Re: Anybody in US using ADA ? One silly idea..

[Richard Riehle <richard@adaworks.com>]

Hyman Rosen wrote:

> The advantage is that more efficient (smaller/faster) code
> can be generated from generics, if not in theory then certainly
> in practice. Programming languages are not just abstract
> constructs, they are means for generating sequences of native
> machine code to perform some task.

Bill Findlay posted some code earlier, that I revised slightly
to make a point in this conversation.   Here is another example
using generics.

with Ada.Text_IO;
with Ada.Integer_Text_IO;
with System;
use  Ada;
procedure Conditional_Instantiation is
  X : Character := ' ';
  type Large_Number is range System.Min_Int..System.Max_Int;
  Bound : Large_Number := Large_Number'Last;
begin
  loop
    Text_IO.Put("Enter a Character: ");
    Text_IO.Get(X);
    Text_IO.New_Line;
    if X in 'A'..'Z' or X in 'a'..'z' then
       Text_IO.Put("Enter a number: ");
       Integer_Text_IO.Get(Integer(Bound));
       declare
          type Number is new Large_Number range 1..Bound;
          package IIO is new Text_IO.Integer_IO(Num => Number);
       begin
          Text_IO.Put("Upper Bound - 1 = ");
          IIO.Put(Number'Last - 1);
          Text_IO.New_Line;
       end;
    else
       exit;
    end if;
  end loop;
end Conditional_Instantiation;

Note that the result of the IIO.Put statement will reflect the
value of one less than whatever has been selected for the
value of Bound in the type declaration.   This will only
work on derived types and subtypes, but that is good
enough for most kind of applications.

Richard Riehle