Pointed [Re: 2014 Applicative => Monad proposal]

[Andreas Abel]

Pointed is a superclass of Applicative, taking the role of pure, but not 
related to Functor.  I do not see the problem.

On 24.05.2013 19:59, Dan Doel wrote:
> Where is Pointed supposed to live in the hierarchy? For instance,
> someone mentioned Set. But Set is not eligible to have a Functor instance.
>
> So do we just have Pointed type functions that aren't necessarily
> Functors? And if they are Functors/Applicatives/Monads they're supposed
> to behave nicely?
>
> And if not, then several collections are excluded from being Pointed,
> and I'm not entirely sure which collections you're using. Just many
> different sequence types?
>
>
> On Fri, May 24, 2013 at 1:02 PM, Andreas Abel <andreas.abel at ifi.lmu.de
> <mailto:andreas.abel at ifi.lmu.de>> wrote:
>
>     I do not use Pointed a lot, but a situation where it comes natural
>     is when I want to emit elements into a collection f.  Then I need
>
>        Pointed f    -- to emit a single element
>        Monoid (f a) -- to join two collections
>
>     Using Applicative or Monad is overdoing it.
>
>     Maybe you have a better suggestion how to organize my task which I
>     have not considered yet...
>
>     Cheers, Andreas
>
>     On 24.05.2013 17 <tel:24.05.2013%2017>:28, Roman Cheplyaka wrote:
>
>         I completely agree with Edward here.
>
>         * Edward Kmett <ekmett at gmail.com <mailto:ekmett at gmail.com>>
>         [2013-05-24 11:20:51-0400]
>
>             For the record I'm actually -1 on including Pointed.
>
>             My experience is that there are very few uses for the class
>             that permit you
>             to reason about your code without one-off ad hoc reasoning
>             based on the
>             particular instance you are given. Now, the Apply and Bind
>             classes on the
>             other hand... =) Though, to be fair, I couldn't seriously
>             propose including
>             either of those, either. Even I can't be bothered to
>             instantiate them all
>             the time!
>
>             -Edward
>
>
>             On Fri, May 24, 2013 at 11:13 AM, Andreas Abel
>             <andreas.abel at ifi.lmu.de
>             <mailto:andreas.abel at ifi.lmu.de>>__wrote:
>
>                 +1 AMP
>                 +1 MINIMAL
>                 +1 Pointed in base
>
>
>     --
>     Andreas Abel  <><      Du bist der geliebte Mensch.
>
>     Theoretical Computer Science, University of Munich
>     Oettingenstr. 67, D-80538 Munich, GERMANY
>
>     andreas.abel at ifi.lmu.de <mailto:andreas.abel at ifi.lmu.de>
>     http://www2.tcs.ifi.lmu.de/~__abel/ <http://www2.tcs.ifi.lmu.de/~abel/>
>
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>


-- 
Andreas Abel  <><      Du bist der geliebte Mensch.

Theoretical Computer Science, University of Munich
Oettingenstr. 67, D-80538 Munich, GERMANY

andreas.abel at ifi.lmu.de
http://www2.tcs.ifi.lmu.de/~abel/