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Re: [HACKERS] Updated TODO item

From: Thomas Lockhart <lockhart(at)fourpalms(dot)org>
To: Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>
Cc: Gavin Sherry <swm(at)linuxworld(dot)com(dot)au>, Kaare Rasmussen <kar(at)kakidata(dot)dk>, pgsql-patches(at)postgresql(dot)org
Subject: Re: [HACKERS] Updated TODO item
Date: 2002-01-08 04:03:42
Message-ID: 3C3A6F9E.3DE49B19@fourpalms.org (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
> I might be thicker than a whale sandwich (10 points if you can pick the
> quote :) ), but can someone please tell me what a shift/reduce issue is,
> exactly...

It is what you will come to know and love if you get involved with
grammars written in yacc. yacc (and some related parsers) look ahead one
token to decide what parsing path to take. So if it takes more than one
token to figure that out, you will get a shift/reduce or reduce/reduce
error, and the parser will end up chosing *one* of the possibilities
every time.

You can make these errors go away by restructuring the language or by
restructuring the grammar specification to allow multiple "threads" of
parsing to be carried forward until possible conflicts are resolved. We
use every and all technique to shoehorn SQL and extensions into a
yacc/bison tool ;)

                  - Thomas

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