Re: [Haskell-cafe] Does this typeclass have a name?

Oh, and bar = mempty On 21 April 2014 15:46, Andras Slemmer <0slemi0@gmail.com> wrote:

I think what you're looking for are monoid actions: http://hackage.haskell.org/package/monoid-extras-0.2.2.0/docs/Data-Monoid-Ac... And the laws the typeclass should satisfy: foo bar = id foo f . foo g = foo (f `mappend` g)

The identity law is optional, in whihc case your 'e' would be a semigroup without a default 'bar'

On 21 April 2014 11:46, Tobias Brandt wrote:

...

Your class looks like Unfoldable from Data.Collectionshttp://hackage.haskell.org/package/collections-api-1.0.0.0/docs/Data-Collect.... foo is insert and bar is empty. The other three methods can be defined in terms of insert and empty.

On 21 April 2014 07:09, Bardur Arantsson wrote:

...

Hi all,

I was wondering if anyone out there knows if this type class has a name?

class Foo a e where foo :: e -> a -> a bar :: a

(I also have a fundep a -> e, but that's not essential.)

Essentially the usage is:

You have a sequence of "events" e_i and a starting value "bar" and can use the "foo" function to apply all events to that starting value

foo e_n $ foo e_{n-1} $ ... $ foo e_0 $ bar

and thus get the final value of the a induced by the events e_i.

(I've included the "bar" starting value in the type class, but I suppose it could be supplied by a Default instance.)

Regards,

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe