+            || kind === SyntaxKind.DeleteExpression
+            || kind === SyntaxKind.TypeOfExpression
+            || kind === SyntaxKind.VoidExpression
+            || kind === SyntaxKind.AwaitExpression
+            || kind === SyntaxKind.TypeAssertionExpression;
+    }
+
+    export function isTemplateLiteralFragment(node: Node): node is TemplateLiteralFragment {
+        const kind = node.kind;
+        return kind === SyntaxKind.TemplateHead
+            || kind === SyntaxKind.TemplateMiddle
+            || kind === SyntaxKind.TemplateTail;
+    }
+
+    export function isTemplateSpan(node: Node): node is TemplateSpan {
+        return node.kind === SyntaxKind.TemplateSpan;
+    }
+
+    export function isHeritageClause(node: Node): node is HeritageClause {
+        return node.kind === SyntaxKind.HeritageClause;
+    }
+
+    export function isVariableDeclarationList(node: Node): node is VariableDeclarationList {
+        return node.kind === SyntaxKind.VariableDeclarationList;
+    }
+
+    export function isExpressionOrVariableDeclarationList(node: Node): node is Expression | VariableDeclarationList {
+        return isVariableDeclarationList(node)
+            || isExpressionNode(node);
+    }
+
+    export function isCaseBlock(node: Node): node is CaseBlock {
+        return node.kind === SyntaxKind.CaseBlock;
+    }
+
+    export function isBlock(node: Node): node is Block {
+        return node.kind === SyntaxKind.Block;
+    }
+
+    export function isCatchClause(node: Node): node is CatchClause {
+        return node.kind === SyntaxKind.CatchClause;
+    }
+
+    export function isVariableDeclaration(node: Node): node is VariableDeclaration {
+        return node.kind === SyntaxKind.VariableDeclaration;
+    }
+
+    export function isEnumMember(node: Node): node is EnumMember {
+        return node.kind === SyntaxKind.EnumMember;
+    }
+
+    export function isModuleName(node: Node): node is Identifier | LiteralExpression {
+        return node.kind === SyntaxKind.Identifier
+            || node.kind === SyntaxKind.StringLiteral;
+    }
+
+    export function isCaseOrDefaultClause(node: Node): node is CaseOrDefaultClause {
+        return node.kind === SyntaxKind.CaseClause
+            || node.kind === SyntaxKind.DefaultClause;
+    }
+
+    export function isModuleReference(node: Node): node is EntityName | ExternalModuleReference {
+        return node.kind === SyntaxKind.ExternalModuleReference
+            || isEntityName(node);
+    }
+
+    export function isImportClause(node: Node): node is ImportClause {
+        return node.kind === SyntaxKind.ImportClause;
+    }
+
+    export function isNamedImportsOrNamespaceImport(node: Node): node is NamedImports | NamespaceImport {
+        const kind = node.kind;
+        return kind === SyntaxKind.NamedImports
+            || kind === SyntaxKind.NamespaceImport;
+    }
+
+    export function isImportSpecifier(node: Node): node is ImportSpecifier {
+        return node.kind === SyntaxKind.ImportSpecifier;
+    }
+
+    export function isNamedExports(node: Node): node is NamedExports {
+        return node.kind === SyntaxKind.NamedExports;
+    }
+
+    export function isExportSpecifier(node: Node): node is ExportSpecifier {
+        return node.kind === SyntaxKind.ExportSpecifier;
+    }
+
+    export function isJsxOpeningElement(node: Node): node is JsxOpeningElement {
+        return node.kind === SyntaxKind.JsxOpeningElement;
+    }
+
+    export function isJsxClosingElement(node: Node): node is JsxClosingElement {
+        return node.kind === SyntaxKind.JsxClosingElement;
+    }
+
+    export function isJsxChild(node: Node): node is JsxChild {
+        const kind = node.kind;
+        return kind === SyntaxKind.JsxElement
+            || kind === SyntaxKind.JsxExpression
+            || kind === SyntaxKind.JsxSelfClosingElement
+            || kind === SyntaxKind.JsxText;
+    }
+
+    export function isJsxAttributeOrJsxSpreadAttribute(node: Node): node is JsxAttribute | JsxSpreadAttribute {
+        const kind = node.kind;
+        return kind === SyntaxKind.JsxAttribute
+            || kind === SyntaxKind.JsxSpreadAttribute;
+    }
+
+    export function isExpressionWithTypeArguments(node: Node): node is ExpressionWithTypeArguments {
+        return node.kind === SyntaxKind.ExpressionWithTypeArguments;
+    }
+
+    export function isModuleBody(node: Node): node is ModuleBody {
+        const kind = node.kind;
+        return kind === SyntaxKind.ModuleBlock
+            || kind === SyntaxKind.ModuleDeclaration;
+    }
+
+    export function isBindingPatternOrIdentifier(node: Node): node is (BindingPattern | Identifier) {
+        return isBindingPattern(node)
+            || isIdentifierNode(node);
+    }
+
     // Returns false if this heritage clause element's expression contains something unsupported
     // (i.e. not a name or dotted name).
