[antlr-interest] [SPAM] [SPAM] Re: [SPAM] [SPAM] Optional expression rule alternative

[Justin Murray]

These are called Semantic Predicates. Section 12.1 in TDAR. 
Specifically, look at page 295 of the PDF. If the predicate evaluates to 
false, the alternative is effectively switched off.

- Justin

On 2/11/2011 1:04 PM, Olivier Lefevre wrote:
> Great! Not to abuse but would you know in which section of
> "The Definitive ANTLR Reference" this mentioned? I couldn't
> find it. What is this syntax called?
>
> But in my real-world problem it was actually not a choice
> between rule1 and rule2 but a question of whether to allow
> an extra alternative in the z case without too much
> verbatim repetition, i.e. (again in pseudo-code):
>
> rule[boolean z] :
>     rule1 | rule2 | ... | rule23 | (z ? rule24 : nothing) ;
>
> That is, allow rule24 if z otherwise stop at rule23.
>
> Thanks again,
>
> -- O.L.
>
>
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