[Haskell-cafe] Turning Monoids into Categories

[David Feuer]

Thanks. That looks like the right thing. It's kind of a strange name
for it though, without the context. Basically,

Semi m = Constant . Constant m

I wonder if something similar by a different name might fit in transformers.

On Mon, Jun 22, 2015 at 1:13 PM, Patrick Chilton <chpatrick at gmail.com> wrote:
> Looks like Semi from semigroupoids:
> https://hackage.haskell.org/package/semigroupoids-5.0.0.2/docs/Data-Semigroupoid.html#t:Semi
>
> On Mon, Jun 22, 2015 at 5:51 PM, David Feuer <david.feuer at gmail.com> wrote:
>>
>> Is there a newtype defined in some normal sort of place for turning
>> Monoids into Categories? I'm looking for something like this:
>>
>> newtype ConstConst m a b = ConstConst m
>>
>> instance Monoid m => Category (ConstConst m) where
>>   id = ConstConst mempty
>>   ConstConst x . ConstConst y = ConstConst (x <> y)
>>
>> Thanks,
>> David Feuer
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>