diff --git a/src/js/app/bitwise/calc.js b/src/js/app/bitwise/calc.js
index 385ccbc..85f7f47 100644
--- a/src/js/app/bitwise/calc.js
+++ b/src/js/app/bitwise/calc.js
@@ -24,7 +24,7 @@ app.set('calc', function() {
         },
 
         calcExpression: function (expr) {
-            return eval(expr.string);
+            return eval(expr.expressionString);
         }
     }
 });
\ No newline at end of file
diff --git a/src/js/app/bitwise/expression.js b/src/js/app/bitwise/expression.js
index ffc70a5..493ca07 100644
--- a/src/js/app/bitwise/expression.js
+++ b/src/js/app/bitwise/expression.js
@@ -5,7 +5,7 @@ app.set('expression', function() {
     var listRegex = /^(-?(?:\d+|0x[\d,a-f]+)\s?)+$/;
     var notRex = /^(~)(-?(?:\d+|0x[\d,a-f]+))$/;
 
-    return {
+    var expression = {
         canParse: function(string) {
             return exprRegex.test(string) || listRegex.test(string) || notRex.test(string)
         },
@@ -39,40 +39,36 @@ app.set('expression', function() {
             }
 
             return new Operand(str);
-        }
-
+        },
+        TwoOperandExpression: TwoOperandExpression,
+        SingleOperandExpression: SingleOperandExpression,
+        ListOfNumbersExpression: ListOfNumbersExpression
     };
 
     function createTwoOperandExpr(matches) {
 
-        var m = new app.models.BitwiseOperation();
-        m.operand1 = new Operand(matches[1]);
-        m.operand2 = new Operand(matches[3]);
-        m.sign = matches[2];
-        m.string = matches.input;
-        //m.result = eval(matches.input);
+        var operand1 = new Operand(matches[1]),
+            operand2 = new Operand(matches[3]),
+            sign = matches[2],
+            expressionString = matches.input;
 
-        return m;
+        return new TwoOperandExpression(expressionString, operand1, operand2, sign);
     }
 
     function createSingleOperandExpr(matches) {
-        var m = new app.models.BitwiseOperation();
-        m.operand1 = new Operand(matches[2]);
-        m.sign = matches[1];
-        m.string = matches.input;
-        return m;
+        var operand = new Operand(matches[2])
+        return new SingleOperandExpression(matches.input, operand, matches[1]);
     }
 
     function createListOfNumbersExpression(input) {
-        var operands = [];
+        var numbers = [];
         input.split(' ').forEach(function(n){
             if(n.trim().length > 0) {
-                operands.push(new Operand(n.trim()));
+                numbers.push(new Operand(n.trim()));
             }
-
         });
 
-        return new app.models.BitwiseNumbers(operands);
+        return new ListOfNumbersExpression(input, numbers);
     }
 
     function getBase(kind) {
@@ -97,4 +93,35 @@ app.set('expression', function() {
         this.kind = this.input.indexOf('0x') > -1 ? 'hex' : 'dec';
         this.other = this.kind == 'dec' ? this.hex : this.dec;
     }
+
+    function SingleOperandExpression(expressionString, operand, sign) {
+        this.expressionString = expressionString;
+        this.operand1 = operand;
+        this.sign = sign;
+    }
+
+    function TwoOperandExpression(expressionString, operand1, operand2, sign) {
+        this.expressionString = expressionString;
+        this.operand1 = operand1;
+        this.operand2 = operand2;
+        this.sign = sign;
+    }
+
+    function ListOfNumbersExpression(expressionString, numbers) {
+        this.expressionString = expressionString;
+        this.numbers = numbers;
+    }
+
+    function Expression() {
+    }
+
+    Expression.prototype.toString = function() {
+        return this.expressionString ? "Expression: " + this.expressionString : this.toString();
+    };
+
+    //TwoOperandExpression.prototype = Expression.prototype;
+    //SingleOperandExpression.prototype = Expression.prototype;
+    //ListOfNumbersExpression.prototype = Expression.prototype;
+
+    return expression;
 });
\ No newline at end of file
diff --git a/src/js/app/cmd/commands.js b/src/js/app/cmd/commands.js
index ac83341..6ae4839 100644
--- a/src/js/app/cmd/commands.js
+++ b/src/js/app/cmd/commands.js
@@ -4,6 +4,7 @@ app.run(function() {
     var cmd = app.get('cmd');
     var cmdConfig = app.get('cmdConfig');
     var rootView = app.get('rootView');
+    var expression = app.get('expression');
 
