Re: Problems with 'class, help anyone?

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> Robert A Duff wrote:
> 
> > "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> > 
> >> That's right, but there is a case where "function" really differs from
> >> "procedure". I mean protected objects. ...
> > 
> > That's *another* example of basing things on a kludge.
> > Certainly, it makes sense to distinguish read-only from read-write
> > locking.  But to base that on "function" vs "procedure" is ...
> > well, Yuck.
> 
> Absolutely
> 
> > Protected functions are *not* functions (in the maths sense),
> > and therefore should not be so called.
> 
> Well, strictly speaking "+" is also not the mathematical +. Who cares.

You mean because it can overflow?  And because (for floats), it can give
a "close-but-wrong" answer?

Or do you mean, because the user can redefine it to do something else,
including having side effects?

>... But I 
> agree that protected function is not the best name for the thing.
> 
> >>... "function" vs. "procedure" for a
> >> protected object could potentially mean different implementation and
> >> performance. So I think that one should leave "function"s as they are,
> >> and just allow procedures with results:
> >> 
> >>    procedure Foo (...) return Bar;
> > 
> > Yeah, and then eliminate the "function Foo..." syntax.
> > That would solve the problem!
> > 
> > Slight incompatibility...  ;-)
> 
> I am not afraid of! (:-))

I can assure you that if the ARG changed the syntax in this way,
they would be tarred and feathered (or at least ignored)!  ;-)

> But we still need some keywords for:
> 
> 1. Subroutine (=procedure)
> 2. Subroutine with no side-effects other than on the arguments (=?)
> 3. Subroutine with only one side-effect on the result (=?)

I think 2 and 3 should use the same syntax on the declaration.
To me, it's a minor point whether a subroutine returns results
via a "function result" vs out parameter(s).

I would advocate a notation at the call site that indicates
out-parameterness.

> "function" in Ada is sort of 1. dressed as 3. (:-()
> 
> {1,2,3} is multiplied to:
> 
> A. Subroutine with no queue
> B. Subroutine with a queue (entry)

I am not convinced that these need a syntactic distinction.

> Well together it makes 3x2=6 different variants!
> 
> And not to forget the "notation" axis:
> 
> i.   operational x+y
> ii.  prefix (subroutines of protected objects, tasks, attributes)

I don't much like the prefix notation.

> iii. functional A(x,y)
> iv.  aggregated (x,y,z) (should Ada have user-defined ones?)

I don't know about Ada, but if I were designing a language from scratch,
I think I would include user-defined aggregates.  Also, user-defined
semantics for various other notations, like literals, "in", indexing,
and maybe a few others.

I would not go so far as Lisp, where you can redefine the meaning of
'if' statements, and you can even redefine the lexical rules of the
language.

- Bob