From: Arnaud Spiwack <Arnaud.Spiwack@lix.polytechnique.fr>
To: Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>
Cc: Philippe Veber <philippe.veber@gmail.com>,
caml users <caml-list@inria.fr>
Subject: Re: [Caml-list] Narrowing a signature with a constrained type
Date: Mon, 29 Jul 2013 10:51:49 +0200 [thread overview]
Message-ID: <CAMoPVjeACBSQZgRpPHX94V2wvMRYRqZH-Xs0xsLsbKYgvk3M0A@mail.gmail.com> (raw)
In-Reply-To: <059C2901-8AFE-4E28-B1D2-BC1D660CCA3A@math.nagoya-u.ac.jp>
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>
> Well, to ensure the coherence of the with constraints, we require that
> the new signature be a subtype of the original one (as a module, not as an
> object).
> This is where your code gets rejected.
>
> Now why is it deemed unsafe to allow a constrained type definition to be a
> subtype of
> an unconstrained one?
> Actually, I don't know.
> The unconstrained type does not enforce the invariants of the constrained
> one,
> but they will be checked as soon as you try to unify the two.
> So it may be possible to lift this restriction.
>
It sounds pretty unlikely. If I have a functor taking a T in argument and I
pass it a T with constraints, it's likely to be inconsistent.
May I wonder, though, about the reason why T with blah should be a subtype
of T? I must confess I fail to see the point.
Arnaud
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prev parent reply other threads:[~2013-07-29 8:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-26 13:32 Philippe Veber
2013-07-26 23:35 ` Jacques Garrigue
2013-07-27 20:07 ` Philippe Veber
2013-07-29 8:51 ` Arnaud Spiwack [this message]
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