Another way to do it would be newtype Words = Words { getWords :: String } instance Semigroup Words where Words a <> Words b = Words (a <> " " <

Another way to do it would be newtype Words = Words { getWords :: String } instance Semigroup Words where Words a <> Words b = Words (a <> " " <> b) instance Monoid Words where mempty = Words mempty fizzbuzz i = maybe (show i) (<> "!") . fmap getWords . mconcat $ [ Words "fizz" <$ guard (rem i 3 == 0) , Words "buzz" <$ guard (rem i 5 == 0) ] but at this point I agree lists might be more clear.