McCarthy's 91 Function - Recursive

#!/usr/bin/perl -w

use strict;
use warnings;

my $n = <STDIN>;
chomp($n);

mprint($n, 1);

sub mprint {
    my $n = shift;
    my $level = shift;

    print tostring($n, $level)."\n";
    return if $level == 0;

    mprint($n+11, $level+1) if $n <= 100;
    mprint($n-10, $level-1) if $n > 100;
}

sub tostring {
    my $n = shift;
    my $level = shift;

    return "$n" if $level <= 0;
    return "M($n)" if $level == 1;
    return "M(".tostring($n, $level-1).")";
}