| A record of components @f r -> g r@ may be applied to a record of @f@ to
-- get a record of @g@.
rapply
  :: Rec (Lift (->) f g) rs
  -> Rec f rs
  -> Rec g rs
rapply RNil RNil = RNil
ra
rapply
  :: Rec (Lift (->) f g) rs
  -> Rec f rs
  -> Rec g rs
rapply RNil RNil = RNil
rapply RNil RNil = RNil