From: Gregory Malecha <gmalecha@gmail.com>
To: Yotam Barnoy <yotambarnoy@gmail.com>,
Gerd Stolpmann <info@gerd-stolpmann.de>
Cc: Guillaume Hennequin <g.hennequin@eng.cam.ac.uk>,
caml users <caml-list@inria.fr>
Subject: Re: [Caml-list] issue with polymorphism
Date: Mon, 16 May 2016 18:53:14 +0000 [thread overview]
Message-ID: <CAGraiHJub80jTb-SPpKeT+iR5b93g5Q8vQ=qoi5benS_Uj7uyQ@mail.gmail.com> (raw)
In-Reply-To: <CAN6ygOmuzabSShsyO0WEUy8qtRj-UWs_1XTa6n-48KwX6JZF_w@mail.gmail.com>
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There may other reasons as well, e.g. performance and compilability, but
the main reason that I know is that inferring these types is difficult
(undecideable in general). For a point of comparison, GHC supports types
like this, but only when they are explicitly written.
On Mon, May 16, 2016, 11:50 AM Yotam Barnoy <yotambarnoy@gmail.com> wrote:
> Paging the type experts -- is there a concrete reason why we disallow
> writing this type directly?
>
> On Mon, May 16, 2016 at 1:32 PM, Gerd Stolpmann <info@gerd-stolpmann.de>
> wrote:
>
>> Am Montag, den 16.05.2016, 17:55 +0100 schrieb Guillaume Hennequin:
>> > Thanks all for your prompt answers;
>> >
>> > > See the FAQ entry, "How to write a function with polymorphic
>> arguments?"
>> > >
>> https://ocaml.org/learn/faq.html#Howtowriteafunctionwithpolymorphicarguments
>> >
>> > this page explains how to do it with records or objects, but ends with a
>> > mysterious "FIXME: a direct way now exists". Does anyone know what this
>> might
>> > refer to?
>>
>> What you would need is
>>
>> let print_both : ('a . 'a -> 'a) -> unit = ...
>>
>> i.e. the scope of the quantifier is restricted to the first argument.
>> This doesn't exist to my knowledge. Maybe it was part of some dev
>> version?
>>
>> Gerd
>> --
>> ------------------------------------------------------------
>> Gerd Stolpmann, Darmstadt, Germany gerd@gerd-stolpmann.de
>> My OCaml site: http://www.camlcity.org
>> Contact details: http://www.camlcity.org/contact.html
>> Company homepage: http://www.gerd-stolpmann.de
>> ------------------------------------------------------------
>>
>>
> --
- gregory malecha
gmalecha.github.io
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next prev parent reply other threads:[~2016-05-16 18:53 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-16 15:45 Guillaume Hennequin
2016-05-16 15:57 ` Gabriel Scherer
2016-05-16 16:55 ` Guillaume Hennequin
2016-05-16 17:32 ` Gerd Stolpmann
2016-05-16 18:49 ` Yotam Barnoy
2016-05-16 18:53 ` Gregory Malecha [this message]
2016-05-16 19:04 ` Yotam Barnoy
2016-05-16 19:09 ` Gregory Malecha
2016-05-16 15:57 ` Nicolas Ojeda Bar
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