FizzBuzz_Correct.hs

module FizzBuzz where

import Data.Foldable (traverse_)

divisibleBy :: Int -> Int -> Bool
divisibleBy divisor x = x `mod` divisor == 0

data FizzResult v pt pf rt rf
  = Val v pf rf
  | Fizz pt rf
  | Buzz pf rt
  | FizzBuzz pt rt
  deriving (Show)

mkFizzBuzz :: (v -> Either pf pt) -> (v -> Either rf rt) -> v -> FizzResult v pt pf rt rf
mkFizzBuzz p1 p2 v =
  case (p1 v, p2 v) of
    (Right pt, Right rt) -> FizzBuzz pt rt
    (Right pt, Left  rf) -> Fizz pt rf
    (Left  pf, Right rt) -> Buzz pf rt
    (Left  pf, Left  rf) -> Val v pf rf

boolToEither :: Bool -> Either () ()
boolToEither True  = Right ()
boolToEither False = Left ()

type FizzBuzz = FizzResult Int () () () ()

fizzbuzz :: Int -> FizzBuzz
fizzbuzz =
  let divisibleBy' d x = boolToEither (divisibleBy d x)
  in mkFizzBuzz (divisibleBy' 3) (divisibleBy' 5)

main :: IO ()
main = traverse_ (print . fizzbuzz) [1 .. 100]