FizzBuzz: algebraic data types help you represent disjoint events as disjoint sets.

FizzBuzz.hs

#!/usr/bin/env runhaskell
module FizzBuzz where

import Control.Monad

data FizzBuzz = Otherwise Int | Fizz | Buzz | FizzBuzz deriving (Show)

fizzBuzz :: Int -> FizzBuzz
fizzBuzz i = case (i `mod` 3 == 0, i `mod` 5 == 0) of
    (False, False) -> Otherwise i
    (True, False) -> Fizz
    (False, True) -> Buzz
    (True, True) -> FizzBuzz

main :: IO ()
main = forM_ [1..100] $ print . fizzBuzz