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From: ka@sorry.no.email (Kenneth Almquist)
Newsgroups: comp.lang.ada
Subject: Re: Certified C compilers for safety-critical embedded systems
Date: 8 Jan 2004 22:49:02 -0500
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Date: 2004-01-08T22:49:02-05:00
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Robert A Duff <bobduff@shell01.TheWorld.com> wrote:
> During the Ada 9X project, some folks suggested making [the random
> number generator subprogram be] a procedure.
> This was considered a non-starter, primarily because Fortran uses a
> function, and that's what people expect.  It is rather strange that
> (some of) the same language designers who choked at the idea of making
> Random a procedure were adamant about forbidding 'in out' params.

A quote about eating your own dog food comes to mind here...

It's not just expectations created by other languages which are a
problem here.  A few years ago I wrote a package which looked in
part like:

    package Buffered_IO is

       type Buffered_Input is tagged abstract limited private;

       -- A buffered input object reads data in large blocks for
       -- efficiency, similar to the C standard I/O library or the
       -- C++ "istream" type.  To read an input source, you first
       -- declare and initialize a type derived from Buffered_Input;
       -- The details of how you do this depend on where the data
       -- is coming from; see the child packages of Buffered_IO for
       -- details.  However, once an input source is opened, you can
       -- read it like you would expect:

       procedure Get(File : in out Buffered_Input'class;
                     Item : out Character);
       pragma inline(Get);
       procedure Get(File : in out Buffered_Input'class;
                     Item : out String);
       function End_Of_File(File : in out Buffered_Input'class)
                           return Boolean;

Oops, that last declaration is illegal.  But am I seriously going to
ask Ada programmers to write code like:

       loop
          End_Of_File(Input, EOF);
       exit when EOF;
          ...
       end loop;

I don't think so.  So I changed the paramter mode of End_Of_File to "in",
and used by GNAT to implement Ada.Numerics.Discrete_Random to allow the
parameter to be used like an "in out" parameter.
				Kenneth Almquist