[commit: ghc] master: Add `MonadPlus IO` and `Alternative IO` instances (b62605e)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/b62605e53c167719b3bf8842eba628061cf22dd1/ghc

>---------------------------------------------------------------

commit b62605e53c167719b3bf8842eba628061cf22dd1
Author: Herbert Valerio Riedel <hvr at gnu.org>
Date:   Tue Nov 3 16:12:18 2015 -0600

    Add `MonadPlus IO` and `Alternative IO` instances
    
    This requires adding a new primitive `mplusIO` to `GHC.IO`
    
    Update transformers submodule to accomodate extant orphan instances.
    
    Reviewed By: austin, bgamari
    
    Differential Revision: https://phabricator.haskell.org/D1148
    
    GHC Trac Issues: #10755


>---------------------------------------------------------------

b62605e53c167719b3bf8842eba628061cf22dd1
 libraries/base/GHC/Base.hs    |  8 +++++++-
 libraries/base/GHC/IO.hs      | 10 ++++++++--
 libraries/base/GHC/IO.hs-boot |  2 +-
 libraries/base/changelog.md   |  3 +++
 libraries/transformers        |  2 +-
 5 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/libraries/base/GHC/Base.hs b/libraries/base/GHC/Base.hs
index 619acac..189e480 100644
--- a/libraries/base/GHC/Base.hs
+++ b/libraries/base/GHC/Base.hs
@@ -111,7 +111,7 @@ import GHC.CString
 import GHC.Magic
 import GHC.Prim
 import GHC.Err
-import {-# SOURCE #-} GHC.IO (failIO)
+import {-# SOURCE #-} GHC.IO (failIO,mplusIO)
 
 import GHC.Tuple ()     -- Note [Depend on GHC.Tuple]
 import GHC.Integer ()   -- Note [Depend on GHC.Integer]
@@ -1079,6 +1079,12 @@ instance  Monad IO  where
     (>>=)     = bindIO
     fail s    = failIO s
 
+instance Alternative IO where
+    empty = failIO "mzero"
+    (<|>) = mplusIO
+
+instance MonadPlus IO
+
 returnIO :: a -> IO a
 returnIO x = IO $ \ s -> (# s, x #)
 
diff --git a/libraries/base/GHC/IO.hs b/libraries/base/GHC/IO.hs
index 9fa0aff..1e8c74e 100644
--- a/libraries/base/GHC/IO.hs
+++ b/libraries/base/GHC/IO.hs
@@ -23,7 +23,7 @@
 -----------------------------------------------------------------------------
 
 module GHC.IO (
-        IO(..), unIO, failIO, liftIO,
+        IO(..), unIO, failIO, liftIO, mplusIO,
         unsafePerformIO, unsafeInterleaveIO,
         unsafeDupablePerformIO, unsafeDupableInterleaveIO,
         noDuplicate,
@@ -45,7 +45,7 @@ import GHC.ST
 import GHC.Exception
 import GHC.Show
 
-import {-# SOURCE #-} GHC.IO.Exception ( userError )
+import {-# SOURCE #-} GHC.IO.Exception ( userError, IOError )
 
 -- ---------------------------------------------------------------------------
 -- The IO Monad
@@ -292,6 +292,12 @@ catchAny :: IO a -> (forall e . Exception e => e -> IO a) -> IO a
 catchAny (IO io) handler = IO $ catch# io handler'
     where handler' (SomeException e) = unIO (handler e)
 
+
+mplusIO :: IO a -> IO a -> IO a
+mplusIO m n = m `catchIOError` \ _ -> n
+    where catchIOError :: IO a -> (IOError -> IO a) -> IO a
+          catchIOError = catchException
+
 -- | A variant of 'throw' that can only be used within the 'IO' monad.
 --
 -- Although 'throwIO' has a type that is an instance of the type of 'throw', the
diff --git a/libraries/base/GHC/IO.hs-boot b/libraries/base/GHC/IO.hs-boot
index fb0dd96..88b09aa 100644
--- a/libraries/base/GHC/IO.hs-boot
+++ b/libraries/base/GHC/IO.hs-boot
@@ -6,4 +6,4 @@ module GHC.IO where
 import GHC.Types
 
 failIO :: [Char] -> IO a
-
+mplusIO :: IO a -> IO a -> IO a
diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md
index fe65399..7fb4d78 100644
--- a/libraries/base/changelog.md
+++ b/libraries/base/changelog.md
@@ -85,6 +85,9 @@
 
   * The `MINIMAL` definition of `ArrowChoice` is now `left OR (+++)`.
 
+  * Add `MonadPlus IO` and `Alternative IO` instances
+    (previously orphans in `transformers`) (#10755)
+
 ## 4.8.2.0  *Oct 2015*
 
   * Bundled with GHC 7.10.3
diff --git a/libraries/transformers b/libraries/transformers
index 0c7207e..5ccb747 160000
--- a/libraries/transformers
+++ b/libraries/transformers
@@ -1 +1 @@
-Subproject commit 0c7207e9702afb5344cc33892eb6da9126a85cf3
+Subproject commit 5ccb747e67d579e3f212fd3526469c35282e532e