sub partition {
    my ( $m, $n ) = @_;
    die "bad inputs" if $m <= 0 or $n <= 0;
    print "P($m,$n) = ";
    if ( $m == 1 or $n == 1 ) {
        say 1;
        return 1;
    }
    if ( $m < $n ) {
        say "P($m,$m)";
        return partition( $m, $m );
    }
    if ( $m == $n ) {
        say "1 + P($m,", $m - 1, ")";
        return 1 + partition( $m, $m - 1 );
    }
    if ( $m > $n ) {
        say "P($m,", $n - 1, ") + P(", $m - $n, ",$n)";
        return partition( $m, $n - 1 ) + partition( $m - $n, $n );
    }
    die "impossible!";
}

MAIN: {
    my ( $m, $n ) = @ARGV;
    $n ||= $m;
    say partition( $m, $n );
}