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

4 files changed, 40 insertions, 0 deletions

diff --git a/libraries/base/Control/Monad/IO/Class.hs b/libraries/base/Control/Monad/IO/Class.hs
new file mode 100644
index 0000000000..b2c419c3a7
--- /dev/null
+++ b/libraries/base/Control/Monad/IO/Class.hs
@@ -0,0 +1,36 @@
+{-# LANGUAGE Safe #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Control.Monad.IO.Class
+-- Copyright   :  (c) Andy Gill 2001,
+--                (c) Oregon Graduate Institute of Science and Technology, 2001
+-- License     :  BSD-style (see the file LICENSE)
+--
+-- Maintainer  :  R.Paterson@city.ac.uk
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- Class of monads based on @IO@.
+-----------------------------------------------------------------------------
+
+module Control.Monad.IO.Class (
+    MonadIO(..)
+  ) where
+
+-- | Monads in which 'IO' computations may be embedded.
+-- Any monad built by applying a sequence of monad transformers to the
+-- 'IO' monad will be an instance of this class.
+--
+-- Instances should satisfy the following laws, which state that 'liftIO'
+-- is a transformer of monads:
+--
+-- * @'liftIO' . 'return' = 'return'@
+--
+-- * @'liftIO' (m >>= f) = 'liftIO' m >>= ('liftIO' . f)@
+
+class (Monad m) => MonadIO m where
+    -- | Lift a computation from the 'IO' monad.
+    liftIO :: IO a -> m a
+
+instance MonadIO IO where
+    liftIO = id
diff --git a/libraries/base/base.cabal b/libraries/base/base.cabal
index 326f4579fd..7a0ef9865a 100644
--- a/libraries/base/base.cabal
+++ b/libraries/base/base.cabal
@@ -115,6 +115,7 @@ Library
         Control.Monad
         Control.Monad.Fix
         Control.Monad.Instances
+        Control.Monad.IO.Class
         Control.Monad.ST
         Control.Monad.ST.Lazy
         Control.Monad.ST.Lazy.Safe
diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md
index 34493ac47e..ff03562c33 100644
--- a/libraries/base/changelog.md
+++ b/libraries/base/changelog.md
@@ -56,6 +56,9 @@
   * Made `PatternMatchFail`, `RecSelError`, `RecConError`, `RecUpdError`,
     `NoMethodError`, and `AssertionFailed` newtypes (#10738)
 
+  * New module `Control.Monad.IO.Class` (previously provided by `transformers`
+    package). (#10773)
+
   * The `Generic` instance for `Proxy` is now poly-kinded (#10775)
 
   * add `Data.List.NonEmpty` and `Data.Semigroup` (to become
diff --git a/libraries/transformers b/libraries/transformers
-Subproject 078c7daf36ea1fa1ecb63b04dbe667a443e1304
+Subproject 0c7207e9702afb5344cc33892eb6da9126a85cf