diff --git a/lesscpy/plib/deferred.py b/lesscpy/plib/deferred.py
index e20658b..c8a9145 100644
--- a/lesscpy/plib/deferred.py
+++ b/lesscpy/plib/deferred.py
@@ -29,12 +29,16 @@ class Deferred(Node):
         returns:
             mixed
         """
+        args = [p.parse(scope) 
+                if hasattr(p, 'parse')
+                else p
+                for p in self.args]
         if hasattr(self.mixin, 'call'):
-            return self.mixin.call(scope, self.args)
+            return self.mixin.call(scope, args)
         mixins = scope.mixins(self.mixin.raw())
         if not mixins: return mixins
         for mixin in mixins:
-            res = mixin.call(scope, self.args)
+            res = mixin.call(scope, args)
             if res: 
                 return res
         return False
diff --git a/lesscpy/plib/expression.py b/lesscpy/plib/expression.py
index 12f549e..e144cfb 100644
--- a/lesscpy/plib/expression.py
+++ b/lesscpy/plib/expression.py
@@ -77,7 +77,7 @@ class Expression(Node):
         returns:
             str
         """
-        if not val: return val
+        if not val: return str(val)
         if ua or ub:
             if ua and ub:
                 if ua == ub:
@@ -88,7 +88,7 @@ class Expression(Node):
                 return str(val) + ua
             elif ub:
                 return str(val) + ub
-        return val
+        return str(val)
     
     def operate(self, vala, valb, oper):
         """Perform operation
diff --git a/lesscpy/plib/string.py b/lesscpy/plib/string.py
index b106753..5c25fa0 100644
--- a/lesscpy/plib/string.py
+++ b/lesscpy/plib/string.py
@@ -33,7 +33,7 @@ class String(Node):
         returns:
             str
         """
-        var = '@' + var
-        var = ''.join(utility.flatten(self.scope.swap(var)))
+        var = self.scope.swap('@' + var)
+        var = ''.join(utility.flatten(var))
         return var.strip("\"'")
     
\ No newline at end of file
diff --git a/lesscpy/test/testexpression.py b/lesscpy/test/testexpression.py
index 12b0e9f..46566bc 100644
--- a/lesscpy/test/testexpression.py
+++ b/lesscpy/test/testexpression.py
@@ -6,14 +6,14 @@ from lesscpy.plib.expression import Expression
 class TestExpression(unittest.TestCase):        
     def test_basic(self):
         for test in [
-            ['0', '+', '0', 0],
-            ['2', '+', '2', 4],
-            ['2.0', '+', '2', 4.0],
-            ['2', '+', '2.0', 4.0],
-            ['2.0', '+', '2.0', 4.0],
-            [('2.0',), '+', '2.0', 4.0],
-            [('2.0',), '+', ('2.0',), 4.0],
-            ['0px', '+', '0', 0],
+            ['0', '+', '0', '0'],
+            ['2', '+', '2', '4'],
+            ['2.0', '+', '2', '4.0'],
+            ['2', '+', '2.0', '4.0'],
+            ['2.0', '+', '2.0', '4.0'],
+            [('2.0',), '+', '2.0', '4.0'],
+            [('2.0',), '+', ('2.0',), '4.0'],
+            ['0px', '+', '0', '0'],
             ['2px', '+', '2', '4px'],
             ['2.0px', '+', '2', '4.0px'],
             [('2px', ' '), '+', '2.0', '4.0px'],
@@ -24,17 +24,17 @@ class TestExpression(unittest.TestCase):
             
     def test_neg(self):
         for test in [
-            ['-0', '+', '0', 0],
-            ['-2', '+', '-2', -4],
-            ['-2.0', '+', '-2', -4.0],
-            ['-2', '+', '-2.0', -4.0],
-            ['-2.0', '+', '-2.0', -4.0],
-            ['-0', '-', '0', 0],
-            ['-2', '-', '-2', 0],
-            ['-2.0', '-', '2', -4.0],
-            ['-2', '-', '-2.0', 0],
-            ['2.0', '-', '-2.0', 4.0],
-            ['-0px', '+', '0', 0],
+            ['-0', '+', '0', '0'],
+            ['-2', '+', '-2', '-4'],
+            ['-2.0', '+', '-2', '-4.0'],
+            ['-2', '+', '-2.0', '-4.0'],
+            ['-2.0', '+', '-2.0', '-4.0'],
+            ['-0', '-', '0', '0'],
+            ['-2', '-', '-2', '0'],
+            ['-2.0', '-', '2', '-4.0'],
+            ['-2', '-', '-2.0', '0.0'],
+            ['2.0', '-', '-2.0', '4.0'],
+            ['-0px', '+', '0', '0'],
             ['-2px', '+', '-2', '-4px'],
             ['-2.0', '+', '-2px', '-4.0px'],
             ['-2em', '+', '-2.0', '-4.0em'],