{-# LANGUAGE RecordWildCards #-}

import Data.IORef
import System.Clock


data Timer =
    Timer {
      _timerRef  :: !(IORef TimeSpec),
      _timerType :: !Clock
    }


newTimer :: Clock -> IO Timer
newTimer _timerType =
    fmap (\_timerRef -> Timer{..})
         (getTime _timerType >>= newIORef)


timed :: Timer -> IO a -> IO a
timed Timer{..} action = do
    t0 <- getTime _timerType
    r <- action
    t1 <- getTime _timerType
    let dt = t1 - t0
    r <$ atomicModifyIORef' _timerRef (\t -> (t + dt, ()))