Re: Ideas for Ada 200X

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

Russ wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:<bcrpc1$mi00f$1@ID-77047.news.dfncis.de>...
>> That thing is called overloading. BTW, see my example below for a
>> procedure, which does *not* modify any of its arguments.
> 
> If i := i + 1 is equivalent to i + 1, then what does
> 
>     i = i + j + 1
> 
> mean?

It depends on the set of visible procedures and functions. However from the 
above it is absolutely unclear what you mean.

A. An expression: if i = i + j + 1 then ...

Then no procedure is even considered. A call to a procedure may appear in a 
call-statement only. (Sorry for a tautology (:-))

B. A statement, assuming that "=" should be ":=", plus a trailing semicolon:

i := i + j + 1;

Then everything left of ":=" is an expression, and see A.

C. If "=" is "=" and it is again a statement then things get more 
interesting:

i = i + j + 1;

The compiler should consider:

C.1  i = (i + j + 1);   -- "=" is a procedure 
C.2  (i = i) + (j + 1); -- 1st "+" is a procedure
C.3  (i = i + j) + 1;   -- 2nd "+" is a procedure

Because of operation priorities only C.1 is considered. So "=" is definitely 
a procedure, if exists, otherwise it is a compile error. Everything else 
are functions.

Technically it is no problem to parse that. Business as usuall for a 
compiler.

> Does j get incremented by 1? Either way, I'd say readability
> went out the window.

Well, overloading has problems with that. Yet, it is allowed in most of 
languages.

It is programmer's duty not to misuse overloading. Note that any additional 
operation reduces readability:

X := X + Y;
X +:= 1;

This could become a puzzle for a reader. Why author adds Y using a function 
but when he adds 1 he uses a procedure? Is there any semantic difference, 
or is it just a matter of taste? Could the code be improved when both were 
functions or procedures? May a change of implementation of "+" or "+:=" 
infuence the decision. Should we inspect the implementations? Should we 
revise all the code?

--
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de