From: Mathieu Barbin <mathieu.barbin@gmail.com>
To: Alain Frisch <alain@frisch.fr>
Cc: Gabriel Scherer <gabriel.scherer@gmail.com>, caml-list@inria.fr
Subject: Re: [Caml-list] GADT: question about inference
Date: Sat, 27 Jul 2013 20:29:33 -0400 [thread overview]
Message-ID: <CANXn40kJj_wzL2QCf1Tm9avBLaYCbiPyqQD8t=FDZVgh-KNsbA@mail.gmail.com> (raw)
In-Reply-To: <51F2E937.7000809@frisch.fr>
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Got it. I missed that somehow until now. Indeed using eta expansion to
enforce introducing variable-like constructors works well, and looks like a
very reasonable work around for the cases I have in mind.
Thank you very much for the relevant links and the quick answers.
2013/7/26 Alain Frisch <alain@frisch.fr>
> On 7/26/2013 10:27 PM, Gabriel Scherer wrote:
>
>> This is explained in the manual (emphasis mine)
>> http://caml.inria.fr/pub/docs/**manual-ocaml/manual021.html#**toc85<http://caml.inria.fr/pub/docs/manual-ocaml/manual021.html#toc85>
>>
>> The constraints associated to each constructor can be recovered through
>>> pattern-matching.
>>> Namely, **if the type of the scrutinee of a pattern-matching contains a
>>> locally abstract type**,
>>> this type can be refined according to the constructor used.
>>>
>>
>> The only types that can be refined by the type equalities introduced
>> by GADT are locally abstract types, the variable-like constructor "a"
>> introduced by the "(type a)" and "foo : type a . bar" syntaxes. Your
>> first two examples have no locally abstract type, only type members of
>> modules, so there was no GADT refinement happening.
>>
>
> A feature request related to allowing more kinds of types to be refined by
> GADT patterns (abstract types in the current environment, introduced by
> unpacking a module -- but the same would be useful for abstract types in a
> functor's argument):
>
> http://caml.inria.fr/mantis/**view.php?id=5713<http://caml.inria.fr/mantis/view.php?id=5713>
>
> -- Alain
>
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prev parent reply other threads:[~2013-07-28 0:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-26 17:15 Mathieu Barbin
2013-07-26 20:27 ` Gabriel Scherer
2013-07-26 21:25 ` Alain Frisch
2013-07-28 0:29 ` Mathieu Barbin [this message]
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