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boundary=001a11492ebe448bb40532fa4be0 Subject: Re: [Caml-list] issue with polymorphism --001a11492ebe448bb40532fa4be0 Content-Type: text/plain; charset=UTF-8 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 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 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 >> 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 > --001a11492ebe448bb40532fa4be0 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Right, but they can't be inferred on objects and recor= ds either, and yet they're allowed there... so what was the rationale?<= div class=3D"gmail_extra">
On Mon, May 16, 20= 16 at 2:53 PM, Gregory Malecha <gmalecha@gmail.com> wrote:<= br>

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 reas= on why we disallow writing this type directly?

On Mon, May 16, 2016 at 1:32 PM, Gerd St= olpmann <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?"
> >=C2=A0 =C2=A0ht= tps://ocaml.org/learn/faq.html#Howtowriteafunctionwithpolymorphicarguments<= /a>
>
> this page explains how to do it with records or objects, but ends with= a
> mysterious "FIXME: a direct way now exists". Does anyone kno= w what this might
> refer to?

What you would need is

let print_both : ('a . 'a -> 'a) -> unit =3D ...

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=C2=A0 =C2=A0 gerd@gerd-stolpmann.de
My OCaml site:=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 http://www.camlcity.org<= br> Contact details:=C2=A0 =C2=A0 =C2=A0 =C2=A0 http://www.camlcity.= org/contact.html
Company homepage:=C2=A0 =C2=A0 =C2=A0 =C2=A0http://www.gerd-stolpmann.de=
------------------------------------------------------------


--

- gregory malecha
=C2=A0 gmalecha.git= hub.io


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