No support for labelled parameters

[vch9]

I don't think we can reproduce the following behaviors with labelled parameters:

let rec spec_to_scenario :
    type fn r. rand:Random.State.t -> (fn, r) Spec.t -> fn -> (fn, r) t =
 fun ~rand spec f ->
  match spec with
  | Arrow ({ gen; _ }, Result _) -> (
      let x = Gen.generate1 ~rand gen in
      try
        let f = f x in
        Cons (x, Res (Ok f))
      with e -> Cons (x, Res (Error (Printexc.to_string e))))
  | Arrow ({ gen; _ }, spec) ->
      let x = Gen.generate1 ~rand gen in
      let f = f x in
      Cons (x, spec_to_scenario ~rand spec f)
  | Result _ -> Res (Ok f)

The only solution we currently have is to write:

let f ~x ~y = x + y

let test =
  let open Osnap in
  let small_int =
    Spec.
      {
        gen = QCheck.Gen.small_int;
        printer = Some string_of_int;
        encoding = None;
      }
  in
  let spec = Spec.(small_int ^> small_int ^>> Result.int) in
  let path = ".osnap/exponentiation" in

  Test.make ~spec ~path ~count:5 ~name:"exponentiation" (fun x y -> f ~x ~y)