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From: dvdeug@x8b4e53cd.dhcp.okstate.edu (David Starner)
Subject: Re: Function name problem
Date: 2000/01/16
Message-ID: <85stib$a2g1@news.cis.okstate.edu>#1/1
X-Deja-AN: 573416347
References: 
 <B4A633AE.3FF3%Harald.Schmidt@tomcat.de><85qecu$24r$1@nnrp1.deja.com>
 <B4A76C00.4583%Harald.Schmidt@tomcat.de>
Organization: Oklahoma State University
User-Agent: slrn/0.9.6.2 (Linux)
Reply-To: dstarner98@aasaa.ofe.org
Newsgroups: comp.lang.ada
Date: 2000-01-16T00:00:00+00:00
List-Id: <comp.lang.ada>

On Sun, 16 Jan 2000 12:37:21 +0100, Harald Schmidt <Harald.Schmidt@tomcat.de> wrote:
>in article 85qecu$24r$1@nnrp1.deja.com, Jeff Carter at
>jrcarter001@my-deja.com wrote on 15.01.2000 19:30:
>
>> A function declaration with the function designator (name) in quotation
>> marks (such as "=") defines an operator. The set of operator symbols is
>> fixed in Ada. While you can define operators for your types, as you did
>> with "=", you cannot create new operator symbols, as you tried to do
>> with "==". See ARM 4.5, 6.1, and 6.6.
>
>Thank you very much for this info. But can someone
>explain why this restriction exists?

Because it's a pain to implement, and it rarely improves readability.

(1) Where do you put the new operator? Any fixed place will be wrong
much of the time, and a flexible place will kill the parsing speed,
cause much pain for parser writers, and make the program hard to read.
f := a % b && c == d; could have almost any precedence, and since 
builtin precedence is already enough of a readibility problem . . .

(2) What do you gain from it? "==" is an example of why not to have it;
Writing C in Ada is a sure way to annoy and confuse anyone else reading
it. If I could use Unicode in writing programs, I can see a few places
where mathematical symbols would make nice operators, but still, 
a {dot symbol} b and a {cross symbol} b aren't superior enough to
Dot(a,b) and Cross (a, b) to make the precidence and readibility
problems worth it.

I will also note that POP-11(?) and ML allow this, but most other modern
languages found it too much trouble. (Java doens't allow operator overloading,
the Modula 3 people probably found it took too many pages in the standard, etc.)To be vague, I'd like to point out that Stroustroup had a commentary on why not
for C++ somewhere - Design and Evolution of C++, maybe?

-- 
David Starner - dstarner98@aasaa.ofe.org
If you wish to strive for peace of soul then believe; 
if you wish to be a devotee of truth, then inquire.
   -- Friedrich Nietzsche