Eval

- Added support for compiled expressions that are compiled once and
  evaluated multiple times in different contexts.

src/Eval.h

@@ -44,6 +44,8 @@ public:
   void addSource (bool (*fn)(const std::string&, Variant&));
   void evaluateInfixExpression (const std::string&, Variant&) const;
   void evaluatePostfixExpression (const std::string&, Variant&) const;
+  void compileExpression (const std::string&);
+  void evaluateCompiledExpression (Variant&);
   void ambiguity (bool);
   void debug ();
 
@@ -69,6 +71,7 @@ private:
   std::vector <bool (*)(const std::string&, Variant&)> _sources;
   bool _ambiguity;
   bool _debug;
+  std::vector <std::pair <std::string, Lexer::Type> > _compiled;
 };