     cmd.commands({
         'help': function() {
@@ -36,6 +37,7 @@ app.run(function() {
         },
         '-debug': function() {
             app.debugMode = true;
+            console.log('debug is on');
         },
         '-notrack': function () {}
     });
@@ -44,7 +46,19 @@ app.run(function() {
     cmd.command({
         canHandle: function(input) { return app.get('expression').canParse(input); },
         handle: function(input) {
-            return app.get('expression').parse(input);
+            var expr = expression.parse(input);
+            return this.locateModel(expr);
+        },
+        locateModel: function (expr) {
+            if(expr instanceof expression.SingleOperandExpression || expr instanceof expression.TwoOperandExpression){
+                return new app.models.BitwiseOperation(expr);
+            }
+
+            if(expr instanceof expression.ListOfNumbersExpression) {
+                return new app.models.BitwiseNumbers(expr);
+            }
+
+            return new app.models.ErrorResult('Cannot create model for expression: ' + expr.toString());
         }
     });
 
diff --git a/src/js/app/modelViews.js b/src/js/app/modelViews.js
index 7197ea6..acd7155 100644
--- a/src/js/app/modelViews.js
+++ b/src/js/app/modelViews.js
@@ -29,12 +29,12 @@ app.compose(function () {
         }
 
         return {
-            renderView: function(expr) {
+            renderView: function(model) {
                 // TODO: move all this to expression
-                var result = expression.createOperand(calc.calcExpression(expr), getResultMode([expr.operand1, expr.operand2]));
-                var maxLen = getBinaryLength([expr.operand1.value, expr.operand2 != null ? expr.operand2.value : 0, result.value]);
+                var result = expression.createOperand(calc.calcExpression(model.expression), getResultMode([model.operand1, model.operand2]));
+                var maxLen = getBinaryLength([model.operand1.value, model.operand2 != null ? model.operand2.value : 0, result.value]);
 
-                var model = Object.create(expr);
+                var model = Object.create(model);
                 model.bitsSize = maxLen;
                 model.result = result;
 
diff --git a/src/js/app/models.js b/src/js/app/models.js
index 1627aab..0ebc5c9 100644
--- a/src/js/app/models.js
+++ b/src/js/app/models.js
@@ -1,18 +1,21 @@
 (function(app) {
     "use strict";
 
-    function BitwiseOperation () {
+    function BitwiseOperation (expression) {
+        this.expression = expression;
+        this.operand1 = expression.operand1;
+        this.operand2 = expression.operand2;
+        this.sign = expression.sign;
+        this.string = expression.expressionString;
     }
 
-    BitwiseOperation.prototype.calculate = function () {
-        return eval(this.string);
-    };
+    function BitwiseNumbers(expression) {
+        this.expression = expression;
+        this.operands = expression.numbers;
 
-    function BitwiseNumbers(operands) {
-        this.operands = operands;
         var numbers = this.numbers = [];
 
-        operands.forEach(function (o) {
+        expression.numbers.forEach(function (o) {
            numbers.push(o.value);
         });
     }
diff --git a/src/js/core/di.js b/src/js/core/di.js
index ed0cb9a..1c064f7 100644
--- a/src/js/core/di.js
+++ b/src/js/core/di.js
@@ -35,7 +35,7 @@
 
     function resolveInternal(name) {
         if(contains(this.resolutionStack, name)) {
-            throw new Error("Failed to resolve service: " + name + ". Circular reference: " + this.resolutionStack.join(' < '));
+            throw new Error("Failed to resolve dependency: " + name + ". Circular reference: " + this.resolutionStack.join(' < '));
         }
 
         this.resolutionStack.unshift(name);
diff --git a/tests/unit/domain/expressionSpec.js b/tests/unit/domain/expressionSpec.js
index 7dfb5d4..9b89ddd 100644
--- a/tests/unit/domain/expressionSpec.js
+++ b/tests/unit/domain/expressionSpec.js
@@ -41,7 +41,8 @@ describe("expression parse", function() {
                 expect(actual.operand2).not.toBeDefined();
             }
 
-            expect(actual.string).toBe(expected.string);
+            expect(actual.expressionString).toBe(expected.string);
+            console.log(actual.toString());
         }
     });
 
@@ -59,7 +60,8 @@ describe("expression parse", function() {
             var expected = listCases[input];
 
             for(i =0; i<expected.length;i++) {
-                expect(actual.operands[i].value).toBe(expected[i]);
+                expect(actual.numbers[i].value).toBe(expected[i]);
+                expect(actual.expressionString).toBe(input)
             }
         }
     });