public override Value Handle(Expression left, Expression right, IDictionary<String, Value> symbols)
{
var l = left.Interpret(symbols);
var r = new StringValue(End) as Value;
var symbol = right as SymbolExpression;
if (symbol == null || !symbol.SymbolName.Equals(End))
{
r = right.Interpret(symbols);
}
return Perform(l, r);
}