All,
I remember reading that in relatively recent versions of Perl, a recursive function called by sort would result in a segfault. I don't know the particulars and may not even be remembering correctly. I decided to try my luck here and was happily suprised to find out that not only did it not segfault - it actually worked*.

I then decided to try and convert the code to use the goto &sub form to see if it made any difference in performance. See Pure Perl tail call optimization for more information. 

#!/usr/bin/perl
use strict;
use warnings;

my @data = map {chomp; [ split '/' ] } <DATA>;
@data = map { join '/', @$_ } sort my_sort @data;
print $_,$/ for @data;

sub my_sort {
    my $i = $_[0] || 0;

    if ( defined $a->[$i] && defined $b->[$i] ) {
        if ( my $result = $a->[$i] <=> $b->[$i] ) {
            return $result;
        }        
        ++$_[0];
        goto &my_sort;
    }
    return defined $a->[$i] ? 1 : -1;
}

__DATA__
0/1/2/3
0
0/4/5/6
0/4
0/1
0/1/2
0/4/5
0/10/111/145
0/10/111
0/10

[download]
This b0rk on my box (perl -V output available upon request). I confirmed that the function worked correctly when not called as a parameter to sort. After "playing" around, I discovered the following change made it start working again. 
#@data = map { join '/', @$_ } sort my_sort @data;
@data = map { join '/', @$_ } sort { my_sort() } @data;

[download]
Can anyone shed any light on what is going on here? This is purely for my own education and does not reflect what I would be doing in production code.

Cheers - L~R

* - It works when the data does not contain duplicates

Update: In a nutshell, autovivication of @_ with goto &sub is broke when using the sort SUBNAME LIST prototype but not the sort BLOCK LIST prototype. I still have no idea why though!

In reply to Sorting, recursion, and tail-call optimizations by Limbic~Region

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