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Deriving Via for several datatypes #201

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Icelandjack opened this issue Oct 15, 2020 · 1 comment

Icelandjack commented Oct 15, 2020

If free is accepting via there are quite a few instances that can be derived

data Free.Final.Alt f a = ..
  deriving (Semigroup, Monoid)
  via Data.Monoid.Alt (Free.Final.Alt f) a

data Free.Alt f a = ..
  deriving (Semigroup, Monoid)
  via Data.Monoid.Alt (Free.Final.Alt f) a

  deriving (Functor, Applicative, Alternative)
  via Compose [] (AltF f)

newtype Trans.Free.ApT f g a = ..
 deriving (Functor, Applicative, Alternative)
 via Compose g (Trans.Free.ApF f g)

In any case I'm curious if there is any way we can derive the Free instances that isn't completely trivial.

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Author

Icelandjack commented Oct 15, 2020

Oh I guess Functor is attainable with this completely useless derivation

newtype F f a = F { runF :: forall r. (a -> r) -> (f r -> r) -> r }
 deriving Functor
 via Ran Identity (Monster f)

newtype Monster f r = Monster ((f r -> r) -> r)

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