Re: this should work

From	Rainer Weikusat <rweikusat@mssgmbh.com>
Newsgroups	comp.lang.perl.misc
Subject	Re: this should work
Date	2013-07-15 15:05 +0100
Message-ID	<87ehazhqap.fsf@sapphire.mobileactivedefense.com> (permalink)
References	<krkm21$19jd$1@news.ntua.gr> <87txk0oioo.fsf@sapphire.mobileactivedefense.com> <spt3ba-i9r2.ln1@anubis.morrow.me.uk> <87ip0cgfli.fsf@sapphire.mobileactivedefense.com> <kp8dba-9591.ln1@anubis.morrow.me.uk>

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Ben Morrow <ben@morrow.me.uk> writes:
> Quoth Rainer Weikusat <rweikusat@mssgmbh.com>:
>> Ben Morrow <ben@morrow.me.uk> writes:
>> > A variable is just a way of giving a value a name;
>> 
>> This is true for so-called 'functional programming languages' but Perl
>> isn't one: There, a 'variable' is something like a deposit box
>> (term?): A container which can be used to store 'stuff' of a certain
>> kind (depending on the type of box) until it is again needed which can
>> be 'addressed' in a convenient way (usually, by using an abstract name
>> referring to the 'function' of this variable).
>
> How is that different from 'just a way of giving a value a name'?

In simply terms, it is 'stuff the value into the named box' vs
'evaluating a term in the context of some binding', that is, with
certain set of 'name substitution rules' in place. I don't know if
something like 'introductory text books' (or WWW texts) on
'functional programming' (vs 'programming with imperative languages')
exist but if they do, you'd find a better explanation there
(especially one you're more likely to consider than to reject it 'with
a jerk of your knee' because it comes with $authority attached :->).

>> > The whole point of lexical variables is to avoid the problems that
>> > occur when uncontrolled and implicit data leakage occurs between
>> > different parts of the program; having Perl ensure that values we no
>> > longer need are properly disposed of as soon as possible is just
>> > common sense.
>> >
>> > (And, again, this is not about efficiency, either of CPU or memory. It's
>> > about making the code comprehensible.)
>> 
>> IMO, it is about making the code incomprehensible for the sake of
>> 'efficiency', namely, to avoid the dreaded, mythological function call
>> overhead, by cramming as many different algorithms into a single run
>> of sequential code as seems remotely feasible instead of giving
>> 'different things different names' and invoke them using these in
>> higher-level control routines. If 'possible information leakage'
>> becomes a problem, the constituent parts of 'the code' are way too
>> large and do way too many different things.
>
> We were discussing these two forms:
>
>     for (...) {                         my $tmp;
>         my $tmp = "/.../$_";            for (...) {;
>         ...;                                $tmp = "/.../$_";
>     }                                       ...;
>                                         }
>
> and you claimed the second was superior on grounds of efficiency.

I didn't claim that, I pointed it out. Arguably for tactical reasons
because trying to convince people who dumped $native_language with a
sigh of relief at the earliest possible opportunity during their
educational career in order to dedicate themselves to the domain of
incomprehensible strings of non-alphabetic symbols meticiously
arranged according to some set of traditional rules that they're still
writing texts and the same rules for "don't make a mess of it" apply
as to any other text (eg, don't constantly and gratuitiously introduce
new stuff just because you can) is hopeless: Pointing out that the
result is lacking according to some measurable 'hard' criterion will
usually at least lead to the admission that "well, it does, but -
cunningly - we programmmed the computer to work around that already".

But that doesn't really belong into a discussion of problems which might
occur in large, sequential runs of code when band aids of this kind
weren't available

>> >> Do you think it was programmed to work around that because this is
>> >> such a great idea? I don't. Especially since the computer can only
>> >> work around the execution time penalty of this convention and not
>> >> against the mess in the source code ("which of the 1,375 $i I
>> >> encountered in the last 2000 lines of code is it this time?").
>> >
>> > Um, it's the one in the 'my' statement just above your cursor. That's
>> > the whole point of tight scoping: except for the various kinds of
>> > globals, which should not be created lightly and do require planning,
>> > the scope of a single variable should not exceed one screenful of
>> > code.
>> 
>> Except if 'screenful' is supposed to refer to 80x25,
>
> Of course.
>
>> it should
>> usually be less: Some random 'screenful of code' I just looked at (148
>> lines of text) contained five different complete subroutines whose
>> bodies where (from top to bottome), 5 lines of text, 12 lines of text,
>> 17 lines of text, 4 lines of text and 1 line of text.
>
> Do you understand the meaning of 'should not exceed'?

I think 'should not exceed' and 'should usually be a lot less than'
are substantially different.

