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Re: memscan() function or equivalent

From Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups comp.lang.c
Subject Re: memscan() function or equivalent
Date 2017-06-10 13:17 +0100
Organization A noiseless patient Spider
Message-ID <87tw3o9gve.fsf@bsb.me.uk> (permalink)
References (2 earlier) <12fb0e96-0ac3-442d-8d04-baaef4234a85@googlegroups.com> <20170607164800.a6fba9d07170ec5d056d25a0@gmail.com> <878tl3g5jw.fsf@bsb.me.uk> <kfnmv9h9d47.fsf@x-alumni2.alumni.caltech.edu> <878tl0fjh1.fsf@gmail.com>

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Gareth Owen <gwowen@gmail.com> writes:

> Tim Rentsch <txr@alumni.caltech.edu> writes:
>
>> Many years ago I took a course from Alan Perlis, who was at that
>> time a fan of APL (and also other things, I don't mean APL only).
>> Describing APL, a phrase he used that stuck in my mind is "all in
>> one fell swoop", talking about computation that is done using
>> array operations rather than looping.  At first I didn't see what
>> he was getting at, but over time I started to see the value of
>> computing based on data rather than computing based on control
>> flow.  My preference here for 'k += *s0 == c0;' is mainly an
>> outgrowth of that insight.
>
> I totally understand and respect this opinion -- and I definitely don't
> feel desperately strongly -- but offer the following rejoinder, courtesy
> of Don Knuth
>
>    "Let us change our traditional attitude to the construction of
>     programs: Instead of imagining that our main task is to instruct a
>     computer what to do, let us concentrate rather on explaining to
>     human beings what we want a computer to do"
>
> k += (*s0 == c0) (and as I read it, your rationale for it) falls firmly
> in the former category.

Curious.  I have exactly the reverse view!  The 'if' form is the one
that painstakingly explains what the machine should do.  To find out
what it calculates you have to (mentally) unwind the actions into a
computation.

The *s0 == c0 is an indicator function (APL uses these a lot) giving
zero for the 'no' cases and one for the 'yes' cases.  A count of things
(any things) in a sequence is the sum of an suitable indicator function
mapped onto the elements of the sequence.  Ideally, I'd prefer not to
have a walking pointer because that, again, is too much "how" and not
enough "what" for me.

Now obviously which way the balance falls has a lot to do with who you
expect to be reading the code, but for many people summing a 0/1
function over a list is almost the definition of counting.  For others,
the clearest explanation is "is this one of the ones we want? yes? OK
add one to the counter" but that's way too much "how" for me.

-- 
Ben.

