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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: choice_expression
Date: Mon, 8 Oct 2012 20:07:20 +0200
Organization: cbb software GmbH
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Date: 2012-10-08T20:07:20+02:00
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On Mon, 8 Oct 2012 10:01:46 -0700 (PDT), Adam Beneschan wrote:

> But
> here's a case (no less obscure than the examples you're providing) that
> isn't obvious:
> 
>    A and B in SOMETHING
> 
> where A and B are Booleans and SOMETHING is a subtype of Boolean or
> something like Array'Range where the array index type is Boolean.  Is this 
> 
>    (A and B) in SOMETHING
> 
> or
> 
>    A and (B in SOMETHING) ?

   not A in B

may mean either

   (not A) in B

 or

   not (A in B)  -- I think this is what Ada syntax does

Lattice operations are ambiguous. In mathematics they use different
notation for the operations Ada conflates. E.g. logical V vs. union U (like
in modular types). Both are denoted as "or" in Ada. It also uses | for U in
other cases. The membership test is conflated with the subset test and with
the subsumption test. All are just "in."

This might impose problems once ranges and tests become proper operations.

> But it's incorrect to say that Ada 83 avoided the problem of users having
> to guess precedence.

Ada found a way to solve the problem.

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