     export function isSupportedExpressionWithTypeArguments(node: ExpressionWithTypeArguments): boolean {
@@ -2438,6 +2728,14 @@ namespace ts {
         return false;
     }
 
+    export function isModifiersArray(nodes: NodeArray<Node>): nodes is ModifiersArray {
+        return !isNodeArrayNode(nodes) && typeof (<ModifiersArray>nodes).flags === "number";
+    }
+
+    export function isNodeArrayNode<T extends Node>(value: Node | NodeArray<T | NodeArrayNode<T>>): value is NodeArrayNode<T> {
+        return (<Node>value).kind === SyntaxKind.NodeArrayNode;
+    }
+
     export function getLocalSymbolForExportDefault(symbol: Symbol) {
         return symbol && symbol.valueDeclaration && (symbol.valueDeclaration.flags & NodeFlags.Default) ? symbol.valueDeclaration.localSymbol : undefined;
     }
diff --git a/src/compiler/visitor.ts b/src/compiler/visitor.ts
new file mode 100644
index 00000000000..15120148d1a
--- /dev/null
+++ b/src/compiler/visitor.ts
@@ -0,0 +1,778 @@
+/// <reference path="checker.ts" />
+/// <reference path="factory.ts" />
+/* @internal */
+namespace ts {
+    /** Additional context provided to `visitEachChild` */
+    export interface LexicalEnvironment {
+        /** Starts a new lexical environment. */
+        startLexicalEnvironment(): void;
+
+        /** Ends a lexical environment, returning any declarations. */
+        endLexicalEnvironment(): Statement[];
+    }
+
+    /**
+     * Describes an edge of a Node, used when traversing a syntax tree.
+     */
+    interface NodeEdge {
+        /** Indicates that the edge is a NodeArray. */
+        array?: boolean;
+
+        /** Indicates that the result is optional. */
+        optional?: boolean;
+
+        /** A callback used to test whether a node is valid. */
+        test?: (node: Node) => node is Node;
+
+        /** A callback used to lift a NodeArrayNode into a valid node. */
+        lift?: (nodes: NodeArrayNode<Node>) => Node;
+    };
+
+    /**
+     * Describes the shape of a Node.
+     */
+    type NodeTraversalPath = Map<NodeEdge>;
+
+    /**
+     * This map contains information about the shape of each Node in "types.ts" pertaining to how
+     * each node should be traversed during a transformation.
+     *
+     * Each edge corresponds to a property in a Node subtype that should be traversed when visiting
+     * each child. The properties are assigned in the order in which traversal should occur.
+     *
+     * NOTE: This needs to be kept up to date with changes to nodes in "types.ts". Currently, this
+     *       map is not comprehensive. Only node edges relevant to tree transformation are
+     *       currently defined. We may extend this to be more comprehensive, and eventually
+     *       supplant the existing `forEachChild` implementation if performance is not
+     *       significantly impacted.
