How to solve ambiguity in an expression like new Date().getTime()?

Question

We are working on a new version of a JavaScript grammar using Rascal. Based on the language specification (version 6) and existing JavaScript grammars, the following are valid productions for expressions:

syntax Expression = ... 
                  | new: "new" Expression
                  | call: Expression Args

syntax Args = ...

However, when we try to parse an expression like "new Date().getTime()" we get an Ambiguity error. We tried to fix it using a combination of the "left" and ">" operators, something like

| left "new" Expression
> Expression Args

but we were not able to fix the problem. I believe that this might be simple to solve, but after spending a couple of hours, we could not figure out a solution.

I'd be interested to find what you've learned about the priority mechanism from this. Perhaps we might improve docs or the warnings of the new static checker. Pls email? — Jurgen Vinju, Jan 10 '19 at 07:00

score 1 · Accepted Answer · answered Jan 09 '19 at 20:38

I've tried to complete your example here, and this works without throwing an Ambiguity() exception.

module Test

import IO;
import ParseTree;

lexical Ident = [A-Za-z]+ !>> [a-zA-Z];
layout Whitespace = [\t\n\r\ ]*;

syntax Expression 
  = Ident
  | "new" Expression
  > Expression "(" {Expression ","}* ")"
  > right Expression "." Expression
  ;

void main() {
  Expression ex = parse(#Expression, "a().b()");
  println(ex);

  Expression ex2 = parse(#Expression, "new a().b()");
  println(ex2);
}

How to solve ambiguity in an expression like new Date().getTime()?

1 Answers1