processing-for-haskell-0.1.0.0: src/Graphics/Proc/Core/State/Elements/Time.hs

module Graphics.Proc.Core.State.Elements.Time(
    TimeState(..), initTimeState, TimeInterval, getDuration
) where

import Data.Time.Clock
import Control.Monad.Trans.State.Strict

-- | Time duration in seconds.
type TimeInterval = Float

data TimeState = TimeState 
  { timeLast      :: UTCTime
  , timeStart     :: UTCTime }

initTimeState = fmap (\x -> TimeState x x) getCurrentTime   

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getDuration :: StateT TimeState IO TimeInterval
getDuration = StateT $ \s -> do
    let prevTime = timeLast s
    now <- getCurrentTime
    let dt = fromRational $ toRational $ diffUTCTime now prevTime
    return (dt, s { timeLast = now })