fork download
copy 
  1. import Data.IORef
  2. import System.IO.Unsafe (unsafePerformIO)
  3.  
  4. getGlobalVar :: IO Int
  5. setGlobalVar :: Int -> IO ()
  6.  
  7. (getGlobalVar,setGlobalVar) = unsafePerformIO $ do
  8.     x_ref <- newIORef 0
  9.     return (readIORef x_ref, writeIORef x_ref)
  10.  
  11. foo = do v <- (+1) <$> getGlobalVar
  12.          setGlobalVar v
  13.          return v
  14.  
  15. bar = do v <- (*2) <$> getGlobalVar
  16.          setGlobalVar v
  17.          return v
  18.  
  19. main = do
  20. 	print =<< foo
  21. 	print =<< bar
  22. 	print =<< foo
  23. 	print =<< bar
  24.  
Success #stdin #stdout 0s 8388607KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
1
2
3
6
https://ideone.com/1KMVDj
language:
Haskell (ghc 8.4.4)
created:
6 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!