strat-B.hs

module Main where

import Control.Parallel
import Control.Parallel.Strategies (rseq, rpar, Strategy, using, runEval)
import Data.Time.Clock
import Text.Printf
import System.Environment


-- <<fib
fib :: Integer -> Integer
fib 0 = 1
fib 1 = 1
fib n = fib (n-1) + fib (n-2)
-- >>
--

main = do 

  t1 <- getCurrentTime
  let fib_one = fib 40
  printTimeSince t1
  print fib_one
  printTimeSince t1

  t2 <- getCurrentTime
  let pair = (fib 40, fib 40) `using` parPair
  printTimeSince t2
  print pair
  printTimeSince t2

parPair :: Strategy (a,b)
parPair (a,b) = do
  a' <- rpar a
  b' <- rpar b
  return (a',b')

printTimeSince t0 = do
  t1 <- getCurrentTime
  printf "time: %.2fs\n" (realToFrac (diffUTCTime t1 t0) :: Double)