[antlr-interest] problem with semantic predicates, local declarations, and hoisting

[Thomas Brandon]

On 8/9/07, Madden, Warren <warren.madden at lmco.com> wrote:
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> Greetings!
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> I'm trying to write a grammar that recognizes a particular data format that
> includes some fixed length and some variable length fields.  I'm running
> into problems with my semantic predicates being hoisted up, and moving out
> of the context of my local variables.  Hoping someone can point me in the
> right direction to solve my problem.
>
This is a known bug\issue (not sure which, i.e. whether it will be
fixed). Use a field as you suggest, or (probably cleaner) a dynamic
scope instead. Something like:
> mandatory_child
scope {
    int n;
}
@init { mandatory_child::n = 0; }
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>             :           ( { mandatory_child::n <= 17 }?=>
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>                         ~(CR|LF)
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>                         { mandatory_child::n++; })+
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>                         {System.out.println("text is " + $text + ", n is " +
> mandatory_child::n );}
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>                         {mandatory_child::n == 12 || mandatory_child::n == 18}?;
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> It appears that ANTLR is taking my predicate and moving it into a DFA, but
> not carrying the declaration of n along with it.  Any ideas how I can fix
> this?  Should I make n a class variable using @members, rather than using
> @init as shown in the example?
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> Thanks!
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> Warren Madden