let getTypeOf argument = match argument with
  | (Variable(_) | Anonymous) -> Any
  | Set(_) -> Set
  | Integer(_) -> Int
  | String(_) -> String
  | Identifier(_) -> Identifier;;


(* just need to verify the parameters, really. *)
let rec verifyPredArgs args =
  let verifyPredArg arg = match arg with Argument(ty, var) ->
    (let varType = getTypeOf var in
      (match ty with
        | "Set" -> (match varType with
          | (Any | Set) -> true
          | _ as errType -> false)
        | "Int" -> (match varType with
          | (Any | Int) -> true
          | _ as errType -> false)
        | "String" -> (match varType with
          | (Any | String) -> true
          | _ as errType -> false)
        | _ as errType -> (* error! *) false
      )
    )
  in
    match args with
      | SingleArgument(ar) -> verifyPredArg ar
      | AnotherArgument(ar, more) -> verifyPredArg ar ; verifyPredArgs more;;