Re: Give MonadTrans a QuantifiedConstraints superclass

On Wed, Jun 2, 2021 at 9:06 AM Zemyla 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 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. _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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