gistfile1.hs

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeFamilies #-}

import Control.Concurrent (threadDelay)
import Control.LVish
import Control.LVish.DeepFrz
import Control.LVish.Internal (liftIO)
import Data.LVar.IVar
import Data.LVar.Counter
import Data.Word

lessthan :: (HasGet e, HasPut e, HasBump e) => Word -> Par e s (IVar s Bool)
lessthan w = do
  r <- new
  c <- newCounter 0
  fork $ (waitThresh c w >> put r True)
  fork $ (doSomeWork c)
  -- note that this is just `return r`, not `get r`
  return r

doSomeWork c = do
  liftIO $ threadDelay 1000000
  increment c 3

main = do
  let v = runParThenFreeze $ lessthan 4
  print $ case (fromIVar v) of
    Nothing -> False
    Just True -> True