Antlr4-JS actions in grammar: how to access tokens and define funcs ? (direct in java, not in JS)

问题

I'm trying to adapt to JS target the Expr.g4 of the book. In this example, actions are directly in the grammar. They include utility functions defined in @parser::members , that are called in the rules.

The example works well in Java, but in its JS translation I have 2 problem: - getting the action function visible by the action rule - getting the tokens recognized in the function.

I finally manage to get this working formulation:

@parser::members {

  myeval =  function(left, op, right) {
        switch ( op ) {
            case Expr_jsParser.MUL : return left * right;
            case Expr_jsParser.DIV : return left / right;
            case Expr_jsParser.ADD : return left + right;
            case Expr_jsParser.SUB : return left - right;
        }
        return 0;
    };
}

( myeval is the action function. MUL, DIV, etc are the grammar tokens. Expr_jsParser is a class generated by Antlr) I'm pretty sure there is a cleaner way to do this, isn't it ?

回答1:

Eric Vergnaud (the JS guy of Antlr) tells me that it's the regular behavior. Simply, java accept skipping the prefix while JS does not.

来源：https://stackoverflow.com/questions/31296258/antlr4-js-actions-in-grammar-how-to-access-tokens-and-define-funcs-direct-in