From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Chris Bitmead <chrisb(at)nimrod(dot)itg(dot)telstra(dot)com(dot)au> |
Cc: | Chris Bitmead <chris(at)bitmead(dot)com>, Postgres Hackers List <hackers(at)postgresql(dot)org> |
Subject: | Re: Re: gram.y PROBLEM with UNDER |
Date: | 2000-05-26 02:09:17 |
Message-ID: | 1800.959306957@sss.pgh.pa.us |
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Chris Bitmead <chrisb(at)nimrod(dot)itg(dot)telstra(dot)com(dot)au> writes:
>> If you don't get rid of those then your parser will behave in surprising
>> ways. So far you have noticed the fallout from only one of those
>> conflicts, but every one of them is a potential bug. Be advised that
>> gram.y patches that create unresolved conflicts will *not* be accepted.
> I thought shift/reduce conflicts were part and parcel of most language
> syntaxes. reduce/reduce being rather more naughty. The standard syntax
> already produces 95 shift/reduce conflicts. Can you clarify about
> unresolved conflicts not being accepted?
What's to clarify? The existing grammar does produce a long list of
*resolved* conflicts, which are not very interesting (they just indicate
that we are using operator precedence rules instead of creating a
detailed grammar for expressions). Unresolved conflicts are a far
more serious problem, because they tell you that there is an unreachable
part of your language. As indeed was happening to you in this case.
regards, tom lane
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