Not only is a factorial calculator not a good candidate for recursion, Perl (currently) doesn't do tail-recursion optimization, which would fix your memory leak.

I'm also trying to figure out how your two examples are similar. The first defines new anonymous subs, but the second only defines one. (The additional subs are defined because you're calling the function definer over and over.) Try the following: 

use strict;             # leak occurs whether strict is used or not
 
my $fact = build_sub();
while(1) {
  print &$fact(5), $/;
}
 
sub build_sub {
  my $factorial_sub_ref;
 
  $factorial_sub_ref = sub {
    my ($number) = @_;
    if ($number < 2) { return 1; }
    return($number * &$factorial_sub_ref($number - 1));
  };
 
   return $factorial_sub_ref;
}

[download]

Also, factorials are multiplied, not added.

------
We are the carpenters and bricklayers of the Information Age.

The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.

In reply to Re: Memory leak on definition of anonymous code? by dragonchild
in thread Memory leak on definition of anonymous code? by octothorpe

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