Hi,
Does it make sense to declare a transparent identity instance for
Functor, Applicative, Monad, etc?
For example, I might want to generalize ($) = (*) where
($) :: (a - b) - a - b
(*) :: (Functor f) = f (a - b) - f a - f b
The traditional definition makes Identity a newtype:
newtype
On Sun, Nov 28, 2010 at 15:59, Jafet jafet.vi...@gmail.com wrote:
But using this instance becomes unwieldy. If using Identity was
transparent, eg. if it was a type synonym
{-# LANGUAGE TypeSynonymInstances #-}
type Identity a = a
instance Applicative Identity where
-- something like
On 11/28/10 9:59 AM, Jafet wrote:
But GHC does not accept type synonym instances unless they are fully applied.
That's precisely the problem, and why a newtype is used. More than GHC
implementation details, there's the deeper problem that allowing general
type-level functions causes
