Tail recursion pattern in Perl - for some reason people say Perl doesn't have tail recursion; you just need to do a little extra work.

tail-factorial.pl

#!/usr/bin/env perl

use strict;
use warnings;
use bigrat;

my $n = shift || 100;

print "$n! = " . tail_factorial($n) . "\n";

{
  my $fac;

  sub tail_factorial {
    local @_ = @_;
    $fac = 1;
    &_tail_factorial;
    return $fac;
  }

  sub _tail_factorial {
    return if $_[0] < 2;
    $fac *= $_[0];
    $_[0]--;
    goto &_tail_factorial; # tail recursion, yo
  }
}