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

Justin Murray jmurray at aerotech.com
Fri Feb 11 10:33:25 PST 2011


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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