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Re: Unexpected reduce/reduce conflicts

Re: Unexpected reduce/reduce conflicts by José Valim
- Re: Unexpected reduce/reduce conflicts by José Valim

Re: Unexpected reduce/reduce conflicts

From:: José Valim
Date:: 2011-08-07 @ 12:22

Hello!

I am having unexpected reduce/reduce conflicts.
I have tried it in yecc (Erlang's version of yacc) and it yields no
conflicts.
Could someone please help me understand what is going on here and how to
solve it?

Here is the grammar:

    expressions : stat EOF ;

    stat : NAME '=' exp | functioncall;

    exp : NULL | prefixexp;

    prefixexp : var | functioncall | '(' exp ')';

    functioncall : prefixexp '(' exp ')';

The reduce conflict is this:

    stat -> functioncall . #lookaheads= EOF (
    prefixexp -> functioncall . #lookaheads= EOF (

I have also put this stuff in a gist, in case someone wants to read it
there: https://gist.github.com/f22bae54839fe93bf297

As far as I know, the grammar above does not allow "stat (", so we shouldn't
have an issue with "(" lookahead. Also "prefixexp EOF" is only allowed after
the token "=", so in theory, we shouldn't have any conflict.

Btw, thanks for the great tool. It certainly pushes the JS community
forward!

# José Valim

Re: Unexpected reduce/reduce conflicts

From:: José Valim
Date:: 2011-08-07 @ 17:31

FWIW, I have opened an issue in Jison's issues tracker that may be a
possible solution to this problem:

https://github.com/zaach/jison/issues/56

On Sun, Aug 7, 2011 at 2:10 PM, José Valim <jose.valim@gmail.com> wrote:

> Hello!
>
> I am having unexpected reduce/reduce conflicts.
> I have tried it in yecc (Erlang's version of yacc) and it yields no
> conflicts.
> Could someone please help me understand what is going on here and how to
> solve it?
>
> Here is the grammar:
>
>     expressions : stat EOF ;
>
>     stat : NAME '=' exp | functioncall;
>
>     exp : NULL | prefixexp;
>
>     prefixexp : var | functioncall | '(' exp ')';
>
>     functioncall : prefixexp '(' exp ')';
>
> The reduce conflict is this:
>
>     stat -> functioncall . #lookaheads= EOF (
>     prefixexp -> functioncall . #lookaheads= EOF (
>
> I have also put this stuff in a gist, in case someone wants to read it
> there: https://gist.github.com/f22bae54839fe93bf297
>
> As far as I know, the grammar above does not allow "stat (", so we
> shouldn't have an issue with "(" lookahead. Also "prefixexp EOF" is only
> allowed after the token "=", so in theory, we shouldn't have any conflict.
>
> Btw, thanks for the great tool. It certainly pushes the JS community
> forward!
>
> # José Valim
>