[commit: packages/containers] ghc-head: Avoid dependency on Applicative (ST s) instance ... (4f7bc51)

[git at git.haskell.org]

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

On branch  : ghc-head
Link       : http://git.haskell.org/packages/containers.git/commitdiff/4f7bc51fe6eb40f6b17bb2ee2906e0b03fdbab0d

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

commit 4f7bc51fe6eb40f6b17bb2ee2906e0b03fdbab0d
Author: Milan Straka <fox at ucw.cz>
Date:   Mon Oct 7 18:39:45 2013 +0200

    Avoid dependency on Applicative (ST s) instance ...
    
    ... present only in GHC 7.2+.


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

4f7bc51fe6eb40f6b17bb2ee2906e0b03fdbab0d
 Data/Graph.hs |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Data/Graph.hs b/Data/Graph.hs
index 3ddc4be..c5cdf4b 100644
--- a/Data/Graph.hs
+++ b/Data/Graph.hs
@@ -302,7 +302,10 @@ instance Functor (SetM s) where
 instance Applicative (SetM s) where
     pure x = SetM $ const (return x)
     {-# INLINE pure #-}
-    SetM f <*> SetM v = SetM $ \s -> f s <*> v s
+    SetM f <*> SetM v = SetM $ \s -> f s >>= (`fmap` v s)
+    -- We could also use the following definition
+    --   SetM f <*> SetM v = SetM $ \s -> f s <*> v s
+    -- but Applicative (ST s) instance is present only in GHC 7.2+
     {-# INLINE (<*>) #-}
 
 run          :: Bounds -> (forall s. SetM s a) -> a