From: Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>
To: ebreck@cs.cornell.edu
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] changing the type of records using "with"
Date: Thu, 13 Jul 2006 11:43:39 +0900 (JST) [thread overview]
Message-ID: <20060713.114339.07638100.garrigue@math.nagoya-u.ac.jp> (raw)
In-Reply-To: <C54E1B4E-FF0D-4B79-88CA-8088605DD721@cs.cornell.edu>
From: Eric Breck <ebreck@cs.cornell.edu>
> I noticed the following behavior of the typing system:
>
> # type 'a foo = {a: 'a; b: int};;
> type 'a foo = { a : 'a; b : int; }
> # let one = { a = (); b = 5};;
> val one : unit foo = {a = (); b = 5}
> # let two = {one with a = "Hello"};;
> val two : string foo = {a = "Hello"; b = 5}
>
> i.e. "{one with ... }" can have a different polymorphic type argument
> than "one" does. This has been handy for me on a couple of
> occasions, but is it a documented feature that I can count on working
> in future versions of ocaml, or is it a quirk of the current version?
This behaviour is intentional. My interpretation of the reference
manual is that {one with a = "Hello"} should be strictly equivalent to
{a = "Hello"; b = one.b}. As a result I would say that requiring two.a
and one.a to have the same type would depart from this specification.
Jacques Garrigue
prev parent reply other threads:[~2006-07-13 2:41 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-12 13:56 Eric Breck
2006-07-13 2:43 ` Jacques Garrigue [this message]
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