Address an elemet from a list from Data.List.Linear

Is your feature request related to a problem? Please describe.

Data.List.Linear doesn't seem to provide a simple function akin to (!!) for the non-linear List. What would be the recommended way of doing it?

Describe the solution you'd like

This is a prototypical linearListElemAtM and linearListElemAt that allow one to address the element by providing a (monadic in the M-variant) function that duplicates the element.

linearListElemAtM :: forall a m.
  Control.Functor.Linear.Monad m =>
  (a ⊸ m (a, a)) -> [a] ⊸ Int -> m (Maybe a, [a])
linearListElemAtM dupM xs idx =
  let !(ys, zzs) = L.splitAt idx xs
  in case L.uncons zzs of
        Just (a, zs) -> dupM a Control.Functor.Linear.>>= \(a1, a2) ->
          Control.Functor.Linear.pure (Just a1, ys L.++ a2 : zs)
        Nothing      -> Control.Functor.Linear.pure (Nothing, ys)

linearListElemAt :: forall a.
  (a ⊸ (a, a)) -> [a] ⊸ Int -> (Maybe a, [a])
linearListElemAt dupF xs idx = L.runIdentity (linearListElemAtM (\x -> L.Identity (dupF x)) xs idx)

Describe alternatives you've considered

I have not found what's the "recommended" way for doing it.

Additional context

This prototype does assume Dupable instance for a, for Dupable instance a specialized function may be provide, instead.

Start by reading the Data.List.Linear API and its existing splitAt, uncons, and append operations. Compare the proposed linearListElemAtM and linearListElemAt signatures with the module's conventions, including how duplication is represented. Done means resolving the Dupable question and establishing the intended behavior for valid and out-of-range indices.