+     */
+    const nodeEdgeTraversalMap: Map<NodeTraversalPath> = {
+        [SyntaxKind.QualifiedName]: {
+            left: { test: isEntityName },
+            right: { test: isIdentifierNode },
+        },
+        [SyntaxKind.ComputedPropertyName]: {
+            expression: { test: isExpressionNode },
+        },
+        [SyntaxKind.Parameter]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isBindingPatternOrIdentifier },
+            type: { test: isTypeNodeNode, optional: true },
+            initializer: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.Decorator]: {
+            expression: { test: isLeftHandSideExpression },
+        },
+        [SyntaxKind.PropertyDeclaration]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isPropertyName },
+            type: { test: isTypeNodeNode, optional: true },
+            initializer: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.MethodDeclaration]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isPropertyName },
+            typeParameters: { test: isTypeParameter, array: true },
+            parameters: { test: isParameter, array: true },
+            type: { test: isTypeNodeNode, optional: true },
+            body: { test: isBlock, optional: true },
+        },
+        [SyntaxKind.Constructor]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            typeParameters: { test: isTypeParameter, array: true },
+            parameters: { test: isParameter, array: true },
+            type: { test: isTypeNodeNode, optional: true },
+            body: { test: isBlock, optional: true },
+        },
+        [SyntaxKind.GetAccessor]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isPropertyName },
+            typeParameters: { test: isTypeParameter, array: true },
+            parameters: { test: isParameter, array: true },
+            type: { test: isTypeNodeNode, optional: true },
+            body: { test: isBlock, optional: true },
+        },
+        [SyntaxKind.SetAccessor]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isPropertyName },
+            typeParameters: { test: isTypeParameter, array: true },
+            parameters: { test: isParameter, array: true },
+            type: { test: isTypeNodeNode, optional: true },
+            body: { test: isBlock, optional: true },
+        },
+        [SyntaxKind.ObjectBindingPattern]: {
+            elements: { test: isBindingElement, array: true },
+        },
+        [SyntaxKind.ArrayBindingPattern]: {
+            elements: { test: isBindingElement, array: true },
+        },
+        [SyntaxKind.BindingElement]: {
+            propertyName: { test: isPropertyName, optional: true },
+            name: { test: isBindingPatternOrIdentifier },
+            initializer: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.ArrayLiteralExpression]: {
+            elements: { test: isExpressionNode, array: true },
+        },
+        [SyntaxKind.ObjectLiteralExpression]: {
+            properties: { test: isObjectLiteralElement, array: true },
+        },
+        [SyntaxKind.PropertyAccessExpression]: {
+            expression: { test: isLeftHandSideExpression },
+            name: { test: isIdentifierNode },
+        },
+        [SyntaxKind.ElementAccessExpression]: {
+            expression: { test: isLeftHandSideExpression },
+            argumentExpression: { test: isExpressionNode },
+        },
+        [SyntaxKind.CallExpression]: {
+            expression: { test: isLeftHandSideExpression },
+            typeArguments: { test: isTypeNodeNode, array: true },
+            arguments: { test: isExpressionNode, array: true },
+        },
+        [SyntaxKind.NewExpression]: {
+            expression: { test: isLeftHandSideExpression },
+            typeArguments: { test: isTypeNodeNode, array: true },
+            arguments: { test: isExpressionNode, array: true },
+        },
+        [SyntaxKind.TaggedTemplateExpression]: {
+            tag: { test: isLeftHandSideExpression },
+            template: { test: isTemplate },
+        },
+        [SyntaxKind.TypeAssertionExpression]: {
+            type: { test: isTypeNodeNode },
+            expression: { test: isUnaryExpression },
+        },
+        [SyntaxKind.ParenthesizedExpression]: {
+            expression: { test: isExpressionNode },
+        },
+        [SyntaxKind.FunctionExpression]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isIdentifierNode, optional: true },
+            typeParameters: { test: isTypeParameter, array: true },
+            parameters: { test: isParameter, array: true },
+            type: { test: isTypeNodeNode, optional: true },
+            body: { test: isBlock, optional: true },
+        },
+        [SyntaxKind.ArrowFunction]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            typeParameters: { test: isTypeParameter, array: true },
+            parameters: { test: isParameter, array: true },
+            type: { test: isTypeNodeNode, optional: true },
+            body: { test: isConciseBody, lift: liftToBlock },
+        },
+        [SyntaxKind.DeleteExpression]: {
+            expression: { test: isUnaryExpression },
+        },
+        [SyntaxKind.TypeOfExpression]: {
+            expression: { test: isUnaryExpression },
+        },
+        [SyntaxKind.VoidExpression]: {
+            expression: { test: isUnaryExpression },
+        },
