[Haskell] Arrowに触れてみた(FizzBuzz)

最近、すこしずつ圏論の勉強と、Haskellの圏論関係のモジュールの勉強をしています　(*´σｰ｀)ｴﾍﾍ

練習問題として、 Control.Arrow を使って fizzbuzz を書いてみました

FizzBuzz

FizzBuzz.hs

import Control.Arrow

fizz :: Int -> Either Int String
fizz n = if n `mod` 3 == 0
           then Right "Fizz"
           else Left n


buzz :: Int -> Either Int String
buzz n = if n `mod` 5 == 0
           then Right "Buzz"
           else Left n


fizzbuzz :: Int -> Either Int String
fizzbuzz n = if n `mod` 15 == 0
               then Right "FizzBuzz"
               else Left n

fizzbuzzA :: Int -> String
fizzbuzzA = fizzbuzz >>> (buzz ||| Right) >>> (fizz ||| Right) >>> (show ||| id)


main :: IO ()
main = mapM_ (putStrLn . fizzbuzzA) [1..100] 

あとがき

関係ないけど、 Arrow の do構文の展開、めちゃクソ面倒くさくないですか

追記

こっちのほうがカッコ良いですね

FizzBuzz.hs

whenMultipleOf :: String -> Int -> Int -> Either Int String
whenMultipleOf str m n = if n `mod` m == 0
                           then Right str
                           else Left n

fizzbuzzA_ :: Int -> String
fizzbuzzA_ = "FizzBuzz" `whenMultipleOf` 15
         >>> "Buzz"     `whenMultipleOf` 5  ||| Right
         >>> "Fizz"     `whenMultipleOf` 3  ||| Right
         >>> show ||| id

Kleisli圏のArrowでもやってみた

FizzBuzz.hs

import Control.Arrow

fizz :: Kleisli (Either String) Int Int
fizz = Kleisli $ \n -> if n `mod` 3 == 0
                         then Left "Fizz"
                         else Right n


buzz :: Kleisli (Either String) Int Int
buzz  = Kleisli $ \n -> if n `mod` 5 == 0
                          then Left "Buzz"
                          else Right n


fizzbuzz :: Kleisli (Either String) Int Int
fizzbuzz = Kleisli $ \n -> if n `mod` 15 == 0
                             then Left "FizzBuzz"
                             else Right n

fizzbuzzA :: Int -> String
fizzbuzzA = either id show . runKleisli (fizzbuzz >>> buzz >>> fizz)


main :: IO ()
main = mapM_ (putStrLn . fizzbuzzA) [1..100]