Re: Problem solving shift/reduce conflict

lars@bearnip.com (Lars Duening)
7 Jan 2003 23:25:17 -0500

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Related articles
Problem solving shift/reduce conflict ashwin21_99@hotmail.com (Ashwin) (2003-01-04)
Re: Problem solving shift/reduce conflict cdodd@acm.org (Chris Dodd) (2003-01-07)
Re: Problem solving shift/reduce conflict lars@bearnip.com (2003-01-07)
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From: lars@bearnip.com (Lars Duening)
Newsgroups: comp.compilers
Date: 7 Jan 2003 23:25:17 -0500
Organization: Compilers Central
References: 03-01-011
Keywords: yacc, comment
Posted-Date: 07 Jan 2003 23:25:17 EST

Ashwin <ashwin21_99@hotmail.com> wrote:


> The following is my (simplified) grammar. The starting point is ArrayType.
>
> ArrayType: ReferenceType RankSpecifiers ;
>
> ReferenceType: ClassType | ArrayType ;
>
> ClassType: OBJECT | STRING ;
>
>
> RankSpecifiers: RankSpecifier
> | RankSpecifiers RankSpecifier
> ;
>
> RankSpecifier: LEFTBRACKET RIGHTBRACKET ;


The problem is I see it is that you implement the repetition of array
indices twice: once in the ArrayType/ReferenceType rule combination,
and a second time in RankSpecifiers. The shift/reduce conflict comes to
pass when the parser encounters a LEFTBRACKET after having parsed a
LEFTBRACKET RIGHTBRACKET: at that point the parser has to choose between
shifting and continue parsing RankSpecifiers, or reducing the text so
far as ArrayType.


One solution is to drop the ReferenceType rule altogether and write
ArrayType as


ArrayType: ClassType RankSpecifiers;
[Several other people sent in similar analyses. Thanks to all. -John]

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