public static Invokee ToEvaluator(this FP.Expression expr, SymbolTable scope)
        {
            var compiler = new EvaluatorVisitor();

            return(expr.Accept <Invokee>(compiler, scope));
        }
        public static string Dump(this Expression expr)
        {
            var dumper = new TreeVisualizerVisitor();

            return(expr.Accept(dumper, new SymbolTable()).ToString());
        }