[Haskell-cafe] Re: IO in lists

[Yitzchak Gale]

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