data Stream a = Cons a (Stream a)

instance Show a => Show (Stream a) where
show = take 20 . streamToList

streamToList :: Stream a -> [a]
streamToList (Cons x xs) = [x] ++ streamToList xs

-- generates a stream containing infinitely many copies of the
-- given elemen

streamRepeat :: a -> Stream a
streamRepeat x = Cons x $ streamRepeat x