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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Interesting article on ARG work
Date: Sat, 7 Apr 2018 17:59:58 +0200
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Xref: reader02.eternal-september.org comp.lang.ada:51382
Date: 2018-04-07T17:59:58+02:00
List-Id: <comp.lang.ada>

On 2018-04-07 17:27, Dan'l Miller wrote:
> On Saturday, April 7, 2018 at 5:11:35 AM UTC-5, Dmitry A. Kazakov wrote:
>> On 2018-04-07 04:25, Randy Brukardt wrote:
>>
>>> The biggest problem with a lexical solution (and the reason that Ichbiah
>>> hated them) is that it's trivial to accidentally create a program that is
>>> only legal in one mode or the other. One has to continually compile
>>> everything in each possible mode to ensure that there aren't silly syntax
>>> errors involved. A common mistake that I make all of the time is:
>>>
>>>       if Foo then
>>>              Bar;
>>>       else
>>> @        Internal_Error;
>>>       end if;
>>>
>>> With the conditional compilation off, the "Internal_Error" is commented out
>>> and the above isn't syntactically legal.
>>
>> Yes, this is important but I think this could be resolved, e.g. by
>> compiling conditionals into corresponding null-effect constructs.
> 
> Yeah, right.  This is an artificially contrived “problem” that is in fact not extant in reality.  Simply put the @ symbols in front of the •entire• construct to elide:  the entire else branch.
> 
>      if Foo then
>             Bar;
> @ else
> @        Internal_Error;
>      endif;
> 

"@ else"
"@        Internal_Error;"

Is not a valid sequence of statements. The point is that like with 
pragma, the conditional must be a syntactic entity, e.g. a sequence of 
statements, a Boolean-valued expression, a declaration, not just a 
sequence of characters.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de