From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <Maxence.Guesdon@inria.fr>
X-Original-To: caml-list@sympa.inria.fr
Delivered-To: caml-list@sympa.inria.fr
Received: from mail3-relais-sop.national.inria.fr (mail3-relais-sop.national.inria.fr [192.134.164.104])
	by sympa.inria.fr (Postfix) with ESMTPS id 9316C7FBFF
	for <caml-list@sympa.inria.fr>; Fri, 23 Jan 2015 15:43:37 +0100 (CET)
X-IronPort-AV: E=Sophos;i="5.09,454,1418079600"; 
   d="scan'208";a="97481006"
Received: from adijon-652-1-166-140.w90-56.abo.wanadoo.fr (HELO alcazar2) ([90.56.101.140])
  by mail3-relais-sop.national.inria.fr with ESMTP/TLS/DHE-RSA-AES128-SHA; 23 Jan 2015 15:43:24 +0100
Date: Fri, 23 Jan 2015 15:43:23 +0100
From: Maxence Guesdon <Maxence.Guesdon@inria.fr>
To: caml-list@inria.fr
Message-ID: <20150123154323.1fc8e7d8@alcazar2>
Organization: INRIA
X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.23; x86_64-pc-linux-gnu)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Subject: [Caml-list] Strange type inference error

Hello,

I encountered a strange typing problem and reduced it to the following
code example:

====[t.ml]====
let mk_env () = None
let list_of_string (s: string) = [s]

let apply : 'a -> 'a option -> string list -> 'a * string list =
  fun acc env l -> (acc, ["hello"])

let f =
   let tmpl = ["coucou"] in
    fun ?(env=mk_env()) ->
      fun ~x ->
        fun () -> apply () env tmpl

let g =
   let tmpl = list_of_string "coucou" in
    fun ?(env=mk_env()) ->
      fun ~x ->
        fun () -> apply () env tmpl
====
Note that f and g only differ on the way tmpl is defined.

When I compile this file with ocaml 4.02.1, I get the following error:
File "t.ml", line 14, characters 3-119:
Error: The type of this expression,
       ?env:unit option -> x:'_a -> unit -> unit * string list,
       contains type variables that cannot be generalized

Am I missing something or should I file a bug report ?

Regards,

Maxence