+        [SyntaxKind.AwaitExpression]: {
+            expression: { test: isUnaryExpression },
+        },
+        [SyntaxKind.PrefixUnaryExpression]: {
+            operand: { test: isUnaryExpression },
+        },
+        [SyntaxKind.PostfixUnaryExpression]: {
+            operand: { test: isLeftHandSideExpression },
+        },
+        [SyntaxKind.BinaryExpression]: {
+            left: { test: isExpressionNode },
+            right: { test: isExpressionNode },
+        },
+        [SyntaxKind.ConditionalExpression]: {
+            condition: { test: isExpressionNode },
+            whenTrue: { test: isExpressionNode },
+            whenFalse: { test: isExpressionNode },
+        },
+        [SyntaxKind.TemplateExpression]: {
+            head: { test: isTemplateLiteralFragment },
+            templateSpans: { test: isTemplateSpan, array: true },
+        },
+        [SyntaxKind.YieldExpression]: {
+            expression: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.SpreadElementExpression]: {
+            expression: { test: isExpressionNode },
+        },
+        [SyntaxKind.ClassExpression]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isIdentifierNode, optional: true },
+            typeParameters: { test: isTypeParameter, array: true },
+            heritageClauses: { test: isHeritageClause, array: true },
+            members: { test: isClassElement, array: true },
+        },
+        [SyntaxKind.ExpressionWithTypeArguments]: {
+            expression: { test: isLeftHandSideExpression },
+            typeArguments: { test: isTypeNodeNode, array: true },
+        },
+        [SyntaxKind.AsExpression]: {
+            expression: { test: isExpressionNode },
+            type: { test: isTypeNodeNode },
+        },
+        [SyntaxKind.TemplateSpan]: {
+            expression: { test: isExpressionNode },
+            literal: { test: isTemplateLiteralFragment },
+        },
+        [SyntaxKind.Block]: {
+            statements: { test: isStatementNode, array: true },
+        },
+        [SyntaxKind.VariableStatement]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            declarationList: { test: isVariableDeclarationList },
+        },
+        [SyntaxKind.ExpressionStatement]: {
+            expression: { test: isExpressionNode },
+        },
+        [SyntaxKind.IfStatement]: {
+            expression: { test: isExpressionNode },
+            thenStatement: { test: isStatementNode, lift: liftToBlock },
+            elseStatement: { test: isStatementNode, lift: liftToBlock, optional: true},
+        },
+        [SyntaxKind.DoStatement]: {
+            statement: { test: isStatementNode, lift: liftToBlock },
+            expression: { test: isExpressionNode },
+        },
+        [SyntaxKind.WhileStatement]: {
+            expression: { test: isExpressionNode },
+            statement: { test: isStatementNode, lift: liftToBlock },
+        },
+        [SyntaxKind.ForStatement]: {
+            initializer: { test: isExpressionOrVariableDeclarationList, optional: true },
+            condition: { test: isExpressionNode, optional: true },
+            incrementor: { test: isExpressionNode, optional: true },
+            statement: { test: isStatementNode, lift: liftToBlock },
+        },
+        [SyntaxKind.ForInStatement]: {
+            initializer: { test: isExpressionOrVariableDeclarationList },
+            expression: { test: isExpressionNode },
+            statement: { test: isStatementNode, lift: liftToBlock },
+        },
+        [SyntaxKind.ForOfStatement]: {
+            initializer: { test: isExpressionOrVariableDeclarationList },
+            expression: { test: isExpressionNode },
+            statement: { test: isStatementNode, lift: liftToBlock },
+        },
+        [SyntaxKind.ContinueStatement]: {
+            label: { test: isIdentifierNode, optional: true },
+        },
+        [SyntaxKind.BreakStatement]: {
+            label: { test: isIdentifierNode, optional: true },
+        },
+        [SyntaxKind.ReturnStatement]: {
+            expression: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.WithStatement]: {
+            expression: { test: isExpressionNode },
+            statement: { test: isStatementNode, lift: liftToBlock },
+        },
+        [SyntaxKind.SwitchStatement]: {
+            expression: { test: isExpressionNode },
+            caseBlock: { test: isCaseBlock },
+        },
+        [SyntaxKind.LabeledStatement]: {
+            label: { test: isIdentifierNode },
+            statement: { test: isStatementNode, lift: liftToBlock },
+        },
+        [SyntaxKind.ThrowStatement]: {
+            expression: { test: isExpressionNode },
+        },
+        [SyntaxKind.TryStatement]: {
+            tryBlock: { test: isBlock },
+            catchClause: { test: isCatchClause, optional: true },
+            finallyBlock: { test: isBlock, optional: true },
+        },
+        [SyntaxKind.VariableDeclaration]: {
+            name: { test: isBindingPatternOrIdentifier },
+            type: { test: isTypeNodeNode, optional: true },
+            initializer: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.VariableDeclarationList]: {
+            declarations: { test: isVariableDeclaration, array: true },
+        },
+        [SyntaxKind.FunctionDeclaration]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isIdentifierNode, optional: true },
