Re: What would you like in Ada202X?

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Fri, 27 Apr 2012 09:56:36 -0400, Robert A Duff wrote:
>> In my language, every named thing must have a unique name.
>> It can also have an overloaded name.
>
> Is the name space same?

Yes.

>...One could have a separate name space for unique
> names.

I'm not sure what you mean.  Usually "separate name space"
implies distinguishing which name space you're referring
to via some syntactic means.  For example, Ada could have
a separate namespace for labels, because they can only
appear after "goto" and inside <<...>>.

Oops, I forgot about Label'Address.  Nix that.

> So the imaginary setup is:
>
> 1. X and inner X are unambiguous: not Clash (X, inner X)
> 2. X hides outer X: Clash (X, outer X)
> 3. outer X and inner X are ambiguous: Clash (outer X, inner X)

I'm not sure what you mean.  I'm suggesting (and, I think, Randy was) a
rule where everything is overloadable, and if you have two things called
X, neither hides the other.  This is the way use-visibility work in Ada,
but only for subprograms.  Single namespace.

The name resolution rules would need to be completely rewritten,
but the basic idea is that if you can't tell which X it is
(based on those rules), it's ambiguous and therefore illegal.

There's no need to prevent clashes.  If you say:

    X: constant Integer := 123;
    X: constant Integer := 456;

(both in the same scope) then all references to X would be
ambiguous.  So don't do that.

These rules would not be compatible, therefore they won't
happen, and I'm not seriously proposing them.

> This looks broken already. Ambiguity must be transitive:
>
>    Clash (X, outer X) and  Clash (outer X, inner X) => Clash (X, inner X)

I agree that ambiguity should be transitive, and never meant
to suggest otherwise.  That is, if you swap inner X and outer X,
it wouldn't change the ambiguity of complete contexts that
have visibility on both.

> If not transitive, that must be fixed even if backward incompatible.

Well, we know you don't care very much about compatibility,
but I assure you ARG would be tarred and feathered if we
threw compatibility concerns out the window.  And rightly so.
The Ada 9X team and the ARG already get grumbling about the
fairly modest incompatibilities that were introduced.

There are all sorts of improvements that could be made
to Ada (or any other language) if we didn't care about
compatibility.  But the end result would be a different
language, and should therefore have a different name.

>> Hiding is evil.
>
> Yes, sometimes handy. My pet idea is that instead of hiding the language
> should require to rename the offending outer entities.

I should have said "Implicit hiding is evil."  Or "Accidental hiding is
evil."  I wouldn't mind having a feature like "hide X, Y, Z;", which
explicitly makes everything with those names vanish.

But anyway we're not going to get rid of implicit hiding in Ada
-- way too incompatible.

- Bob