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From: Andrew.Vignaux@comp.vuw.ac.nz (Andrew Vignaux)
Newsgroups: comp.lang.perl
Subject: Re: sort
Message-ID: <1990Sep01.001741.17511@comp.vuw.ac.nz>
Date: 1 Sep 90 00:17:41 GMT
References: <1990Aug21.224327.20194@iwarp.intel.com> <1990Aug22.111018.3329@comp.vuw.ac.nz> <MIKE.MCMANUS.90Aug28165252@mustang.FtCollins.NCR.com> <105536@convex.convex.com> <1990Aug29.191454.23527@iwarp.intel.com> <9337@jpl-devvax.JPL.NASA.GOV>
Sender: news@comp.vuw.ac.nz (News Admin)
Organization: Comp Sci, Victoria University, Wellington, New Zealand.
Lines: 55

In article <1990Aug29.191454.23527@iwarp.intel.com>
merlyn@iwarp.intel.com (Randal Schwartz) writes:
: In article <105536@convex.convex.com>, tchrist@convex (Tom
Christiansen) writes:
: | Is this simple enough for the sort function?
: | 
: |     sub bynum { substr($a,$[+1,10) > substr($b,$[+1,10); }
: 
: Nope nope nope.  I made that same mistake once.  Think about
: what this returns... either "1" or "0", not "1" or "-1".  Arrrgh. :-)

Actually, the Berkeley qsort (well let's be precise -- the qsort on
our MORE/bsd 4.3+ boxes running on hp300s) still manages to sort if
you use this comparison routine!

In article <9337@jpl-devvax.JPL.NASA.GOV>, lwall@jpl-devvax.JPL.NASA.GOV
(Larry Wall) writes:
> I just had the weirdest thought.  The ne and != operators should maybe
> return -1 or +1 when the operands aren't equal.
> 
> Larry

This is a great idea!  In conjunction with || returning the last value
evaluated means sort functions can turn into:

    sub sort_it { $key1{$a} ne $key1{$b} || -(&fun2{$a} != &fun2{$b}); }

where &fun2() can return floats!

Unfortunately, it will break some of my scripts.  E.g

    if (($sort_rank != 0) + ($sort_articles != 0) + ($sort_size != 0) > 1) {
	print STDERR "$program: only one of -r, -a, -s should be supplied\n";
	exit (1);
    }

where $sort_* could be -1, 0, +1.  But I can fix those.

Possible problems:
    +	it looks strange.  Take another look at sort_it!  Does it sort
          things the right way?

    +	people will have to re-think how to use comparison operators
          because "!=" does not mean "!( == )" E.g negating an
          expression (ala De Morgan) will take some thought

    +	-(a != b)  <=>  (-a != -b)  which is new!

    +	it'll screw up my C programming :-)

I realise it isn't a democracy, but you've got my vote.

Andrew
-- 
Domain address: Andrew.Vignaux@comp.vuw.ac.nz