gistfile1.hs

escapes1 :: RealFloat a => Int -> Complex a -> Bool
escapes1 i c = any ((>) 2 . magnitude) (take i ps)
   where ps = iterate p (0 :+ 0)
         p = \z -> c + z^(2 :: Int)

escapes2 :: RealFloat a => Int -> Complex a -> Bool
escapes2 i c = escapes2' i c (0 :+ 0)

escapes2' :: RealFloat a => Int -> Complex a -> Complex a -> Bool
escapes2' 0 _ _ = False
escapes2' !i !c !z = 
  if magnitude z' > 2 then True else escapes2' (pred i) c z'
  where z' = c + z^(2 :: Int)