Simple alarm, "sbatty in 10s", set an alarm in 10s

sbatty.hs

{-# LANGUAGE DeriveGeneric, OverloadedStrings #-}

module Main where

import Control.Applicative
import Control.Concurrent
import Data.Default ( def )
import Data.Serialize
import System.Environment ( getArgs )
import System.Daemon
import System.Process

import GHC.Generics

data Command = Add Int | Error
    deriving (Generic, Show)

data Response = Ok | Failed
    deriving (Generic, Show)

instance Serialize Command
instance Serialize Response

beep = sequence_ [b, b, b]
  where 
    b = system "/usr/bin/afplay /Users/ga2arch/Music/beep.wav"

handleCommand :: Command -> IO Response
handleCommand (Add t) = do 
    forkIO $ do
        threadDelay t
        beep

    return Ok

handleCommand Error = return Failed

microseconds time = 
    case (last time) of
        's' -> 1  * 10^6
        'm' -> 6  * 10^7
        'h' -> 36 * 10^8

parseCmd :: [String] -> Command
parseCmd ("in":time:_) = Add $ (read $ init time) * (microseconds time)
parseCmd _ = Error

main :: IO ()
main = do
    ensureDaemonRunning "sbatty" def { daemonPort = 6666 } handleCommand
    cmd <- parseCmd <$> getArgs :: IO Command
    res <- runClient "localhost" 6666 cmd
    print (res :: Maybe Response)