Re: Other Ada Standards (was Re: SIGada Conference)

["Robert I. Eachus" <rieachus@comcast.net>]

Robert A Duff wrote:

> I don't agree.  You could say that "use A.B.C;" in a context clause
> implies a subset of "with A;", "with A.B;", and "with A.B.C;" -- just
> the ones that happen to be library units.  Or, you could *require* that
> they be library units, or be nested within already-mentioned library
> units, if you think that makes the code more readable.  Either rule
> would work, and be easily implementable.

The problem is upward compatibility, and some fun for implementors.  The 
requirement you mention would not be upwardly compatible.  If "use 
A.B.C;" could mean "with A; with A.B; use A.B.C;" or "with A; use 
A.B.C;" or with A; with A.B; with A.B.C; use A.B.C;" or ...  things get 
real messy fast.  Note that even if the compiler can figure it out, the 
reader is going to be faced with the same challenge.

Allowing "with and use" in addition to current context clauses, and only 
if the name is meaningful according to the rules for with clauses seems 
so much simpler, and is easy on readers as well.  To me that makes the 
implicit with a non-starter.

> Unfortunately, you can't just say that "use A.B.C;" is equivalent to
> "with A.B.C; use A.B.C;", because A.B.C might not be a library unit.
> Suppose A.B is a library package containing a nested package C.
> Then "with A.B; use A.B.C;" is currently legal.  We can't say it's
> equivalent to "with A.B; with A.B.C; use A.B.C;", because that would
> be illegal, so the rule would be incompatible.

Yep.

However, did you follow the discussion of "use all A.B.C;"?  That would 
be like the with rule, meaning "use A; use A.B; use A.B.C;"  I don't 
know if I would use it much, but the parallel construction has a lot to 
recommend it.  Of course, if we add that use all, I'd love to also have 
use all Ada.*; or more likely use all Ada.Text_IO.*. ;-)

-- 
                                           Robert I. Eachus

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