+            typeParameters: { test: isTypeParameter, array: true },
+            parameters: { test: isParameter, array: true },
+            type: { test: isTypeNodeNode, optional: true },
+            body: { test: isBlock, optional: true },
+        },
+        [SyntaxKind.ClassDeclaration]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isIdentifierNode, optional: true },
+            typeParameters: { test: isTypeParameter, array: true },
+            heritageClauses: { test: isHeritageClause, array: true },
+            members: { test: isClassElement, array: true },
+        },
+        [SyntaxKind.EnumDeclaration]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isIdentifierNode },
+            members: { test: isEnumMember, array: true },
+        },
+        [SyntaxKind.ModuleDeclaration]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isModuleName },
+            body: { test: isModuleBody },
+        },
+        [SyntaxKind.ModuleBlock]: {
+            statements: { test: isStatementNode, array: true },
+        },
+        [SyntaxKind.CaseBlock]: {
+            clauses: { test: isCaseOrDefaultClause, array: true },
+        },
+        [SyntaxKind.ImportEqualsDeclaration]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            name: { test: isIdentifierNode },
+            moduleReference: { test: isModuleReference },
+        },
+        [SyntaxKind.ImportDeclaration]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            importClause: { test: isImportClause, optional: true },
+            moduleSpecifier: { test: isExpressionNode },
+        },
+        [SyntaxKind.ImportClause]: {
+            name: { test: isIdentifierNode, optional: true },
+            namedBindings: { test: isNamedImportsOrNamespaceImport, optional: true },
+        },
+        [SyntaxKind.NamespaceImport]: {
+            name: { test: isIdentifierNode },
+        },
+        [SyntaxKind.NamedImports]: {
+            elements: { test: isImportSpecifier, array: true },
+        },
+        [SyntaxKind.ImportSpecifier]: {
+            propertyName: { test: isIdentifierNode, optional: true },
+            name: { test: isIdentifierNode },
+        },
+        [SyntaxKind.ExportAssignment]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            expression: { test: isExpressionNode },
+        },
+        [SyntaxKind.ExportDeclaration]: {
+            decorators: { test: isDecorator, array: true },
+            modifiers: { test: isModifier, array: true },
+            exportClause: { test: isNamedExports, optional: true },
+            moduleSpecifier: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.NamedExports]: {
+            elements: { test: isExportSpecifier, array: true },
+        },
+        [SyntaxKind.ExportSpecifier]: {
+            propertyName: { test: isIdentifierNode, optional: true },
+            name: { test: isIdentifierNode },
+        },
+        [SyntaxKind.ExternalModuleReference]: {
+            expression: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.JsxElement]: {
+            openingElement: { test: isJsxOpeningElement },
+            children: { test: isJsxChild, array: true },
+            closingElement: { test: isJsxClosingElement },
+        },
+        [SyntaxKind.JsxSelfClosingElement]: {
+            tagName: { test: isEntityName },
+            attributes: { test: isJsxAttributeOrJsxSpreadAttribute, array: true },
+        },
+        [SyntaxKind.JsxOpeningElement]: {
+            tagName: { test: isEntityName },
+            attributes: { test: isJsxAttributeOrJsxSpreadAttribute, array: true },
+        },
+        [SyntaxKind.JsxClosingElement]: {
+            tagName: { test: isEntityName },
+        },
+        [SyntaxKind.JsxAttribute]: {
+            name: { test: isIdentifierNode },
+            initializer: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.JsxSpreadAttribute]: {
+            expression: { test: isExpressionNode },
+        },
+        [SyntaxKind.JsxExpression]: {
+            expression: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.CaseClause]: {
+            expression: { test: isExpressionNode },
+            statements: { test: isStatementNode, array: true },
+        },
+        [SyntaxKind.DefaultClause]: {
+            statements: { test: isStatementNode, array: true },
+        },
+        [SyntaxKind.HeritageClause]: {
+            types: { test: isExpressionWithTypeArguments, array: true },
+        },
+        [SyntaxKind.CatchClause]: {
+            variableDeclaration: { test: isVariableDeclaration },
+            block: { test: isBlock },
+        },
+        [SyntaxKind.PropertyAssignment]: {
+            name: { test: isPropertyName },
+            initializer: { test: isExpressionNode },
+        },
+        [SyntaxKind.ShorthandPropertyAssignment]: {
+            name: { test: isIdentifierNode },
+            objectAssignmentInitializer: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.EnumMember]: {
+            name: { test: isPropertyName },
+            initializer: { test: isExpressionNode, optional: true },
+        },
+        [SyntaxKind.SourceFile]: {
+            statements: { test: isStatementNode, array: true },
+        },
+    };
+
+    /**
+     * Similar to `reduceLeft`, performs a reduction against each child of a node.
