[taos-glug] Re: my progress report

Jonathan Bartlett wrote:
> One thing I find missing in most Scheme texts is the usefulness of being
> able to combine functions.

So (with a little help from Perlmonks as I forgot about perl's lack of 
scope for nested subs) we can do this in perl with:

use strict;

my @list1 = qw/ box cow dog apple ant/;
my @list2 = (1,2,7,4,5);

sub make_counting_comparator
{
     my $criterion = shift;
     my $counter = 0;
     return (sub {

        # you could put "return" in front of the line below
         $counter++; return $criterion->( $a, $b );

     }, sub{$counter});
}

my @sorter1 = make_counting_comparator( sub{ $_[0] cmp $_[1] } );
my @sorter2 = make_counting_comparator( sub{ $_[0] <=> $_[1] } );

my @list = sort {$sorter1[0]()} @list1;
my $count = $sorter1[1]();
print "I sorted /@list1/ in $count steps producing /@list/\n";

my @list = sort {$sorter2[0]()} @list2;
my $count = $sorter2[1]();
print "I sorted /@list2/ in $count steps producing /@list/\n";

For me, this is far clearer. It is, however, pretty much a direct 
translation.  When writing this, I had initially tried to overcomplicate 
it.  Doing a more direct translation was far easier.

I know the point of Philip's exercise is to learn Scheme, but I like to 
bend the rules a bit.  Also, languages like perl seem a bit more common 
for developing applications

This one makes a copy of the list instead of sorting the initial list: 
that's the way perl's sort works.  One could use another mechanism to 
sort in place, I suppose.

When it comes to "first class"-itude, if we consider the union of 
functions and function references in perl, is that union first-class?


--john

-- 
John McDermott
Writer, Educator, Consultant
jjm@xxxxxxxxxx          http://www.jkintl.com
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