template-haskell: set explicit return=pure

This fixups a thinko in c6781a50

libraries/template-haskell/Language/Haskell/TH/PprLib.hs

@@ -158,6 +158,7 @@ instance Applicative PprM where
       (<*>) = ap
 
 instance Monad PprM where
+    return = pure
     m >>= k  = PprM $ \s -> let (x, s') = runPprM m s
                             in runPprM (k x) s'
 

libraries/template-haskell/Language/Haskell/TH/Syntax.hs

@@ -161,6 +161,7 @@ runQ (Q m) = m
 instance Monad Q where
   Q m >>= k  = Q (m >>= \x -> unQ (k x))
   (>>) = (*>)
+  return     = pure
   fail s     = report True s >> Q (fail "Q monad failure")
 
 instance Functor Q where