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

Having coerce (!) show up in such a commonly used type class is a bit alarming. Was there a libraries discussion about this? At least we should add some docs to the method. On Wed, Sep 25, 2013 at 12:37 AM, wrote:

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

On branch : master Link : http://ghc.haskell.org/trac/ghc/changeset/3da4fd92e005cb9348ab2852d9268ad61a...

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commit 3da4fd92e005cb9348ab2852d9268ad61ae1b347 Author: Austin Seipp 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 Signed-off-by: Austin Seipp

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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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