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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Interesting article on ARG work
Date: Mon, 9 Apr 2018 15:24:39 -0500
Organization: JSA Research & Innovation
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Xref: reader02.eternal-september.org comp.lang.ada:51423
Date: 2018-04-09T15:24:39-05:00
List-Id: <comp.lang.ada>

Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:pag4fd$pn4$1@gioia.aioe.org...
> On 2018-04-09 18:12, Niklas Holsti wrote:
>
>> For example, the text
>>
>>  if Foo then
>>  Bar;
>> @ else
>> @ Baz;
>>  end if;
>>
>> would be parsed in four ways, according to the four combinations of 
>> choices (enabled/disabled) for the two @ signs:
>
> [...]
>
> It is a trivial recursive-descent parser. "else" cannot follow "@", 
> because there is no statement starting with "else". Full stop.

Of course, that would very much emasulate the feature (probably 25% of the 
@-code in Janus/Ada is to remove various "elsif" and "else" cases). 
[Remember, we designed this code to work on very small memory hosts, so 
anything not critical to the operation of the compiler is removed. One 
reason that I don't use that any more in production code.]

Another common use that you wouldn't allow is to remove the exception 
handler from some code. (For Janus/Ada, the existence of an exception 
handler has a cost, so if it is not needed for production code, it is best 
completely eliminated.)

I think you could come up with a rule that would be less harmful to the 
feature than requiring full statements, especially for composite statements 
like if and case and blocks.

                   Randy.