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From: Eric Hughes <eric.eh9@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: User-defined type attributes
Date: Thu, 13 Mar 2008 20:55:27 -0700 (PDT)
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Date: 2008-03-13T20:55:27-07:00
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On Mar 13, 1:58 pm, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> In which sense function is static? If understand what you wrote, it simply
> means that the name "Callable" is static.

That's not what I meant.  Here's some sample notation, whose syntax is
merely illustrative.

    -- Declaration of an attribute
    generic
        task type T ;
    function T'Callable return boolean ;

    -- Declaration of a (static) implementation function
    generic
        task type T ;
    function Callable_Impl return access function( X : T ) return
boolean is static ;

    -- Binding of an implementation to an attribute
    generic
        task type T ;
        Obj : T ;
    for Obj'Callable use Callable_Impl.all( X => Obj ) ;

Regardless of whatever syntax is appropriate, one of the things that
makes me uncomfortable about attributes is that their definitions
don't have the same rigor of notation in their definitions as, say,
the standard libraries do.  In the spirit of separation compilation,
I'd like to see attribute definitions in specification packages, even
if their bodies exist solely within a compiler's implementation.


I wrote:
> Functions on a type are part of the tradition algebraic
> specification of a type.  Attributes on a type are part of the
> language environment inside of which a type specification is
> expressed.  These are very different.

"Dmitry A. Kazakov" <mail...@dmitry-kazakov.de> wrote:
> I don't see why this distinction is important.

I'm afraid I don't know how to argue this point briefly.  It's the
difference between language (in the proof theory sense) and
metalanguage.  I guess I've done too much formal logic too see this
distinction and its import as anything other than obvious.

Eric