Re: Grammar with low-precedence postfix operator?

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From	Robert Jacobson <rljacobson@gmail.com>
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Subject	Re: Grammar with low-precedence postfix operator?
Date	Sat, 7 Feb 2015 10:30:43 -0800 (PST)
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Thanks for the response. I'll have to digest this for a bit.

On Friday, 6 February 2015 22:12:10 UTC-5, Kaz Kylheku  wrote:
> On 2015-02-05, Robert Jacobson <rljacobson@gmail.com> wrote:
> > I'm trying to write an ANTLR4 grammar for a language with a low precedence
> > postfix operator (Wolfram Language with '&', but I use a simple toy grammar
> > below). I'm struggling with finding the right pattern to express this > > language.
>
> I suspect this is not nicely solvable by LALR type tools. Only with hacks.

But if I abandon implicit multiplication, collapse the grammar to a single
rule, and let ANTLR handle operator precedence, ANTLR produces a parser that
works. (I haven't made an attempt at a yacc grammar.) Perhaps this is because
ANTLR produces ALL(*) parsers.

> If you want 2+2++^3 to mean (2+2)++^3, that means that you need
> a special low-precedence versions of ^ (and other operators) for that
> case, so the ++ expression can be a constituent of something.
>
> Try something along these lines. This Yacc grammar only gives me one
> shift-reduce conflicts, on account of the empty production rule for
> pp_factor_continue.  I didn't test it; I only skimmed through the state
> transitions in y.output:

I'll experiment with this, but this strategy strikes me as impractical for
large grammars because you'd need to duplicate a significant portion of the
grammar for the low-precedence versions of operators that can follow ++, yes?

Thread

Grammar with low-precedence postfix operator? Robert Jacobson <rljacobson@gmail.com> - 2015-02-05 13:27 -0500
  Re: Grammar with low-precedence postfix operator? Kaz Kylheku <kaz@kylheku.com> - 2015-02-05 21:10 +0000
    Re: Grammar with low-precedence postfix operator? Robert Jacobson <rljacobson@gmail.com> - 2015-02-07 10:30 -0800
  Re: Grammar with low-precedence postfix operator? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-02-07 11:27 +0000
    Re: Grammar with low-precedence postfix operator? jgk@panix.com (Joe keane) - 2015-02-10 21:03 +0000
      Re: Grammar with low-precedence postfix operator? Kaz Kylheku <kaz@kylheku.com> - 2015-02-11 02:19 +0000
  Re: Grammar with low-precedence postfix operator? Stefan Monnier <monnier@iro.umontreal.ca> - 2015-02-08 12:34 -0500
    Re: Grammar with low-precedence postfix operator? Kaz Kylheku <kaz@kylheku.com> - 2015-02-09 01:24 +0000
      Re: Grammar with low-precedence postfix operator? Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2015-02-09 08:05 +0100
  Re: Grammar with low-precedence postfix operator? Robert Jacobson <rljacobson@gmail.com> - 2015-02-21 12:55 -0800

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