Re: [Caml-list] a reckless proposal

[Miles Egan <miles@caddr.com>]

On Tue, Jul 24, 2001 at 12:44:52PM -0700, Brian Rogoff wrote:
> >  Objects seem to provide more struct-like
> > semantics, i.e. field names need only be unique within their class definition.
> > Using objects in place of records is a bit clumsy, however, because object
> > fields require accessors.  If the rules for object field access were changed,
> > however, objects would be just as convenient as records and less
> 
> No, they'd still be *much* less convenient than records, since you can't
> pattern match on objects. 

That's a big disadvantage, I agree.
 
> > This approach has, in my mind, two advantages:
> > 1. The object system becomes more generally useful.
> > 2. A confusing and non-orthogonal feature of ocaml is subsumed into
> >    another, more generally useful and flexible feature.
> 
> I understand this desire to unify features and remove non-orthogonalities, 
> but I don't like this proposal. I think it would be more interesting to
> have a language with more polymorphism in records, as well as some more 
> flexibility in modules. By enhancing those aspects of the language the 
> advantages of classes would be reduced. 

Overall I agree.  I wonder if the inria folks are interested in making changes
in this area or if they're focusing on other things at the moment?  I'll take a
look at the SML# stuff.
 
> Of course, if you're really into confusing, errr, unifying concepts, I
> suppose we could unify modules and records too? No joke, I think a few 
> language designs do this.

As much as unifying concepts, I'm interested in identifying the "false friends"
new programmers encounter in Ocaml.  Records are such "false friends" I believe.
They resemble, even in syntax, C structs and are used in some fairly similar
ways, but functionally  they are quite different.  I think this fact would be
more obvious and less confusing if they weren't so enticingly but superficially
familiar.  Object syntax and behavior, on the other hand, is very similar to
that found in more mainstream languages and causes less confusion, I think.

Modules are another of these "false friends", I think.  In most commonly-used
languages, a module is rougly equivalent to a compilation unit and corresponds
to a source file.  In these languages, a module is essentially a collection of
related types and functions.  Ocaml top-level modules are very analagous, but
"modules" in ML are actually a very different beast with as much in common with
C++ templates as java packages.  This convolution of function wasn't clear to me
until I'd been programming in Ocaml for a while and I still find it fairly
dissonant psychologically.  In this case, I might even advocate ADDING new
terminology to Ocaml and explicitly distinguishing compilation units from
parametric polymorphs.

-- 
miles

"We in the past evade X, where X is something which we believe to be a
lion, through the act of running." - swiftrain@geocities.com
-------------------
Bug reports: http://caml.inria.fr/bin/caml-bugs  FAQ: http://caml.inria.fr/FAQ/
To unsubscribe, mail caml-list-request@inria.fr  Archives: http://caml.inria.fr