Add Control.Monad.IO.Class from transformers to base

[RyanGlScott]

(As proposed in a Haskell libraries mailing list thread ​here).

This Trac issue addresses one of the two suggestions made in the proposal, i.e., moving Control.Monad.IO.Class from transformers to base. (The second, introducing a MonadIO Q instance in template-haskell, can be dealt with depending on the result of this.)

Conceptually, this change is very similar in spirit to #9664—the MonadIO class is a Haskell98 typeclass that has proven to be widely useful in abstracting IO-based functions into a type signature that can be used with monad transformer stacks. Moving MonadIO's module into base would allow more widespread use without incurring a transformers dependency, and it could provide a first step for generalizing more base functions from IO to MonadIO.

[Ben Gamari <ben@…>]

In fff02548/ghc:

Move Control.Monad.IO.Class to base from transformers

See Trac #10773

Remove Control.Monad.IO.Class from `transformers`. Updates
`transformers` submodule.

See Trac #10773

Test Plan: ./validate

Reviewers: ekmett, hvr, bgamari, austin

Reviewed By: hvr, bgamari, austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1147

GHC Trac Issues: #10773

[bgamari]

This has been merged.