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memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 06:16 -0700
  Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 15:47 +0200
    Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 07:15 -0700
      Re: memscan() function or equivalent scott@slp53.sl.home (Scott Lurndal) - 2017-06-07 14:34 +0000
        Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 07:42 -0700
          Re: memscan() function or equivalent scott@slp53.sl.home (Scott Lurndal) - 2017-06-07 14:45 +0000
            Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 08:07 -0700
              Re: memscan() function or equivalent jameskuyper@verizon.net - 2017-06-07 09:14 -0700
                Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 09:33 -0700
      Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 16:48 +0200
        Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 08:31 -0700
          Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 17:37 +0200
            Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 08:47 -0700
              Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 18:02 +0200
                Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 09:09 -0700
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 18:34 +0200
                Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 09:54 -0700
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 19:01 +0200
                Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 10:17 -0700
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 19:53 +0200
                Re: memscan() function or equivalent asetofsymbols@gmail.com - 2017-06-07 22:15 -0700
                Re: memscan() function or equivalent asetofsymbols@gmail.com - 2017-06-07 22:26 -0700
                Re: memscan() function or equivalent asetofsymbols@gmail.com - 2017-06-07 22:56 -0700
                Re: memscan() function or equivalent asetofsymbols@gmail.com - 2017-06-07 23:03 -0700
            Re: memscan() function or equivalent scott@slp53.sl.home (Scott Lurndal) - 2017-06-07 16:10 +0000
              Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 09:30 -0700
        Re: memscan() function or equivalent Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-07 16:50 +0100
          Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 08:58 -0700
            Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 09:03 -0700
              Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 09:07 -0700
              Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-07 17:30 +0100
                Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 09:36 -0700
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-07 17:48 +0100
                Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 09:57 -0700
                Re: memscan() function or equivalent Ike Naar <ike@iceland.freeshell.org> - 2017-06-12 05:54 +0000
                Re: memscan() function or equivalent Keith Thompson <kst-u@mib.org> - 2017-06-07 09:48 -0700
                Re: memscan() function or equivalent Gareth Owen <gwowen@gmail.com> - 2017-06-07 20:55 +0100
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-07 22:13 +0100
                Re: memscan() function or equivalent Keith Thompson <kst-u@mib.org> - 2017-06-07 16:02 -0700
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-08 01:26 +0100
                Re: memscan() function or equivalent Ian Collins <ian-news@hotmail.com> - 2017-06-08 13:00 +1200
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-08 09:48 +0100
                Re: memscan() function or equivalent "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-10 08:52 +0200
            Re: memscan() function or equivalent supercat@casperkitty.com - 2017-06-07 10:00 -0700
              Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 10:13 -0700
                Re: memscan() function or equivalent supercat@casperkitty.com - 2017-06-07 11:19 -0700
                Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-07 11:27 -0700
            Re: memscan() function or equivalent Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-07 21:18 +0100
          Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 18:18 +0200
            Re: memscan() function or equivalent "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-07 21:15 +0200
              Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 21:16 +0200
                Re: memscan() function or equivalent "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-10 09:08 +0200
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-10 09:56 +0200
                Re: memscan() function or equivalent "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-10 17:14 +0200
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-10 17:38 +0200
                Re: memscan() function or equivalent David Kleinecke <dkleinecke@gmail.com> - 2017-06-10 11:52 -0700
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-10 20:03 +0100
                Re: memscan() function or equivalent Keith Thompson <kst-u@mib.org> - 2017-06-10 13:32 -0700
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-10 23:40 +0200
                Re: memscan() function or equivalent Anton Shepelev <anton.txt@gmail.com> - 2017-06-11 00:53 +0300
                Re: memscan() function or equivalent Anton Shepelev <anton.txt@gmail.com> - 2017-06-11 01:11 +0300
                Re: memscan() function or equivalent Ian Collins <ian-news@hotmail.com> - 2017-06-11 10:26 +1200
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-11 00:32 +0200
                Re: memscan() function or equivalent "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-11 10:05 +0200
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-11 10:06 +0200