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this should work "George Mpouras" <nospam.gravitalsun.antispam@spamno.hotmail.anispam.com.nospam> - 2013-07-11 01:08 +0300
  Re: this should work Jim Gibson <jimsgibson@gmail.com> - 2013-07-10 15:49 -0700
    Re: this should work George Mpouras <nospam.gravitalsun.noadsplease@hotmail.noads.com> - 2013-07-11 09:42 +0300
      Re: this should work tmcd@panix.com (Tim McDaniel) - 2013-07-11 08:02 +0000
        Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 12:45 +0100
          Re: this should work George Mpouras <nospam.gravitalsun.noadsplease@hotmail.noads.com> - 2013-07-11 15:03 +0300
            Re: this should work "Peter J. Holzer" <hjp-usenet3@hjp.at> - 2013-07-11 14:52 +0200
              Re: this should work George Mpouras <nospam.gravitalsun.noadsplease@hotmail.noads.com> - 2013-07-11 16:01 +0300
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 14:29 +0100
        Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 14:27 +0100
          Re: this should work Peter Makholm <peter@makholm.net> - 2013-07-11 15:50 +0200
      Re: this should work Jürgen Exner <jurgenex@hotmail.com> - 2013-07-11 03:34 -0700
        Re: this should work George Mpouras <nospam.gravitalsun.noadsplease@hotmail.noads.com> - 2013-07-11 13:55 +0300
          Re: this should work Peter Makholm <peter@makholm.net> - 2013-07-11 13:57 +0200
          Re: this should work Shmuel (Seymour J.) Metz <spamtrap@library.lspace.org.invalid> - 2013-07-11 09:10 -0400
            Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 21:35 +0100
    Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 10:32 +0100
      Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 12:51 +0100
        Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 13:42 +0100
          Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 16:23 +0100
            Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 17:17 +0100
              Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 18:08 +0100
              Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 21:48 +0100
          Re: this should work Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2013-07-11 10:32 -0700
            Re: this should work Jürgen Exner <jurgenex@hotmail.com> - 2013-07-11 10:48 -0700
              Re: this should work "George Mpouras" <nospam.gravitalsun.antispam@spamno.hotmail.anispam.com.nospam> - 2013-07-11 21:38 +0300
              Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 23:08 +0100
            Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 18:48 +0100
              Re: this should work Charles DeRykus <derykus@gmail.com> - 2013-07-11 12:03 -0700
                Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 22:02 +0100
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 23:06 +0100
                Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-12 01:04 +0100
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-15 13:41 +0100
                Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-15 14:07 +0100
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-15 15:05 +0100
                Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-15 21:02 +0100
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-15 23:58 +0100
                Re: this should work tmcd@panix.com (Tim McDaniel) - 2013-07-15 17:23 +0000
                Re: this should work Charlton Wilbur <cwilbur@chromatico.net> - 2013-07-15 15:40 -0400
              Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 21:58 +0100
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 23:17 +0100
                [OT] scoping Ivan Shmakov <oneingray@gmail.com> - 2013-07-12 07:50 +0000
                Re: [OT] scoping aka 'new holes in old shoes' Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-12 11:53 +0100
                [OT] engineering Ivan Shmakov <oneingray@gmail.com> - 2013-07-15 11:37 +0000
                Re: [OT] engineering Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-16 21:49 +0100
                Re: [OT] engineering Ivan Shmakov <oneingray@gmail.com> - 2013-07-17 09:27 +0000
                Re: [OT] engineering Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-17 15:53 +0100
                Re: [OT] engineering Ivan Shmakov <oneingray@gmail.com> - 2013-07-22 10:36 +0000
                Re: [OT] engineering Shmuel (Seymour J.) Metz <spamtrap@library.lspace.org.invalid> - 2013-07-23 06:43 -0400
                Re: [OT] engineering Ivan Shmakov <oneingray@gmail.com> - 2013-07-22 10:38 +0000
                Re: [OT] engineering Rui Maciel <rui.maciel@gmail.com> - 2013-07-26 10:09 +0100
                Re: [OT] scoping "Peter J. Holzer" <hjp-usenet3@hjp.at> - 2013-07-12 14:58 +0200
                Re: [OT] scoping Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-12 15:50 +0100
                Re: [OT] scoping Shmuel (Seymour J.) Metz <spamtrap@library.lspace.org.invalid> - 2013-07-12 13:34 -0400
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-12 22:04 +0100
                Re: [OT] scoping Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-13 13:13 +0100
                Re: [OT] scoping John Black <jblack@nospam.com> - 2013-07-13 20:01 -0500
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-14 03:24 +0100
                Re: [OT] scoping "Dr.Ruud" <rvtol+usenet@xs4all.nl> - 2013-07-14 10:49 +0200
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-14 13:13 +0100
                Re: [OT] scoping "Dr.Ruud" <rvtol+usenet@xs4all.nl> - 2013-07-14 17:02 +0200
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-14 22:21 +0100
                Re: [OT] scoping "Dr.Ruud" <rvtol+usenet@xs4all.nl> - 2013-07-15 02:21 +0200
                Re: [OT] scoping Xho Jingleheimerschmidt <xhoster@gmail.com> - 2013-07-14 17:04 -0700
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-15 14:12 +0100
                Re: [OT] scoping tmcd@panix.com (Tim McDaniel) - 2013-07-14 15:11 +0000
                Re: [OT] scoping "Dr.Ruud" <rvtol+usenet@xs4all.nl> - 2013-07-14 17:34 +0200
                Re: [OT] scoping Xho Jingleheimerschmidt <xhoster@gmail.com> - 2013-07-14 15:34 -0700
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-15 14:27 +0100
                Re: [OT] scoping John Black <jblack@nospam.com> - 2013-07-14 23:48 -0500
                Re: [OT] scoping Martijn Lievaart <m@rtij.nl.invlalid> - 2013-07-13 12:14 +0200
      Re: this should work David Harmon <source@netcom.com> - 2013-07-11 10:02 -0700
        Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 22:04 +0100
          Re: this should work David Harmon <source@netcom.com> - 2013-07-12 09:34 -0700
            Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-12 18:16 +0100
        Re: this should work "Dr.Ruud" <rvtol+usenet@xs4all.nl> - 2013-07-12 15:44 +0200
          Re: this should work David Harmon <source@netcom.com> - 2013-07-12 15:53 -0700
  Re: this should work Shmuel (Seymour J.) Metz <spamtrap@library.lspace.org.invalid> - 2013-07-11 09:14 -0400
    Re: this should work "George Mpouras" <nospam.gravitalsun.antispam@spamno.hotmail.anispam.com.nospam> - 2013-07-11 19:45 +0300

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