On Wed, Jun 2, 2021 at 9:06 AM Zemyla <zemyla@gmail.com> wrote:

I feel like instead, MonadTrans should have a function

(>>==) :: Monad m => t m a -> (a -> t m b) -> t m b

This strikes me as a strictly worse outcome. Now you get coherence laws relating (>>==) to a (>>=) that may or may not exist that you have to keep track of, but get nothing enforcing anything, can't delegate to code that builds off Monad, leading to random code duplication, and users are hoist on the horns of the dilemma of using (>>=) or (>>==) with different constraints in each circumstance.

-Edward

That way, it can prove it's a Monad while still staying Haskell 98.

On Wed, Jun 2, 2021, 10:51 Viktor Dukhovni <ietf-dane@dukhovni.org> wrote:
On Wed, Jun 02, 2021 at 07:27:28AM +0200, Henning Thielemann wrote:

> So far, 'transformers' is mostly Haskell 98. This is why I prefer it
> to 'mtl'. Wouldn't it be enough to add this extension to 'mtl'? I see
> that 'mtl' re-uses the MonadTrans class from 'transformers' but maybe
> it should define its own class with the quantified constraints then.

I don't think that having two incompatible MonadTrans classes would
constitute progress. Older versions of the transformers library (which
is by now quite stable) will continue to be available, for anyone who
wants to use a Haskell '98 (ish?) version.

[ FWIW, I don't know what you mean by "is mostly Haskell '98", I'd
expect that to be a strict binary choice: is or isn't. ]

--
Viktor.
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