Re: Semantic actions in Yacc ?

frazerw@dseg.ti.com writes:
>I want to add semantic actions to a Yacc parser. The way I'd considered
>of doing this is to add actions before and after each nonterminal in
>digit : {} ZERO_TOK {}
> | {} ONE_TOK {}
> ;


I'll just leave this one example. The problem that occurs is due to the
way that Bison actually creates this rule. A seperate nonterminal is created
for the first semantic action in the rule. Now before it has read any input,
(but a digit is expected), Bison has to execute a semantic action, as it is
placed before the rule. However, either one of these is possible, and a
reduce/reduce conflict is created.


To avoid this
1) Don't put semantic actions before rules -- BEST METHOD
2) Do something like this


digit : { semantic action } digit2
digit2 : ZERO_TOK { }
| ONE_TOK { }


but of course this only works if the initial semantic action is the same.


Cheers,


Charles
---
cae@dcs.warwick.ac.uk
--

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