| From: | Andrew Dunstan <andrew(at)dunslane(dot)net> |
|---|---|
| To: | "Florian G(dot) Pflug" <fgp(at)phlo(dot)org> |
| Cc: | Zoltan Boszormenyi <zb(at)cybertec(dot)at>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <bruce(at)momjian(dot)us>, PG Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Re: IDENTITY/GENERATED v36 Re: [PATCHES] Final version of IDENTITY/GENERATED patch |
| Date: | 2007-04-16 18:47:55 |
| Message-ID: | 4623C4DB.1070505@dunslane.net |
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| Lists: | pgsql-hackers pgsql-patches |
Florian G. Pflug wrote:
>>>>
>>>> bison -y -d gram.y
>>>> conflicts: 2 shift/reduce
>
> I'ts been quite a time since I last used bison, but as far as I
> remember, you can tell it to write a rather details log about
> it's analysis of the grammar. That log should include more
> detailed information about those conflicts - maybe that helps
> to figure out their exact cause, and to find a workaround.
>
You can almost always get rid of shift/reduce conflicts by unwinding
some of the productions - resist the temptation to factor the grammar.
The effect of this is to eliminate places where the parser has to decide
between shifting and reducing. (This is why, for example, almost all the
"drop foo if exists" variants require separate productions rather than
using opt_if_exists.)
cheers
andrew
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