[Haskell-cafe] Join a transformer

Hiromi ISHII konn.jinro at gmail.com
Mon Apr 9 12:52:48 UTC 2018

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 <R.Paterson at city.ac.uk> 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.
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-- Hiromi ISHII
konn.jinro at gmail.com
Doctoral program in Mathematics,
University of Tsukuba

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