Levity polymorphic codensity

ekmett / kan-extensions

Kan extensions, Kan lifts, the Yoneda lemma, and (co)monads generated by a functor

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Closed Icelandjack closed 6 years ago

Icelandjack commented 6 years ago

I doubt this will get accepted, but it's worth noting that Codensity (and similar data types) can be made levity polymorphic

newtype Codensity (m::TYPE rep -> Type) a = Codensity
  { runCodensity :: forall b. (a -> m b) -> m b
  }

If it's worth adding I'll make PR, if I understand correctly it can even be given a kind?

Codensity :: (TYPE rep -> TYPE rep') -> (TYPE rep'' -> Type)

RyanGlScott commented 6 years ago