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/cmm/CmmLint.hs b/compiler/cmm/CmmLint.hs
index 63a3ff5de3..a2ccfbeecf 100644
--- a/compiler/cmm/CmmLint.hs
+++ b/compiler/cmm/CmmLint.hs
@@ -217,7 +217,7 @@ instance Functor CmmLint where
       fmap = liftM
 
 instance Applicative CmmLint where
-      pure = return
+      pure a = CmmLint (\_ -> Right a)
       (<*>) = ap
 
 instance Monad CmmLint where
@@ -225,7 +225,7 @@ instance Monad CmmLint where
                                 case m dflags of
                                 Left e -> Left e
                                 Right a -> unCL (k a) dflags
-  return a = CmmLint (\_ -> Right a)
+  return = pure
 
 instance HasDynFlags CmmLint where
     getDynFlags = CmmLint (\dflags -> Right dflags)
diff --git a/compiler/cmm/PprC.hs b/compiler/cmm/PprC.hs
index c96b7076bf..76659caa8f 100644
--- a/compiler/cmm/PprC.hs
+++ b/compiler/cmm/PprC.hs
@@ -1005,12 +1005,12 @@ instance Functor TE where
       fmap = liftM
 
 instance Applicative TE where
-      pure = return
+      pure a = TE $ \s -> (a, s)
       (<*>) = ap
 
 instance Monad TE where
    TE m >>= k  = TE $ \s -> case m s of (a, s') -> unTE (k a) s'
-   return a    = TE $ \s -> (a, s)
+   return = pure
 
 te_lbl :: CLabel -> TE ()
 te_lbl lbl = TE $ \(temps,lbls) -> ((), (temps, Map.insert lbl () lbls))