If something like MMonad gets added to transformers, then its MFunctor version should really be double-ended to work with things like the final version of FreeT.

On Mon, Apr 9, 2018, 9:41 AM Daniel Díaz Casanueva <dhelta.diaz@gmail.com> wrote:
+1 on adding this to transformers.

2018-04-09 14:45 GMT+02:00 Ross Paterson <R.Paterson@city.ac.uk>:
On Thu, Mar 14, 2013 at 05:24:23AM +0200, Michael Snoyman wrote:
>    I'm wondering if this pattern exists and has a name. We have the
>    concept of joining a Monad:
>    join :: Monad m => m (m a) -> ma
>    How about joining a monad transformer?
>    joinT :: (Monad m, MonadTrans t) => t (t m) a -> t m a

This is a monad in the category of monads.  Moggi discusses them in
"An Abstract View of Programming Languages", including which transformers
have joinT.  I was thinking of adding the class to the transformers package.
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