type PairDispatcher = PairDispatcher with
  static member inline ($) (PairDispatcher,        (a, b)) = fun f -> f a b
  static member inline ($) (PairDispatcher, struct (a, b)) = fun f -> f a b
  
let inline fst x = (PairDispatcher $ x) (fun a _ -> a)
let inline snd x = (PairDispatcher $ x) (fun _ b -> b)

let res1 = fst (1, 2)
let res2 = snd struct (1, 2)