From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Interfaces.C questions
Date: Sun, 19 Mar 2017 23:53:01 +0000
Organization: A noiseless patient Spider
Message-ID: <lyziggddsy.fsf@pushface.org>
References: <ej31ppF6c01U1@mid.individual.net>
	<ej81i5F6f41U1@mid.individual.net> <ly4lypdqce.fsf@pushface.org>
	<ej85m3F79k3U1@mid.individual.net>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: mx02.eternal-september.org;
 posting-host="9d1255fe3bfd76f1b16fb83b93d1fcf5";
	logging-data="9264"; mail-complaints-to="abuse@eternal-september.org";
	posting-account="U2FsdGVkX19INADHrP1aZe9M089CShgsJ+SauUPSmxU="
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (darwin)
Cancel-Lock: sha1:KzZUhSO2qNH3rhiIdhMdvyvXRNI=
	sha1:OG5yeilReUU+d3lNRf7OfH1vpgM=
Xref: news.eternal-september.org comp.lang.ada:46428
Date: 2017-03-19T23:53:01+00:00
List-Id: <comp.lang.ada>

hreba <f_hreba@yahoo.com.br> writes:

> On 03/19/2017 08:22 PM, Simon Wright wrote:
>> hreba <f_hreba@yahoo.com.br> writes:
>>
>>>    function func (x: C.double; params: Void_Ptr) return C.double is
>>>    begin
>>>       return C.double (real_func (Real(x)));
>>>    end func;
>>>    pragma Convention (C, func);		-- this is line 37
>>
>> Try
>>
>>    function func (x: C.double; params: Void_Ptr) return C.double;
>>    pragma Convention (C, func);
>>    function func (x: C.double; params: Void_Ptr) return C.double is
>>    begin
>>       return C.double (real_func (Real(x)));
>>    end func;
>>
>> You have to have a spec, but there's nothing stopping it being declared
>> right before the body.
>>
>> Of course, in most cases you'd prefer to do that earlier.
>>
>
> Did that. Now I get:
>
> gsl.adb:35:26: pragma "CONVENTION" argument must be in same declarative part

This compiles for me (with a warning, 'variable "real_func" is read but
never assigned'):

generic
   type Real is digits <>;
   type Parameters is private;
package GSL with Elaborate_Body is
   type Real_Function is access function (x: Real) return Real;
end Gsl;
with Interfaces.C;
package body Gsl is

   use Interfaces;

   type Void_Ptr is access all Integer;
   pragma Convention (C, Void_Ptr);

   type GSL_Function is record
      func:   access
	function (x: C.double; params: Void_Ptr) return C.double;
      params: Void_Ptr;
   end record;
   pragma Convention (C, GSL_Function);

   real_func:	Real_Function;

   function func (x: C.double; params: Void_Ptr) return C.Double;
   pragma Convention (C, func);

   function func (x: C.double; params: Void_Ptr) return C.double is
   begin
      return C.double (real_func (Real(x)));
   end func;

   procedure P is
      gslf:	aliased GSL_Function;
   begin
      gslf.func:= func'Access;
   end P;
end Gsl;