PEG.js: how to use prompt?

Question

I'm creating a C++ parser with PEG.js, and I need to be able to use cin . With the after-match JS, when I use prompt() , the (alternate) online version throws an error of 'Parse Error: prompt is not defined'. I am trying to use the initializer to create a function to replicate prompt (probably not optimized, I was just trying it as a solution). However, when I do this, it still gives me the error. I have tried using window.prompt as well, but again, it does not work. Here's an example of what I'm doing:

{
    function cin() {
        window.prompt("");
    }

    function changeVar(variable, newValue) {
        if(typeof variable === typeof newValue) {
            variable = newValue;
        } else if(typeof variable === 'undefined') {
            alert("You can't assign a value to a variable if the variable isn't declared yet!");
        } else {
            alert("Bad assignment. In C++, a variable *must* have the same type *all the time*.");
        }
    }
}

stdin =
    whitespace* "std::cin" whitespace* ">>" whitespace* varToBeChanged:[a-zA-Z_]+ ";" whitespace*
        { changeVar(varToBeChanged, cin('')); return varToBeChanged; }

whitespace =
    space:[ \t]
        { return space; }

and then in the parser testing field:

std::cin >> variable;

Thank you for looking. I have tried Googling this and SO-searching this but I haven't found any results.

Also, here is the main piece of code , for all the (current) extra information anyone needs. I am having some problems with this as well, but I'll try to figure them out on my own before I post another question.

Answer 1

If you are using http://peg.arcanis.fr/ , then the parser code is executed inside of a Web Worker - which has no access to any UI like the window or the DOM. The error " undefined variable " means literally that there is no window or prompt declared.

If you paste your code into http://pegjs.majda.cz/online , it is executed in the web page environment and works flawlessly.