Hello, I'm having a problem with GHC. 

When I compile the code bellow it does nothing, but If I try to use ghci it works normally. 

it seems a simple problem, but I can't understand.

Thanks for the help

Mauricio

import System.IO

import Control.Concurrent

import Data.List 

main = do   

     input <- newMVar  [1..30000]

     ia <- newEmptyMVar

     ib <- newEmptyMVar

     ic <- newEmptyMVar

     

     forkIO $ do x <- readMVar input

                 putMVar ia x

               

     forkIO $ do a <- readMVar ia

                 putMVar ib ( sum a )

     

     forkIO $ do a <- readMVar ia

                 putMVar ic ( reverse a )

     

     forkIO $ do b <- readMVar ib

                 c <- readMVar ic

                 print b 

                 print c