Make Monad/Applicative instances MRP-friendly

This patch refactors pure/(*>) and return/(>>) in MRP-friendly way, i.e.
such that the explicit definitions for `return` and `(>>)` match the
MRP-style default-implementation, i.e.

  return = pure

and

  (>>) = (*>)

This way, e.g. all `return = pure` definitions can easily be grepped and
removed in GHC 8.1;

Test Plan: Harbormaster

Reviewers: goldfire, alanz, bgamari, quchen, austin

Reviewed By: quchen, austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1312

2 files changed, 4 insertions, 4 deletions

diff --git a/compiler/codeGen/StgCmmExtCode.hs b/compiler/codeGen/StgCmmExtCode.hs
index 2091d9b358..50015989e0 100644
--- a/compiler/codeGen/StgCmmExtCode.hs
+++ b/compiler/codeGen/StgCmmExtCode.hs
@@ -89,12 +89,12 @@ instance Functor CmmParse where
       fmap = liftM
 
 instance Applicative CmmParse where
-      pure = return
+      pure = returnExtFC
       (<*>) = ap
 
 instance Monad CmmParse where
   (>>=) = thenExtFC
-  return = returnExtFC
+  return = pure
 
 instance HasDynFlags CmmParse where
     getDynFlags = EC (\_ _ d -> do dflags <- getDynFlags
diff --git a/compiler/codeGen/StgCmmMonad.hs b/compiler/codeGen/StgCmmMonad.hs
index 3d055e75bb..3083bfffc4 100644
--- a/compiler/codeGen/StgCmmMonad.hs
+++ b/compiler/codeGen/StgCmmMonad.hs
@@ -118,12 +118,12 @@ instance Functor FCode where
   fmap f (FCode g) = FCode $ \i s -> case g i s of (# a, s' #) -> (# f a, s' #)
 
 instance A.Applicative FCode where
-      pure = return
+      pure = returnFC
       (<*>) = ap
 
 instance Monad FCode where
         (>>=) = thenFC
-        return = returnFC
+        return = A.pure
 
 {-# INLINE thenC #-}
 {-# INLINE thenFC #-}