deprecated Control.Monad.Trans.MSF.List ?

[madjestic]

Hey guys,

The examples of the paper are using this function:
https://hackage.haskell.org/package/dunai-0.11.0/docs/Control-Monad-Trans-MSF-List.html#v:widthFirst

ListT is also used in bearriver's parB = widthFirst . sequenceS

The module is marked as deprecated. What is the new alternative to the method using widthFirst as described in the paper and the examples?

Thanks!

[madjestic]

Doing some reading, I guess there are at least 2 options:
https://hackage.haskell.org/package/list-t
https://hackage.haskell.org/package/pipes

Should dunai use any of those?

[madjestic]

It looks like list-t package provides a trivial drop-in replacement for runListT, so the dunai example needs only a minor fix:

import ListT

-- we replace 
-- runListT :: forall (m :: * -> *) a. ListT m a -> m [a]
-- with
-- toList: : Monad m => ListT m a -> m [a]

widthFirst :: (Functor m, Monad m) => MSF (ListT m) a b -> MSF m a [b]
widthFirst msf = widthFirst' [msf]
  where
    widthFirst' msfs = MSF $ \a -> do
      (bs, msfs') <- unzip . concat <$> mapM (toList . flip unMSF a) msfs
      return (bs, widthFirst' msfs')

So the fix seems trivial, but then where does it need to go, since widthFirst is a part of (deprecated) Control.Monad.Trans.MSF.List ?

[ivanperez-keera]

Hi,

ListT is deprecated, but the module currently offered by dunai is not, and for the time being that's not going to change. We did talk about using list-t in the last. See: #36.

If this is a problem, we can discuss the alternatives.

I'm making this for now a discussion; if we agree on changing the implementation we can open an issue for that or re-classify this thread.