Fizzbuzz1.hs

module Main where

fizzBuzz :: Int -> IO ()
fizzBuzz n | n `mod` 5 == 0 && n `mod` 3 == 0 = putStrLn "Fizz Buzz"
           | n `mod` 5 == 0 = putStrLn "Buzz"
           | n `mod` 3 == 0 = putStrLn "Buzz"
           | otherwise = return ()

runManyActions [] = return []
runManyActions (x:xs) = do
  y <- x
  ys <- runManyActions xs
  return (y:ys)


main :: IO ()
main = do
  let actions = runManyActions $ map fizzBuzz [1..50]
  results <- actions
  return ()

Fizzbuzz2.hs

module Main where

fizzBuzz :: Int -> IO ()
fizzBuzz n | n `mod` 5 == 0 && n `mod` 3 == 0 = putStrLn "Fizz Buzz"
           | n `mod` 5 == 0 = putStrLn "Buzz"
           | n `mod` 3 == 0 = putStrLn "Buzz"
           | otherwise = return ()

main :: IO ()
main = do
  let ns = [1..100]
  runFizzBuzz ns

runFizzBuzz :: [Int] -> IO ()
runFizzBuzz [] = return ()
runFizzBuzz (x:xs) = do
  fizzBuzz x
  runFizzBuzz xs

Fizzbuzz3.hs

module Main where

fizzBuzz :: Int -> Maybe String
fizzBuzz n | n `mod` 5 == 0 && n `mod` 3 == 0 = Just "Fizz Buzz"
           | n `mod` 5 == 0 = Just "Buzz"
           | n `mod` 3 == 0 = Just "Fizz"
           | otherwise = Nothing

main :: IO ()
main = do
  let ns = [1..100]
  let messages = dropMaybes $ map fizzBuzz ns
  mapM putStrLn messages
  return ()


dropMaybes [] = []
dropMaybes (x:xs) = 
  case x of
    Nothing -> dropMaybes xs
    Just y -> y : dropMaybes xs