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Michael Snoyman

13 Mar 2013 13 Mar '13

11:24 p.m.

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 I believe implementing this in terms of MonadTransControl[1] might be possible, but I was wondering if there's an already existing idiom for this. Michael [1] http://haddocks.fpcomplete.com/fp/7.4.2/20130301-40/monad-control/Control-Mo...

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Ross Paterson

9 Apr 9 Apr

8:45 a.m.

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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Hiromi ISHII

8:52 a.m.

Hi there, Gabriel's `mmorph` library [1] provides such abstraction, i.e. `MMonad` type-class and `squash` function. [1]: http://hackage.haskell.org/package/mmorph

On 2018/04/09 21:45, Ross Paterson wrote:

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. _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

-- Hiromi ISHII konn.jinro@gmail.com Doctoral program in Mathematics, University of Tsukuba

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Daniel Díaz Casanueva

9:41 a.m.

+1 on adding this to transformers. 2018-04-09 14:45 GMT+02:00 Ross Paterson :

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. _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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David Feuer

11 Apr 11 Apr

7:17 a.m.

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 wrote:

+1 on adding this to transformers.

2018-04-09 14:45 GMT+02:00 Ross Paterson :

...
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. _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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Ross Paterson

10:03 a.m.

On Wed, Apr 11, 2018 at 11:17:54AM +0000, David Feuer wrote:

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.

Since transformers is targeted at standard Haskell, it wouldn't be able to define MFunctor or embed. It would have to be something like class (MonadTrans t) => MonadMonad t where joinT :: Monad m => t (t m) a -> t m a

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Daniel Díaz Casanueva
David Feuer
Hiromi ISHII
Michael Snoyman
Ross Paterson