# caching previous answers 
use Memoize;
memoize('Mfactorial');
memoize('Mfactorial2');
sub Mfactorial {
    my $num = shift;
    return 1 if $num == 0 or $num == 1;
    return $num * Mfactorial($num - 1);
}
sub Mfactorial2 {
    my $iLex = shift;
    return 1 unless $iLex > 1;
    my $result =1;
    while ($iLex > 1) {
        $result = $result * $iLex;
        $iLex--;
    }
    $result;
}

__DATA__
results:
Benchmark: timing 1000000 iterations of Closure, Global, Lexical, Memo, Memo2...
   Closure: 25 wallclock secs (26.29 usr +  0.00 sys = 26.29 CPU) @ 38037.28/s (n=1000000)
    Global: 26 wallclock secs (26.41 usr +  0.00 sys = 26.41 CPU) @ 37864.45/s (n=1000000)
   Lexical: 28 wallclock secs (25.32 usr +  0.05 sys = 25.37 CPU) @ 39416.63/s (n=1000000)
      Memo: 16 wallclock secs (16.20 usr +  0.02 sys = 16.22 CPU) @ 61652.28/s (n=1000000)
     Memo2: 17 wallclock secs (16.13 usr +  0.03 sys = 16.16 CPU) @ 61881.19/s (n=1000000)
           Rate  Global Closure Lexical    Memo   Memo2
Global  37864/s      --     -0%     -4%    -39%    -39%
Closure 38037/s      0%      --     -3%    -38%    -39%
Lexical 39417/s      4%      4%      --    -36%    -36%
Memo    61652/s     63%     62%     56%      --     -0%
Memo2   61881/s     63%     63%     57%      0%      --