+     * NOTE: Unlike `forEachChild`, this does *not* visit every node. Only nodes added to the
+     *       `nodeEdgeTraversalMap` above will be visited.
+     *
+     * @param node The node containing the children to reduce.
+     * @param f The callback function
+     * @param initial The initial value to supply to the reduction.
+     */
+    export function reduceEachChild<T>(node: Node, f: (memo: T, node: Node) => T, initial: T) {
+        if (node === undefined) {
+            return undefined;
+        }
+
+        let result = initial;
+        const edgeTraversalPath = nodeEdgeTraversalMap[node.kind];
+        if (edgeTraversalPath) {
+            for (const propertyName in edgeTraversalPath) {
+                const value = (<Map<any>>node)[propertyName];
+                if (value !== undefined) {
+                    const edge = edgeTraversalPath[propertyName];
+                    if (edge.array) {
+                        result = reduceLeft(<NodeArray<Node>>value, f, result);
+                    }
+                    else {
+                        result = f(result, <Node>value);
+                    }
+                }
+            }
+        }
+
+        return result;
+    }
+
+    /**
+     * Visits a Node using the supplied visitor, possibly returning a new Node in its place.
+     *
+     * @param node The Node to visit.
+     * @param visitor The callback used to visit the Node.
+     * @param test A callback to execute to verify the Node is valid.
+     * @param lift A callback to execute to lift a NodeArrayNode into a valid Node.
+     * @param optional A value indicating whether the Node is optional.
+     */
+    export function visitNode<T extends Node>(node: T, visitor: (node: Node) => Node, test?: (node: Node) => boolean, lift?: (node: NodeArrayNode<T>) => T, optional?: boolean): T {
+        if (node === undefined) {
+            return undefined;
+        }
+
+        const visited = visitor(node);
+        if (visited === node) {
+            return node;
+        }
+
+        const lifted = liftNode(visited, lift);
+        if (lifted === undefined) {
+            Debug.assert(optional, "Node not optional.");
+            return undefined;
+        }
+
+        if (test !== undefined) {
+            Debug.assert(test(visited), "Wrong node type after visit.");
+        }
+
+        return <T>visited;
+    }
+
+    /**
+     * Visits a NodeArray using the supplied visitor, possibly returning a new NodeArray in its place.
+     *
+     * @param nodes The NodeArray to visit.
+     * @param visitor The callback used to visit a Node.
+     * @param test A node test to execute for each node.
+     */
+    export function visitNodes<T extends Node, TArray extends NodeArray<T>>(nodes: TArray, visitor: (node: Node) => Node, test?: (node: Node) => boolean): TArray {
+        if (nodes === undefined) {
+            return undefined;
+        }
+
+        let updated: TArray;
+        for (let i = 0, len = nodes.length; i < len; i++) {
+            const node = nodes[i];
+            if (node === undefined) {
+                continue;
+            }
+
+            const visited = visitor(node);
+            if (updated !== undefined || visited === undefined || visited !== node) {
+                if (updated === undefined) {
+                    updated = <TArray>createNodeArray(nodes.slice(0, i), /*location*/ nodes);
+                }
+
+                if (visited === undefined) {
+                    continue;
+                }
+
+                if (isNodeArrayNode<T>(visited)) {
+                    spreadNodeArrayNode(visited, updated, test);
+                }
+                else if (visited !== undefined) {
+                    Debug.assert(test(visited), "Wrong node type after visit.");
+                    updated.push(<T>visited);
+                }
+            }
+        }
+
+        if (updated && isModifiersArray(nodes)) {
+            let flags: NodeFlags = 0;
+            for (const node of updated) {
+                flags |= modifierToFlag(node.kind);
+            }
+
+            (<ModifiersArray><NodeArray<Node>>updated).flags = flags;
+        }
+
+        return updated || nodes;
+    }
+
+    /**
+     * Visits each child of a Node using the supplied visitor, possibly returning a new Node of the same kind in its place.
