Re: Callback in Ada

["Vinzent Hoefler" <0439279208b62c95f1880bf0f8776eeb@t-domaingrabbing.de>]

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.