Re: Implicit operator precedence

Hans Aberg <>
15 Jun 2004 01:01:22 -0400

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Re: Implicit operator precedence (Hans Aberg) (2004-06-15)
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From: Hans Aberg <>
Newsgroups: comp.compilers
Date: 15 Jun 2004 01:01:22 -0400
Organization: Compilers Central
References: 04-05-102
Keywords: parse, LALR
Posted-Date: 15 Jun 2004 01:01:22 EDT (Sam Thursfield) wrote:

>Recently i've been toying with writing a yacc-style (LALR) parser
>generator. It's got to the point where it can create a fully working
>version of the infix calculator given in the bison manual.
>When it came to implementing operator precedence, as a quick hack i
>worked out that instead of all the %left DIV MUL business, i could
>simply put the rules in order and resolve shift/reduce conflicts by
>the number of the rule.

Even though POSIX requires Yacc-like parser generators to resolve conflicts
by reducing the first rule in the grammar, it is in general something that
depends on the compiler, and not the grammar.

>... my
>question is, can anyone see any obvious problems with this setup?
>[How do you tell it that ADD and SUB have the same precedence? -John]

And shift/reduce conflicts will always be resolved as reduce, so one can't
express %right and %nonassoc that way.

    Hans Aberg

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