Strategien

import Control.Parallel.Strategies
main = do
  let top = 100000000 ; threads = 4
  print $ psum $ do 
    t <- [ 0 .. threads - 1 ] 
    return $ sum [ t, t + threads .. top - 1 ]
psum []  = 0          
psum (x : xs) = (x `using` rpar)  + psum xs