Hi, Just some easy fun: $> ghci Prelude> :l busyBeaver.hs Prelude> map snd busyBeaver [A,B,A,C,B,A,B,B,B,B,B,A,C,Halt] Best, Maurício -- | busyBeaver.hs data State = A | B | C | Halt deriving Show data Value = Blank | NonBlank type Tape = (Integer -> Value) moveRight tape = \n -> tape $ n - 1 moveLeft tape = \n -> tape $ n + 1 (write tape) n = if n == 0 then NonBlank else tape n table :: (Tape,State) -> (Tape,State) table (tape,state) = case (tape 0,state) of (Blank,A) -> ((moveRight . write) tape , B) (NonBlank,A) -> ((moveLeft . write) tape , C) (Blank,B) -> ((moveLeft . write) tape , A) (NonBlank,B) -> ((moveRight . write) tape , B) (Blank,C) -> ((moveLeft . write) tape , B) (NonBlank,C) ->((moveRight . write) tape , Halt) (_,Halt) -> (tape,Halt) busyBeaver = bb (const Blank,A) where bb t@(_,Halt) = t:[] bb t = t:(bb $ table t)