From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (from majordomo@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id EAA12753; Tue, 15 Oct 2002 04:41:26 +0200 (MET DST)
X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f
Received: from nez-perce.inria.fr (nez-perce.inria.fr [192.93.2.78]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id EAA12760 for <caml-list@pauillac.inria.fr>; Tue, 15 Oct 2002 04:41:25 +0200 (MET DST)
Received: from plinky.bolt-action.com (node-d8e9cca3-sfo-onnet.worldcom.com [216.233.204.163])
	by nez-perce.inria.fr (8.11.1/8.11.1) with ESMTP id g9F2fLD16851
	for <caml-list@inria.fr>; Tue, 15 Oct 2002 04:41:24 +0200 (MET DST)
Received: from CHECKERATH (node-d8e9cca2-sfo-onnet.worldcom.com [216.233.204.162])
	by plinky.bolt-action.com (8.11.6/8.9.3) with SMTP id g9F3TAX26896
	for <caml-list@inria.fr>; Mon, 14 Oct 2002 20:29:10 -0700
Date: Mon, 14 Oct 2002 20:29:10 -0700
Message-Id: <200210150329.g9F3TAX26896@plinky.bolt-action.com>
From: Chris Hecker <checker@d6.com>
To: caml-list@inria.fr
Subject: [Caml-list] monomorphic restriction or typing/scanf bug?
Sender: owner-caml-list@pauillac.inria.fr
Precedence: bulk


The "scan" function in the code below works if it's at global scope,
but not if it's defined inside the test2 function.  Is this a bug or a
typing restriction?  I assume the latter (and that I could have boiled
this example to one of the ones in the FAQ?), but I don't understand
these kinds of polymorphism typing issues.

Chris


type t =
    Foo of int
  | Bar of int * int 

exception FB of t


(* works *)
let scan s (fmt : ('a, Scanf.Scanning.scanbuf, 'b) format) f =
  try
    raise (FB (Scanf.sscanf s fmt f))
  with
    End_of_file | Scanf.Scan_failure _ -> ()

let test () =
  let line = "Foo 1" in
  try
    scan line "Foo %d" (fun i -> Foo i);
    scan line "Bar %d %d" (fun i j -> Bar (i,j));
    failwith "bad line"
  with
    FB t -> t

(* doesn't work *)
let test2 () =
  let line = "Foo 1" in
  let scan s (fmt : ('a, Scanf.Scanning.scanbuf, 'b) format) f =
    try
      raise (FB (Scanf.sscanf s fmt f));
      ()
    with
      End_of_file | Scanf.Scan_failure _ -> ()
  in
  try
    scan line "Foo %d" (fun i -> Foo i);
    scan line "Bar %d %d" (fun i j -> Bar (i,j));
    failwith "bad line"
  with
    FB t -> t

-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners