FizzBuzz.hs

{-# LANGUAGE OverloadedStrings #-}
import Data.Monoid((<>))
import qualified Data.Text.Lazy as T
import qualified Data.Text.Lazy.Builder as B


-- The API of the fizz buzz

type Rule = B.Builder -> Int -> B.Builder

fizzBuzz' :: [Rule] -> Int -> B.Builder
fizzBuzz' rules i = foldl (\out rule -> out <> rule out i) "" rules


-- Helper function to build the rules

defaultRule :: Rule
defaultRule s n
  | s == mempty = B.fromLazyText $ T.pack (show n)
  | otherwise   = ""

makeRule :: Int -> T.Text -> Rule
makeRule d out _ n
  | mod n d == 0  = B.fromLazyText out
  | otherwise     = ""


-- Usage

testFizzBuzz :: IO ()
testFizzBuzz = do
  let fizzBuzz = fizzBuzz' [makeRule 3 "fizz", makeRule 5 "buzz", defaultRule]
  print $ map fizzBuzz [3, 5, 7, 15]