Re: [Caml-list] issue with polymorphism

[Yotam Barnoy <yotambarnoy@gmail.com>]

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Right, but they can't be inferred on objects and records either, and yet
they're allowed there... so what was the rationale?

On Mon, May 16, 2016 at 2:53 PM, Gregory Malecha <gmalecha@gmail.com> wrote:

> 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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