Re: Precedence Misunderstanding

From	Ben Pfaff <blp@cs.stanford.edu>
Newsgroups	comp.lang.c
Subject	Re: Precedence Misunderstanding
Date	2012-07-18 10:03 -0700
Message-ID	<87y5mhgfxb.fsf@blp.benpfaff.org> (permalink)
References	<ju2p36$qj9$1@dont-email.me> <874np7j8br.fsf@blp.benpfaff.org> <ju4knh$4f4$1@speranza.aioe.org> <878veihylm.fsf@blp.benpfaff.org> <ju6l4f$gvf$1@speranza.aioe.org>

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Rui Maciel <rui.maciel@gmail.com> writes:

> Ben Pfaff wrote:
>
>> Can you expand on that?  It sounds like you are referring to
>> linear algebra or other mathematical concepts, but I do not know
>> how they apply in this situation.
>
> Consider floating point operations.  When a floating-point exception is 
> raised, the corresponding floating-point status flag is set.  This is 
> described as a "side-effect" of exceptional floating-point operations.  
>
> So, although conceptually we may perceive these operators as mapping a set 
> of floating-point values to a floating-point value, they actually map a set 
> of floating-point values to a tuple formed by a floating-point value and a 
> fenv_t state.  More specifically, instead of performing a map similar to:
>
> {float x, float y} -> operator(x,y) \in {float}
>
> ...these operators actually are similar to:
>
> {float x, float y} -> operator(x,y) \in {float, fenv_t}
>
> So, in this example, just because, conceptually, we tend to ignore the 
> fenv_t type, it doesn't mean it doesn't exist or that it isn't a part of 
> these operators' co-domain.  It does, and although it tends to be swept 
> under the proverbial rug, it is very much an integral part of the definition 
> of these floating-point operators.  
>
> The same also happens with elements which are a part of an operator's domain 
> but are ignored by a programmer.  If the outcome of an operator depends on 
> some state then the state that influences this outcome, along with any flag 
> that might be set in the process, are naturally a part of these operators' 
> domain and co-domain.  Not being aware of these elements or how they 
> influence the outcome of a computation doesn't mean that there is a hole in 
> basic algebra or in lambda calculus.

I didn't say that there was a hole in basic algebra or lambda
calculus.  I said that "we aren't taught about [side effects] in
our math classes" and "That's because side effects don't exist in
math."  I stand by those remarks: in the years of math classes
that I took, side effects never came up.  If I had spoken up in a
math class, saying "But what about side effects?", no one would
have understood what I was talking about.

Math textbooks don't tell you that you have to evaluate the
terminals from left to right, or in any other order, since the
order of evaluation just doesn't matter without introducing side
effects.

