better boolean handling..

still T symbol should be implemented

ml.h

@@ -110,6 +110,9 @@ public:
     // Constructs a floating point value
     MlValue(double f);
 
+    // Constructs a bool value
+    MlValue(bool b);
+
     // Constructs a list
     MlValue(const std::vector<MlValue> &list);