The obvious answer would be to add a method reset_count() in the block, but you would have to explicitly call it before sorting, which is prone to errors.

Another way is to put together a state and a behaviour, building an object.

But if you want to go on in a functional way, you may want to build a composition of a behaviour and a state, i.e. a closure. Here a short demonstration:

use strict;

my @list1 = qw/ box cow dog apple ant/;
my @list2 = qw/ ant apple box cow dog/;

sub make_a_profilable_sorter
{
    my $criterion = shift;
    
    return sub {
        my $counter = 0;

        my @list = @_;

        @list = sort { $counter++; $criterion->( $a, $b ) } @list; 

        return ( $counter, @list );
    }
}

my $sorter1 = make_a_profilable_sorter( sub{ $_[0] cmp $_[1] } );
my $sorter2 = make_a_profilable_sorter( sub{ $_[0] cmp $_[1] } );

my ($count, @res) = $sorter1->( @list1 );
print "I sorted /@list1/ in $count steps producing /@res/\n";

my ($count, @res) = $sorter2->( @list2 );
print "I sorted /@list2/ in $count steps producing /@res/\n";
[download]

In order to learn more about this subject (very interesting, in my opinion) you could refer to the following online resources:

• Frames as repository of local state in Structure and Interpretation of Computer Programs
• On Lisp by Paul Graham. Start at page 30 (in the free pdf file)

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