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

[Tobias Brandt]

Your class looks like Unfoldable from
Data.Collections<http://hackage.haskell.org/package/collections-api-1.0.0.0/docs/Data-Collections.html>.
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 <spam at scientician.net> 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,
>
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