diff --git a/lib/index.html b/lib/index.html
index f369a916..c3ea700e 100644
--- a/lib/index.html
+++ b/lib/index.html
@@ -13,6 +13,7 @@
         <script src="./mozilla-ast.js"></script>
         <script src="./translate.js"></script>
         <script src="./std.js"></script>
+        <script src="./typecheck.js"></script>
     	<style>
     	
     	body {
@@ -295,7 +296,7 @@ main();</textarea>
 			return stream.toString();
 		}
 
-        function Mangle(){
+        function Test(){
             var ast;
 
             try {
@@ -304,7 +305,7 @@ main();</textarea>
                 if(!isjs.checked) ast = ast.toJavaScript({ main_binding : mainbinding.checked });
 
                 // 3. mangle
-                //ast.figure_out_scope();
+                ast.figure_out_scope();
                 //ast.compute_char_frequency();
                 //ast.mangle_names({ sort : true, toplevel : true });
 
diff --git a/lib/typecheck.js b/lib/typecheck.js
index 7c73ee35..83452867 100644
--- a/lib/typecheck.js
+++ b/lib/typecheck.js
@@ -51,9 +51,9 @@
         * AST_SymbolFunarg
 
     Levels of follow:
-        1 level:    Simple types: String, Number, Boolean, Function.
-        2 level:    Arrays and Object ( Array<val_type>, Array<key_type, val_type> ).
-        Deep-level: interfaces, classes, singletones.
+        1 level: Simple types: String, Number, Boolean, Function.
+        2 level: Arrays and Object ( Array<val_type>, Array<key_type, val_type> ).
+        Deep   : interfaces, classes (prototypes), singletones.
 
     Operations to check:
         * AST_Return
@@ -63,4 +63,152 @@
         * AST_Binary
         * AST_Conditional
         * AST_Assign
-*/
\ No newline at end of file
+
+    Warnings:
+        * type mismatch
+        * redefinition of variable
+*/
+
+
+// TypedObject
+
+Cola.TypedObject = function (name, vartype, isfunc) {
+    this.name = name;
+    this.vartype = vartype;
+    this.isfunc = isfunc;
+};
+
+
+// TypeStorage
+
+Cola.TypeStorage = function (parentStorage) {
+    this.parentStorage = parentStorage;
+    this.objs = [];
+};
+
+Cola.TypeStorage.prototype.contains = function (name, isfunc) {
+    return this.objs.some(function(el){
+        return el.name == name && el.isfunc == isfunc;
+    });
+};
+
+Cola.TypeStorage.prototype.remove = function (name, isfunc) {
+    var pre = this.objs.length;
+    this.objs = this.objs.filter(function(el){
+        return !(el.name == name && el.isfunc == isfunc);
+    });
+
+    return pre != this.objs.length;
+};
+
+Cola.TypeStorage.prototype.uniqueAdd = function (name, vartype, isfunc) {
+    if(!this.contains(name, isfunc)){
+        this.objs.push(new Cola.TypedObject(name, vartype, isfunc));
+        return true;
+    }
+
+    return false;
+};
+
+Cola.TypeStorage.prototype.owerwriteAdd = function (name, vartype, isfunc) {
+    var removed = this.remove(name, isfunc);
+    this.objs.push(new Cola.TypedObject(name, vartype, isfunc));
+    return removed;
+};
+
+Cola.TypeStorage.prototype.get = function (name) {
+    var obj = false;
+    this.objs.some(function(el){
+        return el.name == name && (obj = el);
+    });
+
+    if(!obj && this.parentStorage) obj = this.parentStorage.get(name);
+};
+
+
+// TypeChecker
+ 
+Cola.TypeChecker = function (parentStorage, om) {
+    this.outputMode = om == undefined ? Cola.TypeChecker.WARNING : om;
+    this.storage = new Cola.TypeStorage(parentStorage, this.outputMode);
+};
+
+Cola.TypeChecker.prototype.reg = function (def) {
+    if(def.forEach) def.forEach(function(d){
+        if(d instanceof Cola.AST_VarDef && !this.storage.uniqueAdd(d.name.name, d.type, false)){
+            this.printVarRedef(d.name.start);
+            this.storage.owerwriteAdd(d.name.name, d.type, false);
+        } else 
+        if(d instanceof Cola.AST_SymbolFunarg) this.storage.owerwriteAdd(d.name, d.type, false);
+    }, this); else 
+    if(def instanceof Cola.AST_Defun){
+        if(!this.storage.uniqueAdd(def.name.name, "Function", false)){
+            this.printFuncRedef(def.start);
+            this.storage.owerwriteAdd(def.name.name, "Function", false);
+        } 
+        this.storage.owerwriteAdd(def.name.name, def.type, true);
+    }
+};
+
+Cola.TypeChecker.prototype.printMessage = function (token, msg) {
+    switch(this.outputMode){
+        case Cola.TypeChecker.WARNING:
+            console.warn("TypeWarning: " + msg)
+            break;
+        case Cola.TypeChecker.ERROR:
+            throw new TypeError(msg);
+    }
+};
+
+Cola.TypeChecker.prototype.printMism = function (token) {
+    this.printMessage(token, "type mismatch (line: " + token.line + ", col: " + token.col + ", pos: " + token.pos + ")");
+    
+};
+
+Cola.TypeChecker.prototype.printVarRedef = function (token) {
+    this.printMessage(token, "redefinition of variable (line: " + token.line + ", col: " + token.col + ", pos: " + token.pos + ")");
+};
+
+Cola.TypeChecker.prototype.printFuncRedef = function (token) {
+    this.printMessage(token, "redefinition of function (line: " + token.line + ", col: " + token.col + ", pos: " + token.pos + ")");
+};
+
+Cola.TypeChecker.WARNING = 0;
+Cola.TypeChecker.ERROR   = 1;
+Cola.TypeChecker.SILENT  = 2;
+
+
+// Checker function
+
+Cola.AST_Toplevel.DEFMETHOD("check_types", function(options){
+    options = Cola.defaults(options, {
+        output_mode: Cola.TypeChecker.WARNING
+    });
+
+    var currScope = null, csDump = null,
+    tw = new Cola.TreeWalker(function(node, descend){
+
+        if (node instanceof Cola.AST_Scope) {
+            node.type_checker = new Cola.TypeChecker(node.parent_scope ? node.parent_scope.type_checker.storage : null, options.output_mode);
+
+            if (node instanceof Cola.AST_Defun) currScope.type_checker.reg(node);
+            if (node instanceof Cola.AST_Function || node instanceof Cola.AST_Defun) node.type_checker.reg(node.argnames);
+
+            csDump = currScope;
+            currScope = node;
+            descend();
+            currScope = csDump;
+
+            return true;
+        }
+
+        if (node instanceof Cola.AST_Var) 
+            currScope.type_checker.reg(node.definitions);
+        //else
+
+        //if ()
+
+        descend();
+    });
+    this.walk(tw);
+});