Re: Language Lawyer question

[Keith Thompson <kst@cts.com>]

"David C. Hoos, Sr." <david.c.hoos.sr@ada95.com> writes:
> Wes Groleau <wwgrol@ftw.rsc.raytheon.com> wrote in message
> news:39380CEB.2CC4682E@ftw.rsc.raytheon.com...
> > One of my coworkers just asked an interesting question:
> >
> >    Why do we have to write
> >       Some_Type'Pred (Some_Value)
> >    when
> >       Some_Value'Pred
> >    is more natural/intuitive and
> >    carries just as much type info?

The grammar for an attribute reference is
     attribute_reference ::= prefix'attribute_designator
where
     prefix ::= name | implicit_dereference

Of course, that doesn't really answer the question; the grammar could
have been defined to allow an arbitrary expression as a prefix.  I
suppose it was defined that way for the sake of clarity, to prevent
expressions from becoming overly complex.

> What is 0'Pred?

If it were legal, it should be the same as 0 - 1 -- which means the
resolution would depend on the context.  (Note that the equivalence
between Foo'Pred and Foo - 1 wouldn't apply to enumeration types.)

> But, how would you do the equivalent of Modular_Type'Pred (0)
> with your syntax?

(Modular_Type'(0))'Pred

-- 
Keith Thompson (The_Other_Keith) kst@cts.com  <http://www.ghoti.net/~kst>
San Diego Supercomputer Center           <*>  <http://www.sdsc.edu/~kst>
Welcome to the last year of the 20th century.