[commit: packages/base] master: Add fmapCoerce to Functor class. (3da4fd9)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/3da4fd92e005cb9348ab2852d9268ad61ae1b347/base

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

commit 3da4fd92e005cb9348ab2852d9268ad61ae1b347
Author: Austin Seipp <austin at well-typed.com>
Date:   Tue Sep 24 23:20:35 2013 -0500

    Add fmapCoerce to Functor class.
    
    This allows coercions to work under functors that are not locally known.
    
    Authored-by: Edward Kmett <ekmett at gmail.com>
    Signed-off-by: Austin Seipp <austin at well-typed.com>


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

3da4fd92e005cb9348ab2852d9268ad61ae1b347
 GHC/Base.lhs |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/GHC/Base.lhs b/GHC/Base.lhs
index d876202..55172af 100644
--- a/GHC/Base.lhs
+++ b/GHC/Base.lhs
@@ -105,7 +105,6 @@ module GHC.Base
         module GHC.Err          -- import it explicitly
   )
         where
-
 import GHC.Types
 import GHC.Classes
 import GHC.CString
@@ -186,6 +185,9 @@ class  Functor f  where
     (<$)        :: a -> f b -> f a
     (<$)        =  fmap . const
 
+    fmapCoerce :: Coercible a b => f a -> f b
+    fmapCoerce = fmap coerce
+
 {- | The 'Monad' class defines the basic operations over a /monad/,
 a concept from a branch of mathematics known as /category theory/.
 From the perspective of a Haskell programmer, however, it is best to