function ackermann(integer m, integer n)
  if m=0 then return n+1
  elsif m>0 and n=0 then return ackermann(m-1, 1)
  elsif m>0 and n>0 then return ackermann(m-1, ackermann(m,n-1))
  else return 0
  end if
  return 0
end function

? ackermann(0, 0)
? ackermann(3, 4)
? ackermann(3, 10)