+     *
+     * @param node The Node whose children will be visited.
+     * @param visitor The callback used to visit each child.
+     * @param environment An optional lexical environment context for the visitor.
+     */
+    export function visitEachChild<T extends Node>(node: T, visitor: (node: Node) => Node, environment?: LexicalEnvironment): T {
+        if (node === undefined) {
+            return undefined;
+        }
+
+        const isNewLexicalEnvironment = environment !== undefined && nodeStartsNewLexicalEnvironment(node);
+        if (isNewLexicalEnvironment) {
+            environment.startLexicalEnvironment();
+        }
+
+        let updated: T & Map<any>;
+        const edgeTraversalPath = nodeEdgeTraversalMap[node.kind];
+        if (edgeTraversalPath) {
+            for (const propertyName in edgeTraversalPath) {
+                const value = (<Map<any>>node)[propertyName];
+                if (value !== undefined) {
+                    const edge = edgeTraversalPath[propertyName];
+                    const visited = visitEdge(edge, value, visitor);
+                    if (updated !== undefined || visited !== value) {
+                        if (updated === undefined) {
+                            updated = cloneNode(node, /*location*/ undefined, node.flags & ~NodeFlags.Modifier, /*parent*/ undefined, /*original*/ node);
+                        }
+
+                        updated[propertyName] = visited;
+                    }
+
+                    if (visited && edge.array && isModifiersArray(<NodeArray<Node>>visited)) {
+                        updated.flags |= (<ModifiersArray>visited).flags;
+                    }
+                }
+            }
+        }
+
+        if (updated === undefined) {
+            updated = node;
+        }
+
+        if (isNewLexicalEnvironment) {
+            const declarations = environment.endLexicalEnvironment();
+            if (declarations !== undefined && declarations.length > 0) {
+                return <T>mergeLexicalEnvironment(updated, declarations, /*nodeIsMutable*/ updated !== node);
+            }
+        }
+
+        return updated;
+    }
+
+    /**
+     * Visits a node edge.
+     *
+     * @param edge The edge of the Node.
+     * @param value The Node or NodeArray value for the edge.
+     * @param visitor A callback used to visit the node.
+     */
+    function visitEdge(edge: NodeEdge, value: Node | NodeArray<Node>, visitor: (node: Node) => Node) {
+        return edge.array
+            ? visitNodes(<NodeArray<Node>>value, visitor, edge.test)
+            : visitNode(<Node>value, visitor, edge.test, edge.lift, edge.optional);
+    }
+
+    /**
+     * Spreads a NodeArrayNode into a NodeArray.
+     *
+     * @param source The source NodeArrayNode.
+     * @param dest The destination NodeArray.
+     * @param test The node test used to validate each node.
+     */
+    function spreadNodeArrayNode<T extends Node>(source: NodeArrayNode<T>, dest: NodeArray<T>, test: (node: Node) => boolean) {
+        for (const element of source) {
+            if (element === undefined) {
+                continue;
+            }
+
+            if (isNodeArrayNode<T>(element)) {
+                spreadNodeArrayNode(element, dest, test);
+            }
+            else {
+                Debug.assert(test === undefined || test(element), "Wrong node type after visit.");
+                dest.push(element);
+            }
+        }
+    }
+
+    /**
+     * Gets a mutable Node for updates, setting the `original` pointer on the Node.
+     */
+    function updateNode<T extends Node>(node: T, flags: NodeFlags) {
+        const updated = cloneNode(node, /*location*/ node, flags, /*parent*/ undefined, /*original*/ node);
+        updated.original = node;
+        return updated;
+    }
+
+    /**
+     * Merge generated declarations of a lexical environment.