                Re: memscan() function or equivalent Keith Thompson <kst-u@mib.org> - 2017-06-11 13:19 -0700
                Re: memscan() function or equivalent Anton Shepelev <anton.txt@gmail.com> - 2017-06-11 02:17 +0300
                Re: memscan() function or equivalent supercat@casperkitty.com - 2017-06-10 15:21 -0700
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-11 00:19 +0200
                Re: memscan() function or equivalent Anton Shepelev <anton.txt@gmail.com> - 2017-06-11 02:15 +0300
                Re: memscan() function or equivalent "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-11 10:36 +0200
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-11 10:46 +0200
                Re: memscan() function or equivalent asetofsymbols@gmail.com - 2017-06-10 22:25 -0700
                Re: memscan() function or equivalent "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-10 15:13 -0700
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-10 23:21 +0100
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-11 00:28 +0200
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-11 10:56 +0100
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-11 13:27 +0200
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-11 13:19 +0100
                Re: memscan() function or equivalent Ike Naar <ike@iceland.freeshell.org> - 2017-06-11 18:36 +0000
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-11 20:22 +0100
                Re: memscan() function or equivalent Ike Naar <ike@iceland.freeshell.org> - 2017-06-12 06:09 +0000
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-12 10:38 +0100
                Re: memscan() function or equivalent asetofsymbols@gmail.com - 2017-06-12 05:30 -0700
                Re: memscan() function or equivalent Ike Naar <ike@iceland.freeshell.org> - 2017-06-12 13:51 +0000
                Re: memscan() function or equivalent bartc <bc@freeuk.com> - 2017-06-12 15:04 +0100
                Re: memscan() function or equivalent Ike Naar <ike@iceland.freeshell.org> - 2017-06-12 21:26 +0000
                Re: memscan() function or equivalent "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-11 10:04 +0200
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-11 10:13 +0200
                Re: memscan() function or equivalent "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-11 13:38 +0200
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-11 14:18 +0200
                Re: memscan() function or equivalent supercat@casperkitty.com - 2017-06-11 09:57 -0700
                Re: memscan() function or equivalent Melzzzzz <Melzzzzz@zzzzz.com> - 2017-06-11 17:18 +0000
                Re: memscan() function or equivalent "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-11 09:53 +0200
                Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-11 10:00 +0200
                Re: memscan() function or equivalent "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-11 13:41 +0200
              Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 21:24 +0200
              Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 21:55 +0200
          Re: memscan() function or equivalent Gareth Owen <gwowen@gmail.com> - 2017-06-07 20:54 +0100
            Re: memscan() function or equivalent David Brown <david.brown@hesbynett.no> - 2017-06-07 23:00 +0200
              Re: memscan() function or equivalent Gareth Owen <gwowen@gmail.com> - 2017-06-08 08:16 +0100
                Re: memscan() function or equivalent David Brown <david.brown@hesbynett.no> - 2017-06-08 10:55 +0200
                Re: memscan() function or equivalent Gareth Owen <gwowen@gmail.com> - 2017-06-08 11:44 +0100
                Re: memscan() function or equivalent David Brown <david.brown@hesbynett.no> - 2017-06-08 13:11 +0200
                Re: memscan() function or equivalent Gareth Owen <gwowen@gmail.com> - 2017-06-08 13:45 +0100
                Re: memscan() function or equivalent David Brown <david.brown@hesbynett.no> - 2017-06-08 14:51 +0200
                Re: memscan() function or equivalent supercat@casperkitty.com - 2017-06-08 08:00 -0700
          Re: memscan() function or equivalent Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-09 12:26 -0700
            Re: memscan() function or equivalent Gareth Owen <gwowen@gmail.com> - 2017-06-10 07:24 +0100
              Re: memscan() function or equivalent Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-10 13:17 +0100
                Re: memscan() function or equivalent Gareth Owen <gwowen@gmail.com> - 2017-06-10 17:18 +0100
                Re: memscan() function or equivalent Ike Naar <ike@iceland.freeshell.org> - 2017-06-11 18:11 +0000
              Re: memscan() function or equivalent Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-11 15:08 -0700
                Re: memscan() function or equivalent Gareth Owen <gwowen@gmail.com> - 2017-06-12 18:34 +0100
                Re: memscan() function or equivalent Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-14 09:52 -0700
                Re: memscan() function or equivalent Gareth Owen <gwowen@gmail.com> - 2017-06-14 19:56 +0100
                Re: memscan() function or equivalent Keith Thompson <kst-u@mib.org> - 2017-06-14 12:20 -0700
                Re: memscan() function or equivalent Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-17 06:37 -0700
                Re: memscan() function or equivalent supercat@casperkitty.com - 2017-06-17 10:02 -0700
      Re: memscan() function or equivalent David Brown <david.brown@hesbynett.no> - 2017-06-07 16:51 +0200
        Re: memscan() function or equivalent GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-07 17:00 +0200
          Re: memscan() function or equivalent supercat@casperkitty.com - 2017-06-07 08:53 -0700

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