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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada.Execution_Time
Date: Tue, 14 Dec 2010 10:53:40 -0500
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Date: 2010-12-14T10:53:40-05:00
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"Vinzent Hoefler" <0439279208b62c95f1880bf0f8776eeb@t-domaingrabbing.de>
writes:

> I believe, back in the old days, there was a requirement that the presence or
> absence of a pragma shall have no effect on the legality of the program, wasn't
> it?

Yes, something like that.  It applied only to implementation-defined
pragmas, which smells fishy right there.

Anyway, it was a pretty silly rule.  So you can erase all the pragmas,
and your program is still legal.  But the program now does something
different (i.e. wrong) at run time.  How is this beneficial?

Try erasing all the pragmas Abort_Defer from your program!
Or for a language-defined one, try erasing all the pragmas
Elaborate_All.  Either way, your (still-legal) program
will be completely broken.

> Well, even if it just was that it "shall have no effect on a legal program", I
> still wonder why it is so necessary to introduce the possibility to turn an
> illegal program (without the null statement) into a legal one merely by adding
> some random pragma where a "sequence of statements" was expected.

People don't add "random" pragmas.  They add useful ones.

>...A pragma is
> /not/ a statement.

True, but a sequence_of_statements can contain pragmas.  Huh.
A pragma can act as a statement, but can't BE a statement.

> I agree with Georg here, this is an unnecessary change with no apparent use,
> it doesn't support neither of the three pillars of the Ada language "safety",
> "readability", or "maintainability".

It certainly supports readability.  I find this:

    if Debug_Mode then
        pragma Assert(Is_Good(X));
    end if;

slightly more readable than:

    if Debug_Mode then
        null;
        pragma Assert(Is_Good(X));
    end if;

- Bob