>文字列オブジェクトにインスタンス変数（状態）を持たせられるのが強みだなぁ。

-- String "has-a" Integer
data HasA = HasA String Integer
instance Show HasA where show (HasA s n) = if s == "" then show n else show s
fizz (HasA s n) = HasA (s ++ if mod n 3 == 0 then "Fizz" else "") n
buzz (HasA s n) = HasA (s ++ if mod n 5 == 0 then "Buzz" else "") n
gizz (HasA s n) = HasA (s ++ if mod n 7 == 0 then "Gizz" else "") n
main = print $ map (gizz . buzz . fizz . HasA "") [1,3,5,7,15,21,35,105]