what is the return value type to replace the auto obscure

[jojogh]

I want to write a small expression compiler by using boost spirit x3 and yap. The idea are like these:

1. Write a parser to parser the syntax into an AST;
2. Than compile the ast into the expression, like A = B(a,b) + C(a,b) - 1.2;
3. When needed, pass the expression to where it is needed, and use yap evaluate to get the result.

Following is my code to implement some ideas. However, i met a problem in the eval struct operator, like following. I just want to know if i use this pattern, what exactly the return value is(not auto), to adapt plus and minus expression template? thanks.....

        auto operator()(operation const& x,int rhs, int lhs) const
        {
            //int rhs = boost::apply_visitor(*this, x.operand_);
            auto rhs_w = boost::yap::make_terminal<tarray_expr>(rhs);
            auto lhs_w = boost::yap::make_terminal<tarray_expr>(lhs);
            switch (x.operator_)
            {
            case '+': return lhs_w + rhs_w;
            case '-': return lhs_w - rhs_w;
            }
            //return rhs;
        }

I re-editted the post, and attached the code as a txt file, and looking forward for the help, thanks! main.cpp.txt

[tzlaine]

This is really for bug reporting, not advice. However, at least one of the YAP examples will probably help; you should start there.