+     */
+    function mergeLexicalEnvironment(node: Node, declarations: Statement[], nodeIsMutable: boolean) {
+        const mutableNode = nodeIsMutable ? node : cloneNode(node, /*location*/ node, node.flags, /*parent*/ undefined, /*original*/ node);
+        switch (node.kind) {
+            case SyntaxKind.SourceFile:
+                mergeSourceFileLexicalEnvironment(<SourceFile>mutableNode, declarations);
+                break;
+
+            case SyntaxKind.ModuleDeclaration:
+                mergeModuleDeclarationLexicalEnvironment(<ModuleDeclaration>mutableNode, declarations);
+                break;
+
+            case SyntaxKind.FunctionDeclaration:
+            case SyntaxKind.FunctionExpression:
+            case SyntaxKind.ArrowFunction:
+            case SyntaxKind.MethodDeclaration:
+            case SyntaxKind.GetAccessor:
+            case SyntaxKind.SetAccessor:
+            case SyntaxKind.Constructor:
+                mergeFunctionLikeLexicalEnvironment(<FunctionLikeDeclaration>mutableNode, declarations);
+                break;
+
+            case SyntaxKind.ModuleBlock:
+            case SyntaxKind.Block:
+                mergeBlockLexicalEnvironment(<Block>mutableNode, declarations);
+                break;
+        }
+
+        return mutableNode;
+    }
+
+    /**
+     * Merge generated declarations of a lexical environment into a SourceFile.
+     */
+    function mergeSourceFileLexicalEnvironment(node: SourceFile, declarations: Statement[]) {
+        node.statements = mergeStatements(node.statements, declarations);
+    }
+
+    /**
+     * Merge generated declarations of a lexical environment into a ModuleDeclaration.
+     */
+    function mergeModuleDeclarationLexicalEnvironment(node: ModuleDeclaration, declarations: Statement[]) {
+        Debug.assert(node.body.kind === SyntaxKind.ModuleBlock);
+        node.body = <ModuleBlock>mergeLexicalEnvironment(node.body, declarations, /*nodeIsMutable*/ false);
+    }
+
+    /**
+     * Merge generated declarations of a lexical environment into a FunctionLikeDeclaration.
+     */
+    function mergeFunctionLikeLexicalEnvironment(node: FunctionLikeDeclaration, declarations: Statement[]) {
+        Debug.assert(node.body !== undefined);
+        if (node.body.kind === SyntaxKind.Block) {
+            node.body = <Block>mergeLexicalEnvironment(node.body, declarations, /*nodeIsMutable*/ false);
+        }
+        else {
+            node.body = createBlock([
+                createReturn(<Expression>node.body),
+                ...declarations
+            ]);
+        }
+    }
+
+    /**
+     * Merge generated declarations of a lexical environment into a FunctionBody or ModuleBlock.
+     */
+    function mergeBlockLexicalEnvironment(node: FunctionBody | ModuleBlock, declarations: Statement[]) {
+        node.statements = mergeStatements(node.statements, declarations);
+    }
+
+    /**
+     * Merge generated declarations of a lexical environment into a NodeArray of Statement.
+     */
+    function mergeStatements(statements: NodeArray<Statement>, declarations: Statement[]) {
+        return createNodeArray(statements.concat(declarations), /*location*/ statements);
+    }
+
+    /**
+     * Tries to lift a NodeArrayNode to a Node. This is primarily used to
+     * lift multiple statements into a single Block.
+     *
+     * @param node The visited Node.
+     * @param options Options used to control lift behavior.
+     */
+    function liftNode(node: Node, lifter: (nodes: NodeArrayNode<Node>) => Node): Node {
+        if (node === undefined) {
+            return undefined;
+        }
+        else if (isNodeArrayNode(node)) {
+            const lift = lifter || extractSingleNode;
+            return lift(node);
+        }
+        else {
+            return node;
+        }
+    }
+
+    /**
+     * Lifts a NodeArray containing only Statement nodes to a block.
+     *
+     * @param nodes The NodeArray.
+     */
+    function liftToBlock(nodes: NodeArray<Node>) {
+        Debug.assert(trueForAll(nodes, isStatementNode), "Cannot lift nodes to a Block.");
+        return createBlock(<NodeArray<Statement>>nodes);
+    }
+
+    /**
+     * Extracts the single node from a NodeArray.
+     *
+     * @param nodes The NodeArray.
+     */
+    function extractSingleNode(nodes: NodeArray<Node>) {
+        Debug.assert(nodes.length <= 1, "Too many nodes written to output.");
+        return nodes.length > 0 ? nodes[0] : undefined;
+    }
+}
\ No newline at end of file