Re: [Haskell-cafe] Re: IO in lists

Dan Piponi wrote:

No, definitely the new one. The old one is:

newtype ListT m a = ListT { runListT :: m [a] }

which treats the entire list as one uninterleavable lump.

The new one is:

data MList' m a = MNil | a `MCons` MList m a type MList m a = m (MList' m a) newtype ListT m a = ListT { runListT :: MList m a }

OK.

Note the definition of MList' is isomorphic to a use of Maybe.

Yes, and in fact http://www.haskell.org/hawiki/ListTDoneRight_2fAlternative1 uses exactly your type. But the old broken ListT happens to work fine here. See my earlier post in this thread. Regards, Yitz