const func integer: ackermann (in integer: m, in integer: n) is func
  result
    var integer: result is 0;
  begin
    if m = 0 then
      result := succ(n);
    elsif n = 0 then
      result := ackermann(pred(m), 1);
    else
      result := ackermann(pred(m), ackermann(m, pred(n)));
    end if;
  end func;