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Re: POSIX and reduce/reduce conflicts
From: |
Paul Eggert |
Subject: |
Re: POSIX and reduce/reduce conflicts |
Date: |
Tue, 9 Apr 2002 17:50:03 -0700 (PDT) |
> From: Akim Demaille <address@hidden>
> Date: 09 Apr 2002 10:35:46 +0200
>
> Bison, in case of a reduce/reduce conflict _always_ picks up the first
> rule, no matter what precedence the rules have. The idea was once
> raised to use precedence to help in case of conflicts. Does POSIX
> allow this?
No. It says that parsing conflicts are resolved as follows:
* Each rule has a precedence and associativity, given by the precedence
and associativity of the last token or literal in the rule body, overridden
by %prec.
* If there is a shift/reduce conflict, and both the grammar rule and
input symbol have precedence and associativity, resolve the conflict
in favor of the action that has the higher precedence; or if they
have the same precedence, use associativity.
* If there is a shift/reduce conflict that cannot be resolved by
precedence or associativity, do a shift, but report the conflict.
* If there is a reduce/reduce conflict, reduce by the first grammar rule,
but report the conflict.
So POSIX does not allow precedence or associativity to count for
reduce/reduce conflicts.
> But if some day Bison supports other paradigms, such as back
> tracking, then precedence can be seen as a means to order the
> search, which can be good.
Yes, but I would wait for those other paradigms before worrying about
this.
> I realize it is not clear to me whether this (using precedence in
> RR conflicts) is a feature, or a misfeature.
Given the current paradigm, I'd call it a misfeature.
- Re: User Token Numbers, (continued)
- Re: User Token Numbers, Akim Demaille, 2002/04/09
- Re: User Token Numbers, Paul Eggert, 2002/04/09
- Re: User Token Numbers, Akim Demaille, 2002/04/10
- Re: User Token Numbers, Hans Aberg, 2002/04/10
- Re: User Token Numbers, Paul Eggert, 2002/04/10
Re: User Token Numbers, Florian Krohm, 2002/04/08
Re: POSIX and reduce/reduce conflicts, Paul Eggert, 2002/04/08
Re: POSIX and reduce/reduce conflicts, Hans Aberg, 2002/04/09