On Wed, Jul 8, 2009 at 2:05 PM, <roconnor@theorem.ca> wrote:

On Wed, 8 Jul 2009, Edward Kmett wrote:

+1 in favor of generalizing Endo in Data.Monoid.

In my monoids library I have a Data.Monoid.Categorical that includes a 'GEndo' generalized endomorphism
over an arbitrary category and I would love to be able to remove it.

-Edward Kmett

I was looking for this in your lib, but I didn't find it.

Anyhow, I'm also in favour of generalizing Endo. I was being conservitive with my initial proposal.

Would we still have to pick a new name and then

type Endo a = NewEndoName (->) a

?

In Data.Monoid there is

newtype Endo a = Endo { appEndo :: a -> a }

instance Monoid (Endo a) where
mempty = Endo id
Endo f `mappend` Endo g = Endo (f . g)

and (->) is an instance of Category, so perhaps we should generalize Endo.

The name EndoCategory seems wrong, as this won't be an instance of Category.
Endomorphism?
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