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

[Simon Peyton-Jones]

This is great, but does needs some explanatory material, on the Haskell wiki or Trac.

Simon

| -----Original Message-----
| From: ghc-commits [mailto:ghc-commits-bounces at haskell.org] On Behalf Of
| git at git.haskell.org
| Sent: 25 September 2013 05:38
| To: ghc-commits at haskell.org
| Subject: [commit: packages/base] master: Add fmapCoerce to Functor
| class. (3da4fd9)
| 
| Repository : ssh://git@git.haskell.org/base
| 
| On branch  : master
| Link       :
| http://ghc.haskell.org/trac/ghc/changeset/3da4fd92e005cb9348ab2852d9268a
| d61ae1b347/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
| 
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