[Haskell-cafe] Re: applicative challenge

Conor McBride conor at strictlypositive.org
Mon May 4 20:50:06 EDT 2009

Hi Achim

On 5 May 2009, at 01:26, Achim Schneider wrote:

> Conor McBride <conor at strictlypositive.org> wrote:
>> Remember folks: Missiles need miffy!
> Hmmmm. Iff you have something like CoPointed or Foldable, you can
> thread your own, Applicative, tail back into yourself and decide what
> you are by inspecting it.

Yeah, Applicative on its own is kind of "effects without control",
or in Lindley-Wadler-Yallop parlance "oblivious". The fun starts
when you just chuck in a little bit more. Copointed might be
overdoing it. Even Alternative gives you quite a lot of control,
without going as far as Monad.

> That makes foldr the join of Hask itself, or something. Bear with me,
> I'm merely attempting to delurk our resident category theorists by
> giving them headaches.

Good luck


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