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From: "Nick Roberts" <nickroberts@blueyonder.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: What evil would happen?
Date: Sat, 12 Jul 2003 05:31:45 +0100
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Date: 2003-07-12T05:31:45+01:00
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"chris.danx" <spamoff.danx@ntlworld.com> wrote in message
news:1LEPa.9034$nP.7178@newsfep4-winn.server.ntli.net...
> Wojtek Narczynski wrote:
> > Hello,
> >
> > What would happen if a procedure could return a value
> > like a function,
>
> Surely, it would be a function?

I think the idea is that the result returned by the procedure is written
into an implicit variable with a conventional name. Suppose the name is
'Result', then you might have something such as:

   procedure P(...) is
   begin
      ...
      return X*25.4;
   end;

and then:

   P(...);
   if Result > 200.0 then
      ...

Some languages which are typeless (and/or fully polymorphic) have this kind
of facility. Nearly all assembly languages essentially work this way (think
of registers). I think it is clear how badly suited it is to a strongly
typed language such as Ada.

Obviously you could simulate the effect by simply writing into a global
variable, e.g.:

   Result: Float;

   procedure P(...) is
   begin
      ...
      Result := X*25.4;
   end;

but this is not considered good programming style.

A situation in which it might make sense for Ada to permit a return
statement with an expression in a procedure body is for a procedure which
will be called from a foreign language (and so to which pragma Export
applies). The call in the foreign language may look like a procedure call,
but the language may require a value to be invisibly returned by the
procedure (e.g. indicating success or some kind of failure).

Regarding the parameter modes of functions, I think the main Ada Issue to
refer to is AI-323.

--
Nick Roberts
Jabber: debater@charente.de [ICQ: 159718630]