RosettaCodeData/Task/Ackermann-function/Perl-6/ackermann-function-1.pl6

sub A(Int $m, Int $n) {
    if    $m == 0 { $n + 1 }
    elsif $n == 0 { A($m - 1, 1) }
    else          { A($m - 1, A($m, $n - 1)) }
}