Bison C++ Syntax

[Hans Aberg]

I have a suggest for future Bison C++ user interface. I once wrote a parser
by hand, and developed the syntax in that context. I also just made a
working example with Bison compiled as C++ and the Flex C++ class it can
generate.

Then the use is like this (skipping namespace for now), when the parser is
a small calculator that reads a single line, and one wants to put it into a
REP (read-evaluate-print) loop:

int main() {
    Parser calculator; // Could have arguments.
    double d;

    while (cin) {
        try {
            std::cin >> calculator >> d; // Parser can be used as manipulator.
            std::cout << d << endl;
        }
        catch (Exit& ex) {   // Parser exits by throwing an Exit exception.
            std::cout << ex.what() << endl;
            return ex.status();
        }
    }

    return EXIT_SUCCESS;
}

The class Parse can also have various functions that allows the user to
manipulate it, for example Parser::reset(), and such functions.

I have found this manipulator syntax very efficient, because it is easy to
use; the user does not need to know much in order to get it up and working:

My example calculator exits by that one types "exit", and it does error
recovery, so it is rather self-contained. It would be easy to flip it into
any other standard program that wants to read a double, if one instead
wants to allow full arithmetical expressions in input. So it is extremely
easy to use this syntax in order to enhance already existing C++ programs
that are in the need of a more advanced parsed input.

  Hans Aberg