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=-1.2 required=5.0 tests=BAYES_00,FROM_LOCAL_HEX,
	FROM_STARTS_WITH_NUMS autolearn=no autolearn_force=no version=3.4.4
X-Google-Thread: 103376,de7dd126d6737f3a
X-Google-NewGroupId: yes
X-Google-Attributes: gida07f3367d7,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news4.google.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: "Vinzent Hoefler" <0439279208b62c95f1880bf0f8776eeb@t-domaingrabbing.de>
Newsgroups: comp.lang.ada
Subject: Re: Callback in Ada
Date: Sat, 27 Nov 2010 11:46:40 +0100
Message-ID: <op.vmtr72q3lzeukk@jellix.jlfencey.com>
References: <8lc2d0Fb6jU1@mid.individual.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed; delsp=yes
Content-Transfer-Encoding: 7bit
X-Trace: individual.net D3b+JsaBa6SGHoAyIkwkBQ0oC++IUMro518T36Gem2EMgTS/wf
Cancel-Lock: sha1:bNS3Vfl6tf1PoSRBFNhoWoJ3nXY=
User-Agent: Opera Mail/10.63 (Win32)
Xref: g2news2.google.com comp.lang.ada:16647
Date: 2010-11-27T11:46:40+01:00
List-Id: <comp.lang.ada>

Georg Maubach wrote:

> today I learnt what a callback function is and also how it is used in
> Python. I have tested the following code which runs in Python:
>
> def apply_to (function, valueList):
[...]

> Values doubled: 2, 4, 6, 8, 10
> Values powered: 1, 4, 9, 16, 25
>
> How would I do that in Ada?

The important thing is the Callback type and the 'Access attribute for the
function which you like to call.

-- 8< --
with Ada.Text_IO;

procedure Callback is

     function Duplicate (Value : in Integer) return Integer is
     begin
        return Value * 2;
     end Duplicate;

     function Power (Value : in Integer) return Integer is
     begin
        return Value * Value;
     end Power;

     type Int_List is array (Positive range <>) of Integer;

     type Callback is access function (Value : in Integer) return Integer;

     procedure Apply_To (Operation : Callback; Values : Int_List) is
        R : Integer;
     begin
        for V in Values'Range
        loop
           R := Operation (Values (V));
           Ada.Text_IO.Put (Integer'Image (R));
        end loop;

        Ada.Text_IO.New_Line;
     end Apply_To;

     Value_List : constant Int_List := (1, 2, 3, 4, 5);

begin
     Apply_To (Duplicate'Access, Value_List);
     Apply_To (Power'Access,     Value_List);
end Callback;
-- 8< --

Vinzent.