HQ9F+

Main.hs

module Main where

import Control.Monad
import Control.Exception
import Data.IORef

main :: IO ()
main = loop `catch` ignore
    where
        loop :: IO ()
        loop = forever $ do
            acc <- newIORef 0
            src <- getLine
            forM_ src $ \com -> run com src acc
        ignore :: SomeException -> IO ()
        ignore _ = return ()

run :: Char -> String -> IORef Int -> IO ()
run com src acc =
    case com of
        'H' -> putStrLn "Hello, world!"
        'Q' -> putStrLn src
        '9' -> beer 99
        'F' -> fizzbuzz
        '+' -> modifyIORef acc (+ 1)
        _   -> return ()

beer :: Int -> IO ()
beer 1 =
    let text =
            "1 bottle of beer\n" ++
            "you take it down, pass it around,\n" ++
            "no more bottles of beer on the wall.\n"
    in putStrLn text
beer n =
    let text =
            show n ++ " bottles of beer\n" ++
            "you take one down, pass it around,\n" ++
            show (n - 1) ++ " bottles of beer on the wall.\n"
    in do
        putStrLn text
        beer (n - 1)

fizzbuzz :: IO ()
fizzbuzz =
    forM_ [1 .. 100] $ \i ->
        if i `mod` 15 == 0 then
            putStrLn "FizzBuzz"
        else if i `mod` 3 == 0 then
            putStrLn "Fizz"
        else if i `mod` 5 == 0 then
            putStrLn "Buzz"
        else
            print i