From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mail1-relais-roc.national.inria.fr (mail1-relais-roc.national.inria.fr [192.134.164.82])
	by walapai.inria.fr (8.13.6/8.13.6) with ESMTP id q2N4wO4n008909
	for <caml-list@sympa-roc.inria.fr>; Fri, 23 Mar 2012 05:58:24 +0100
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: ArkCAFYCbE9CbwQZk2dsb2JhbABEt08iAQEBAQkJCwkUBCOCNxECBjp0KYg9pRySbQaNYYI/Y4hajQgBky8
X-IronPort-AV: E=Sophos;i="4.73,633,1325458800"; 
   d="scan'208";a="150825182"
Received: from out1-smtp.messagingengine.com ([66.111.4.25])
  by mail1-smtp-roc.national.inria.fr with ESMTP/TLS/ADH-AES256-SHA; 23 Mar 2012 05:58:22 +0100
Received: from compute4.internal (compute4.nyi.mail.srv.osa [10.202.2.44])
	by gateway1.nyi.mail.srv.osa (Postfix) with ESMTP id C592020DCF
	for <caml-list@inria.fr>; Fri, 23 Mar 2012 00:58:20 -0400 (EDT)
Received: from frontend2.nyi.mail.srv.osa ([10.202.2.161])
  by compute4.internal (MEProxy); Fri, 23 Mar 2012 00:58:20 -0400
DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d=
	messagingengine.com; h=date:from:to:subject:message-id
	:mime-version:content-type; s=smtpout; bh=XbfKhZowvOMLlr0+TKJbzA
	aoe8g=; b=VU19YLI2nsu4teSa0vmRDl+xPE5ZKhCO1J0XGqWpyv+lvQXI2eU9Oz
	F77H8MkMrylbUupAdEPyFonlQo7TJnrzcB+jq8scyUq86TI2W5gywWMwH7o/PPAD
	LEdjTsO6IpTFbNbxfNCGfGtO/S6jbJqANx0nYqc0gokdi0MAq/TeI=
X-Sasl-enc: GV3kT3+OCvuiodWfJn563LGftTvZmwM7U5BankgN2tfM 1332478700
Received: from davidb.org (dweb.davidb.org [173.255.246.16])
	by mail.messagingengine.com (Postfix) with ESMTPSA id 6E3074825F9
	for <caml-list@inria.fr>; Fri, 23 Mar 2012 00:58:20 -0400 (EDT)
Date: Thu, 22 Mar 2012 21:58:18 -0700
From: David Brown <caml@davidb.org>
To: caml-list@inria.fr
Message-ID: <20120323045817.GA26450@davidb.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Disposition: inline
User-Agent: Mutt/1.5.21 (2010-09-15)
Subject: [Caml-list] Insufficient polymorphism in local let.

I'm trying to figure out how to get 'lmust' in 'get2' in the code
below to work.  It seems that it's type is being inferred as

   string -> string option -> string

instead of

   string -> 'a option -> 'a

The 'must' definition keeps it's polymorphism, as seen in 'get1'.  Is
there some way I can annotate the definition of 'lmust' so that it
will work?  Lifting 'lmust' out of 'get2' doesn't seem to help.

Thanks,
David

let must section name = function
   | Some o -> o
   | None -> 
     Printf.eprintf "Expecting %s in %s\n%!" name section;
     exit 1

type foo = { a: string; b: int }

let get1 a b =
   { a = must "get1" "a" a;
     b = must "get1" "b" b }

let get2 a b =
   (* This isn't polymorphic enough. *)
   let lmust = must "get2" in
   { a = lmust "a" a;
     b = lmust "b" b }