Generalised FizzBuzz

FizzBuzz.hs

{-# LANGUAGE ScopedTypeVariables #-}
module Main where

import Control.Monad (forM_)
import Data.Maybe (fromMaybe)

generalisedFizzBuzz
    :: forall a f m
     . (Foldable f, Semigroup m)
    => (a -> m) -> (a -> a -> Bool) -> f (a, m) -> a -> m
generalisedFizzBuzz def pred conditions x = fromMaybe (def x) $ evaluate x
  where
    evaluate :: a -> Maybe m
    evaluate = foldMap wrap conditions

    wrap :: (a, m) -> a -> Maybe m
    wrap (x, r) y
        | pred x y = Just r
        | otherwise = Nothing

fizzBuzz :: (Integral n, Show n) => n -> String
fizzBuzz = generalisedFizzBuzz show divides [(3, "Fizz"), (5, "Buzz")]
  where
    divides :: Integral n => n -> n -> Bool
    divides x n = n `mod` x == 0

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