Give MonadTrans a QuantifiedConstraints superclass

Viktor Dukhovni ietf-dane at
Wed Jun 2 15:48:48 UTC 2021

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. ]


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