Re: precedences vs. hierarchy

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.compilers
Subject	Re: precedences vs. hierarchy
Date	2016-06-08 09:48 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<16-06-010@comp.compilers> (permalink)
References	<16-06-001@comp.compilers> <16-06-004@comp.compilers> <16-06-008@comp.compilers>

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Kaz Kylheku <545-066-4921@kylheku.com> writes:
>You need the concept of associativity to tell whether
>A + B + C  is  (A + B) + C  or  A + (B + C).

But if + is really associative (e.g., not FP addition), these two are
equivalent.

>In table shift-reduce parsers (Yacc, and such), associativity rules
>resolve conflicts.

Of course, you can also write the grammar in an unambiguous way, then
you don't need associativity rules to resolve the ambiguity; a
disadvantage of precedence and associativity declarations is that they
can hide more ambiguities than you intended.

- anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/

Thread

precedences vs. hierarchy Andreas Schramm <bassobajo@gmail.com> - 2016-06-06 09:08 +0200
  Re: precedences vs. hierarchy "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2016-06-06 17:08 +0200
    Re: precedences vs. hierarchy Kaz Kylheku <545-066-4921@kylheku.com> - 2016-06-07 15:35 +0000
      Re: precedences vs. hierarchy "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2016-06-07 22:53 +0200
      Re: precedences vs. hierarchy anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-06-08 09:48 +0000
  Re: precedences vs. hierarchy George Neuner <gneuner2@comcast.net> - 2016-06-06 12:35 -0400
  Re: precedences vs. hierarchy federation2005@netzero.com - 2016-06-06 14:01 -0700
    Example: The Full Syntax Of Prolog (Re: precedences vs. hierarchy) rockbrentwood@gmail.com - 2016-08-24 15:45 -0700

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