Dynamically create OR list for parser rule

[dhowe]

Greetings,
So I currently have a parser rule like this:

    $.RULE("atom", () => {
      $.OR([
         { ALT: () => $.SUBRULE($.type1) },
         { ALT: () => $.SUBRULE($.type2) },
         { ALT: () => $.SUBRULE($.type3) },
          ... 
         { ALT: () => $.SUBRULE($.typeN) },
      ])
    });

that I would instead like to construct dynamically as follows:

    $.RULE("atom", () => {
      $.OR(ruleTypes.map(t => { ALT: () => $.SUBRULE($[t]) }))
    });

Is this possible given how the grammar recording works? Currently I get the error:
TypeError: Cannot read properties of undefined (reading 'RULE') This error was thrown during the "grammar recording phase"...

thanks!

[msujew]

We do something similar in Langium where we generate a Chevrotain parser/grammar from a DSL grammar definition (see code). So it should definitely be possible to create (partially) dynamic grammars.

However, I'm a bit confused by the error message you're encountering here. It sounds like you're calling $.RULE(...) without defining $ first. I don't believe anything else calls RULE except user code. Can you share a reproducible example?

[dhowe]

I also found that confusing -- the actual message is as follows (I was trying unsuccessfully to simplify the question): TypeError: Cannot read properties of undefined (reading 'GATE')

I do have a rule named 'gate', and a token called 'Gate', but no reference in the code to 'GATE':

[msujew]

Again, difficult to guess what the issue is without seeing the full code. Can you share a reproducible example?

However, the error hints that one of the alternatives that you pass to OR is undefined (GATE is a property on the alternatives passed to OR).

[dhowe]

The error ended up being rather trivial (missing parens when returning an object from an anonymous function), but the error message made it a bit hard to track down. The code (now working as expected) is:

 $.RULE("atom", () => {
   $.OR(ruleTypes.map(t => ({ ALT: () => $.SUBRULE($[t]) })))
 });

thanks for the help @msujew