Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.compilers > #1526

Re: Grammar with low-precedence postfix operator?

From jgk@panix.com (Joe keane)
Newsgroups comp.compilers
Subject Re: Grammar with low-precedence postfix operator?
Date 2015-02-10 21:03 +0000
Organization Public Access Networks Corp.
Message-ID <15-02-024@comp.compilers> (permalink)
References <15-02-006@comp.compilers> <15-02-014@comp.compilers>

Show all headers | View raw

Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
>For your example involving ^ and ++, I think that one should use
>parentheses explicitly in most cases, e.g. (a^b)++^c or a^(b++)^c.
>You can leave away the parentheses if there is no ambiguity, as in
>your 2++^3, but that's not straightforward to express in BNF.

gcc does something like this

You can say:

	if (x & y == 0)

probable error, warn or reject

	if ((x & y) == 0)

OK

	if (x & (y == 0))

OK, if that's what you want

I don't know how it is implemented.

	if (x == 1 && y == 2)

fine IMHO

	if ((x == 1) && (y == 2))

too many parens

	if (((x >= 1) && (x <= 2)) || ((y >= 1) && (y <= 2)))

way too many parens IMHO, but shouldn't reject

The reason you don't want to reject these is that,
besides that it's style, they could come from macros.

If you color parens in macros, you could also look out for macros:

#define SUM(X, Y) (X)+(Y)

probable error

#define DOUBLE(X) (2*X)

probable error

Back to comp.compilers | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web