I thought about providing package ghc-transformers-instances, that will provide instances for transformers's type classes for user. So ghc-tf-instances will depend on current ghc, and current transformers that could be provided by user environment.

On Jan 21, 2015 7:15 PM, "Herbert Valerio Riedel" <hvriedel@gmail.com> wrote:
On 2015-01-21 at 16:51:55 +0100, Alexander V Vershilov wrote:

[...]

> As transformers usage are quite limited in ghc, and it's really relevant
> in ghc-bin, it's possible to duplicate the code, and provide required
> fixes in ghc-bin.cabal. As a result ghc uses it's own MonadIO, MonadControl
> and Strict State, and ghc-bin.cabal (ghc/*) uses ones from
> transformers.

...but doesn't this effectively mean that the instances provided by the
`ghc` package are of little use or rather can't be easily combined with
code that builds on top of the original `transformers` classes everyone
else uses?

Cheers,
  hvr