How do I design this?

design.fsx

/// My function types 
type Backward<'Core> = 'Core -> 'Core

type InputCore = {
  backward : Backward<InputCore>
  x : float
}

type TanhCore = {
  backward : Backward<TanhCore>
  y : float
}

type Layer =
  | Input of InputCore
  | Tanh of TanhCore

module Input =
  let backward c = // do some core specific computation
    { c with x = c.x * 3.423 }
module Tanh =
  let backward c = // do some core specific computation
    { c with x = c.y * c.y }
    
/// Now, having a list of varoius Layer type instances, I want to call the `backward` 
// function on every of them without matching on each.

let backward (lst:Layer list) =
    lst
    |> List.map (fun l -> 
        match l with 
        | Input core -> Input.backward core
        | Tanh core -> Tanh.backward core
  )