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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: relax double parens in expression_function_declaration?
Date: Mon, 20 Feb 2017 16:11:01 -0600
Organization: JSA Research & Innovation
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Date: 2017-02-20T16:11:01-06:00
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"Simon Wright" <simon@pushface.org> wrote in message 
news:lybmtwk1gd.fsf@pushface.org...
...
> Actually there is, I think, a typo: the first semicolon in
> http://www.ada-auth.org/standards/rm12_w_tc1/html/RM-6-8.html#p2 should
> be a pipe, '|'.

???. The declaration ends with a semicolon, and since the next line starts 
with a pipe, it's clearly not missing.

...
>> ARM 4.5.7(7) gives permission to remove the double parens for
>> conditional_expression; is there a similar rule or AI for aggregates?
>
> AARM 4.5.7(7.j),
> http://www.ada-auth.org/standards/aarm12_w_tc1/html/AA-4-5-7.html#p7.j,
> says
>
>   The English-language rule applies in all places that could surround
>   an expression with parentheses, including pragma arguments, type
>   conversion and qualified expression operands, and array index
>   expressions.
>
> but it's far from clear what that means, & if it applies to aggregates,
> why that couldn't have been made explicit in (7) in the first place!

That rule doesn't apply to aggregates; we have an explicit rule in 6.8 for 
the case of aggregates in expression functions. Double parens are required 
for aggregates in those other contexts (most of which don't allow aggregates 
anyway - they're illegal for other reasons), or, like qualified exprssions, 
they also have explicit rules allowing the aggregate without double parens.

Mainly what the 4.5.7(7) means is that we didn't want to hack the Ada 
grammar enough to explicitly eliminate the double parens. (It's not that 
hard to do -- I did it in the Janus/Ada grammar -- but it does require 
extensive grammar changes). So we just said that they don't happen for 
conditional expressions (and quantified expressions -- interestingly, 
raise_expressions are handled explicitly).

                                        Randy.