[antlr-interest] Re: ANTLR and guarded predicates

lgcraymer lgc at mail1.jpl.nasa.gov
Wed Mar 20 11:02:38 PST 2002

--- In antlr-interest at y..., mzukowski at b... wrote:
> I don't have time to look into why it's not working right now, but 
you could
> certainly get by with a subrule:
> production: (syntax guard)=>({semantic test}? another_production)
>           | some_other_production
>           ;
> Also note that PCCTS properly hoisted predicates into calling rules. 
> does not, you will have to manually hoist the rule yourself, like I 
did with
> the typedef rule in the GCC grammar.
> Monty

ANTLR attaches sempreds to subrules (explicit or implied) internally, 
so Monty's solution should work properly.  Fixing the internals 
without breaking something else might be difficult:  as Ric has 
mentioned in other emails, ANTLR's internal "tree" (custom, 
unfortunately, not AST-based) structure is messy to deal with and 
needs a redesign/rewrite.



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