How to say "one or more of a few options" in parser?

[dhowe]

I'm sure this is super obvious (I'm a new user), but how to define a parser rule that says one or more of a few options:

element: 
  (chars | choice | symbol)+;

Is the proper way to create a sub-rule for each option (as below,) or can I simply say AT_LEAST_ONE(OR [{ALT: ..., }])

   $.RULE("element-part", () => {
      $.OR([
        { ALT: () => $.SUBRULE($.chars) },
        { ALT: () => $.SUBRULE($.choice) },
        { ALT: () => $.SUBRULE($.symbol) },
      ])
    })

    $.RULE("element", () => {
      $.AT_LEAST_ONE(() => $.SUBRULE($.element-part"));
    });

[msujew]

Hey @dhowe, I've converted this into an discussions, since they are better suited for asking and answering questions on GitHub.

or can I simply say AT_LEAST_ONE(OR [{ALT: ..., }])

Yes, everything in Chevrotain is embeddable into each other. In your case it would be:

$.RULE("element", () => {
  $.AT_LEAST_ONE(() => 
    $.OR([
      { ALT: () => $.SUBRULE($.chars) },
      { ALT: () => $.SUBRULE($.choice) },
      { ALT: () => $.SUBRULE($.symbol) },
    ])
  ));
});

[dhowe]

thanks @msujew - ended up with something quite similar... now trying to figure out why some of these subrules never fire

does the order of subrules matter?

[msujew]

Yes, the order is important. Chevrotain will always pick the first option that fits your input. For example if you have such a grammar:

Rule: 'a' | 'a' 'b';

Chevrotain will only ever pick the first alternative, since it's the first that matches the input a b.