RosettaCodeData/Task/Ackermann-function/Lucid/ackermann-function.lucid

ack(m,n)
 where
  ack(m,n) = if m eq 0 then n+1
                       else if n eq 0 then ack(m-1,1)
                                      else ack(m-1, ack(m, n-1)) fi
                       fi;
 end