Re: Why are ambiguous grammars usually a bad idea? Why are languages usually defined and implemented with ambiguous grammars?

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From	gah4 <gah4@u.washington.edu>
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Subject	Re: Why are ambiguous grammars usually a bad idea? Why are languages usually defined and implemented with ambiguous grammars?
Date	Mon, 27 Dec 2021 04:18:18 -0800 (PST)
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On Sunday, December 26, 2021 at 7:19:08 PM UTC-8, Roger L Costello wrote:

> I am reading the (excellent) book "flex & bison" by John Levine. Chapter 7
> talks about conflicts in grammars: shift/reduce and reduce/reduce conflicts.

> At the end of the chapter are a few exercises/questions. I'd like to check
> with you on whether my answers to the questions are accurate and complete.

As far as I know, the main cause of ambiguous grammar in programming languages
is the nested if-then-optional-else structure.  If you require else, then it isn't ambiguous,
but people like the optional else.  That usually comes out as a shift-reduce conflict,
and parser generators know how to handle that.

Otherwise, the usual regular expression has an ambiguity which is often cured
by taking the longest of the possible matches.  It seems to me that more often
I want the shorter match, though.

But you already have the reply from John Levine ...
[See previous message, where we fixed that with "fi" in 1968. -John]

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Re: Why are ambiguous grammars usually a bad idea? Why are languages usually defined and implemented with ambiguous grammars? gah4 <gah4@u.washington.edu> - 2021-12-27 04:18 -0800
  Re: Why are ambiguous grammars usually a bad idea? Why are languages usually defined and implemented with ambiguous grammars? gah4 <gah4@u.washington.edu> - 2021-12-27 19:45 -0800
  Re: Why are ambiguous grammars usually a bad idea? Why are languages usually defined and implemented with ambiguous grammars? Christopher F Clark <christopher.f.clark@compiler-resources.com> - 2021-12-28 16:18 +0200

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