Thread

Precedence Misunderstanding Charles Richmond <frizzle@aquaporin4.com> - 2012-07-16 23:18 -0500
  Re: Precedence Misunderstanding Ben Pfaff <blp@cs.stanford.edu> - 2012-07-16 21:54 -0700
    Re: Precedence Misunderstanding Ben Pfaff <blp@cs.stanford.edu> - 2012-07-16 22:13 -0700
      Re: Precedence Misunderstanding Ben Pfaff <blp@cs.stanford.edu> - 2012-07-16 22:36 -0700
        Re: Precedence Misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-07-17 13:57 +0100
    Re: Precedence Misunderstanding "Charles Richmond" <numerist@aquaporin4.com> - 2012-07-17 13:35 -0500
      Re: Precedence Misunderstanding "io_x" <a@b.c.invalid> - 2012-07-17 20:48 +0200
      Re: Precedence Misunderstanding Robert Wessel <robertwessel2@yahoo.com> - 2012-07-17 13:45 -0500
      Re: Precedence Misunderstanding Ben Pfaff <blp@cs.stanford.edu> - 2012-07-17 12:27 -0700
        Re: Precedence Misunderstanding Willem <willem@toad.stack.nl> - 2012-07-17 20:20 +0000
      Re: Precedence Misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-07-17 20:34 +0100
        Re: Precedence Misunderstanding Ben Pfaff <blp@cs.stanford.edu> - 2012-07-17 12:39 -0700
          Re: Precedence Misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-07-17 20:57 +0100
        Re: Precedence Misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-07-17 20:48 +0100
          Re: Precedence Misunderstanding Philip Lantz <prl@canterey.us> - 2012-07-17 21:12 -0700
            Re: Precedence Misunderstanding Ike Naar <ike@iceland.freeshell.org> - 2012-07-18 07:14 +0000
              Re: Precedence Misunderstanding "BartC" <bc@freeuk.com> - 2012-07-18 10:11 +0100
                Re: Precedence Misunderstanding Ben Pfaff <blp@cs.stanford.edu> - 2012-07-18 09:18 -0700
                Re: Precedence Misunderstanding Rui Maciel <rui.maciel@gmail.com> - 2012-07-18 18:10 +0100
                Re: Precedence Misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-07-18 18:27 +0100
                Re: Precedence Misunderstanding Rui Maciel <rui.maciel@gmail.com> - 2012-07-18 18:53 +0100
                Re: Precedence Misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-07-18 21:07 +0100
                Re: Precedence Misunderstanding Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-07-19 20:47 +0300
              Re: Precedence Misunderstanding Philip Lantz <prl@canterey.us> - 2012-07-18 23:54 -0700
                Re: Precedence Misunderstanding Ike Naar <ike@sverige.freeshell.org> - 2012-07-19 07:21 +0000
      Re: Precedence Misunderstanding "BartC" <bc@freeuk.com> - 2012-07-17 20:42 +0100
      Re: Precedence Misunderstanding Willem <willem@toad.stack.nl> - 2012-07-17 20:38 +0000
        Re: Precedence Misunderstanding Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-07-19 20:54 +0300
          Re: Precedence Misunderstanding Willem <willem@toad.stack.nl> - 2012-07-19 22:02 +0000
      Re: Precedence Misunderstanding pete <pfiland@mindspring.com> - 2012-07-17 22:31 -0400
      Re: Precedence Misunderstanding Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-07-18 00:35 -0700
    Re: Precedence Misunderstanding Rui Maciel <rui.maciel@gmail.com> - 2012-07-17 22:16 +0100
      Re: Precedence Misunderstanding Ben Pfaff <blp@cs.stanford.edu> - 2012-07-17 14:22 -0700
        Re: Precedence Misunderstanding Rui Maciel <rui.maciel@gmail.com> - 2012-07-18 16:35 +0100
          Re: Precedence Misunderstanding Ben Pfaff <blp@cs.stanford.edu> - 2012-07-18 10:03 -0700
            Re: Precedence Misunderstanding Rui Maciel <rui.maciel@gmail.com> - 2012-07-18 18:32 +0100
              Re: Precedence Misunderstanding Ben Pfaff <blp@cs.stanford.edu> - 2012-07-18 10:45 -0700
                Re: Precedence Misunderstanding Rui Maciel <rui.maciel@gmail.com> - 2012-07-18 19:29 +0100
                Re: Precedence Misunderstanding Ben Pfaff <blp@cs.stanford.edu> - 2012-07-18 11:45 -0700
                Re: Precedence Misunderstanding Keith Thompson <kst-u@mib.org> - 2012-07-18 13:26 -0700
                Re: Precedence Misunderstanding Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-07-19 00:51 -0700
              Re: Precedence Misunderstanding Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-07-19 00:11 -0700
  Re: Precedence Misunderstanding Robert Wessel <robertwessel2@yahoo.com> - 2012-07-17 00:05 -0500
  Re: Precedence Misunderstanding Ike Naar <ike@iceland.freeshell.org> - 2012-07-17 07:40 +0000

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