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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Reconsidering assignment
Date: Mon, 11 Jun 2007 13:57:59 -0500
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Date: 2007-06-11T13:57:59-05:00
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"Maciej Sobczak" <see.my.homepage@gmail.com> wrote in message
news:1181428673.148991.76570@p77g2000hsh.googlegroups.com...
...
> > which were ambiguous:
> >
> >    X : Integer := 1 + 1;
> >
> > is it Positive'(1)+Positive'(1) or Integer'(1)+Integer'(1)? You will
need
> > complex preference rules to resolve this mess.
>
> It's a compile-time expression with the value 2.
> Not very complex. ;-)

Sorry, Dmitry is right; you seem to have missed his point. In order for this
to be "a compile-time expression", you need complex preference rules in your
type system. (That is, that "compile-time expressions" are preferred over
types that would cause some other kind of expression.) Such rules tend to be
very problematic in practice; they often have very counter-intuitive results
in some cases. Ada has very few of them for this reason, and the ones it has
do not include cases like this one.

It takes extreme care to design a self-consistent type system, and without
that care, it is impossible to say much of use on the topic.

                                 Randy.