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Date: 9 Apr 93 22:33:40 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!howland.reston.ans.net!noc.n
ear.net!inmet!spock!stt@ucbvax.Berkeley.EDU  (Tucker Taft)
Subject: Re: Language lawyer needed
Message-ID: <1993Apr9.223340.26114@inmet.camb.inmet.com>
List-Id: <comp.lang.ada>

In article <1993Apr2.193753.22289@inmet.camb.inmet.com> 
 stt@spock.camb.inmet.com (Tucker Taft) writes:

>In article <1993Apr1.215753.3147@oracorp.com> 
>  davidg@oracorp.com (David Guaspari) writes:
>
>>Here's a question for language lawyers.
>
>Oh boy.
>
>>Consider the following pathological program:
>>
>>   procedure Q(x : integer) is  
>>   begin
>>     declare
>>       x : integer;   -- (1)
>>     begin
>>       Q(x => 0);     -- (2)
>>     end;
>>   end Q;
>>
>> . . .
>>  However, the declaration in (1) is not visible by selection at the
>>  point at which x occurs in (2).
>
>This statement is false.  

Oops; I misread David's original sentence -- it is in fact
true.  The declaration in (1) is not visible by selection preceding
the "=>" in (2).  (My misreading had replaced "the declaration in (1)"
with "the first declaration of x".)

The basic confusion illustrated by David's message
comes from the word "hide" which does *not* imply the 
earlier declaration is "invisible" 
but rather simply not *directly* visible (I guess it is 
"indirectly visible" ;-).  

On the other hand, "hide from *all* visibility" does 
mean the declaration is visible neither directly nor by selection.  
This more "obscure" (so to speak) kind of hiding only happens in a 
few cases (within a subprogram specification, and for implicit
declarations overridden by explicit declarations).
It is probably best to just ignore these obscure cases when
trying to build an "intuition" for what the word "hide" means
in Ada.  

(Perhaps a better word for "hide" might be the verb "obscure" ;-)

>>- David Guaspari
>>  davidg@oracorp.com
>
>S. Tucker Taft      stt@inmet.com
>Ada 9X Mapping/Revision Team
>Intermetrics, Inc.
>Cambridge, MA  02138

-S. T. Taft