​Thanks! I have a problem though. I read about automatic derivation of an NFData instance. I have GHC version 7.10.2. I tried the code below, but I get

Can't make a derived instance of Generic RawMidiEvent

  You need DeriveGeneric to derive an instance of this class. 

In the data declaration for 'RawMidiEvent'

{-# LANGUAGE DeriveGeneric, DeriveAnyClass #-}

import GHC.Generics (Generic)
import Control.DeepSeq

data RawMidiEvent = RawMidiEvent 
  { rmeStream :: Int
  , rmeChan :: Int 
  , rmeStatus :: Int 
  , rmeData1 :: Int
  , rmeData2 :: Int
  }
  deriving (Show,Eq,Generic,NFData)