Hello! It becomes clear now that I have some problems in speaking my thoughts :)

the failure of an optional subrule means that it is not present

That is the way Parse::RecDescent thinks of it indeed. But from a human point of view we can say that failure of a rule can also mean that it IS present but contains some errors that prevent it from matching. And using a <commit> directive is a good way to inform the parser that "This production is present, I'm sure of it. If it will not match then it apparently contains an error, and you should fail without trying other alternatives as they will not match a fortiori". The only problem with <commit> is that it only works on other productions of the same rule and has no effect on subrules. That trick in FAQ is a try to extend the power of <commit> on subrule calls.

You are now saying, as I think you always intended to be saying, that the grammar must match one of the available alternatives, or declare that an error has occurred. I do not think that you actually mean for the rule to be “optional” at all

I'm sorry for my question being so ambiguous. Once again, as you can see in FAQ, that is not a try to question mysubrule's optionality but to avoid obligatory subsequent conditions that could be very hard to write in complicated grammars. I totally understand how does this grammar from my example work. It works correctly. I just want to tweak it in such a manner that discovering an 'ID' would mean that this optional mysubrule is actually present and its failure would definitely indicate a mistake in the text being parsed.

In reply to Re^2: Parse::Recdescent optional subrule commit by campugnatus
in thread Parse::Recdescent optional subrule commit by campugnatus

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