How does Menhir's option() work?

Learning
1

I’m writing an Objective-C parser with Menhir and cannot figure out why the following rule

| CARET; t = option(LPAREN s=IDENT ASTERISK? RPAREN { s })
LPAREN l = separated_list(COMMA, t=IDENT ASTERISK* s=IDENT { (t, s) }) RPAREN
LBLOCK; b = statement* RBLOCK { Block (t, l, b) }

matches

^(NSString *)(ClassA *objA, ClassB *objB) {

}

and doesn’t match

^(ClassA *objA, ClassB *objB) {

}

Can you please point out the error in my understanding of option()?

2

It should work as you wrote it. But it’s kind of hard to understand without a bit more context. When you say doesn’t match, is it that you get a syntax error or is the phrase parsed by some other rule (which would be a conflict that was arbitrarily resolved in favor of that rule ?).
And if you print your tokens as they are lexed, do you see them in the right order ?

3

Actually scratch that, I tested the rule and indeed there is a conflict, when seing the first LPAREN,
the parser cannot decide which rule should apply (unfold the option, or skip it and start the rest of the rule).

4

Not tested but it looks like a case where using ioption could help ?

5

Indeed it works with ioption (for a grammar with just the single rule in the original question).

6

Yes, in this case inlining solves the problem. Thanks for your prompt help :man_bowing: