From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,f712c3cc98e7f25
X-Google-Attributes: gid103376,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII
Path: 
 g2news1.google.com!news1.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!newsfeed00.sul.t-online.de!t-online.de!kanaga.switch.ch!switch.ch!news.rediris.es!not-for-mail
From: Manuel Collado <m.collado@fi.upm.es>
Newsgroups: comp.lang.ada
Subject: Re: not X'Length
Date: Fri, 16 May 2008 10:04:23 +0200
Organization: RedIRIS
Message-ID: <g0jf8d$71j$1@heraldo.rediris.es>
References: <482c0030$0$7542$9b4e6d93@newsspool1.arcor-online.net>
 	<954e4cd2-11a9-420b-85c4-7741c429e1b2@c65g2000hsa.googlegroups.com>
 	<482ca195$0$6788$9b4e6d93@newsspool2.arcor-online.net>
 <717bf87e-b8b6-4129-8051-7bd45cf2f7b2@a9g2000prl.googlegroups.com>
NNTP-Posting-Host: sri202.sri.fi.upm.es
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
X-Trace: heraldo.rediris.es 1210925134 7219 138.100.242.202 (16 May 2008
 08:05:34 GMT)
X-Complaints-To: jesus.heras@rediris.es
NNTP-Posting-Date: Fri, 16 May 2008 08:05:34 +0000 (UTC)
User-Agent: Thunderbird 2.0.0.12 (Windows/20080213)
In-Reply-To: 
 <717bf87e-b8b6-4129-8051-7bd45cf2f7b2@a9g2000prl.googlegroups.com>
Xref: g2news1.google.com comp.lang.ada:92
Date: 2008-05-16T10:04:23+02:00
List-Id: <comp.lang.ada>

Adam Beneschan escribi�:
> On May 15, 1:48 pm, Georg Bauhaus <see.reply...@maps.futureapps.de>
> wrote:
>> christoph.gr...@eurocopter.com wrote:
>>> From RM 4.4 follows that this is equivalent to

>>> if (not X'Length) in Positive then

>>> Now Universal_Integer (X'Length is of this type) has no operators, so
>>> it has to be converted to an appropriate type. This is Integer (or, to
>>> be very precise, the type of Integer) in this case. But then there is
>>> no "not" defined for this type. So the compiler is correct.

>> While the compilers are correct, on the programmer's part the
>> issue is not that easy to understand in general.
>> You have demonstrated why this is so. Hence my original
>> question about programmer expectations regarding improved
>> compiler's diagnostics in this case.
> 
> You may be right that a better diagnostic would help in this specific
> case.  But a programmer cannot expect a compiler to be a mind-reader.
> And a compiler writer can't really go through every possible weird
> combination of things to figure out what sorts of accidental trouble a
> programmer could get themselves into---there are just too many
> possibilities.  About all a compiler writer can do is respond to
> particular situations when they get noticed.

Perhaps the compiler could state how the expression is parsed, so the 
diagnostic message can be better understood:

    if not X'Length in Positive then
                    |
    >>> incompatible types: parsed as
    >>> if (not X'Length) in Positive then

Just my 2c.
-- 
Manuel Collado - http://lml.ls.fi.upm.es/~mcollado