I need to use a list monad transformer. I've read that there are potential problems with ListT IO from Control.Monad.List, since IO isn't commutative, so I'm looking at ListT done right. But I'm getting some unexpected behavior.
Consider this simple test:
test = runListT $ do
x <- liftList [1..3]
liftIO $ print x
y <- liftList [6..8]
liftIO $ print (x,y)
Using Control.Monad.List:
Main> test
1
(1,6)
(1,7)
(1,8)
2
(2,6)
(2,7)
(2,8)
3
(3,6)
(3,7)
(3,8)
[(),(),(),(),(),(),(),(),()]
Using "ListT done right":
Main> test
1
(1,6)
Is this a problem with "ListT done right", or am I just using it wrong? Is there a preferred alternative?
Thanks!