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

Bardur Arantsson spam at scientician.net
Mon Apr 21 05:09:13 UTC 2014

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.)


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