Re: [Caml-list] Object Features

[Goswin von Brederlow <goswin-v-b@web.de>]

On Sun, Nov 30, 2014 at 02:45:19PM +0100, Philippe Wang wrote:
> Hi,
> 
> Just some quick thoughts about 3.: it's not object matching! It looks
> a little like it, but it's not at all, in the sense that it's not at
> all like the rest of OCaml's pattern matching stuff.
> I would somewhat find it useful, but probably too misleading and
> confusing to encourage having this feature.
> 
> I was going to say it's not shorter or easier to write it this way, but actually
>     let myFunction delta {<x; y; ..>} = x + y + delta
> is a little shorter than something like
>     let myFunction delta (o: <x:'a; y:'b; ..>) = o#x + o#y + delta
> but, still, I don't really see something good in there.
> 
> Cheers,
> Philippe Wang

How about this syntax (similar to local open of modules):

let myFunction delta o = o#(x + y + delta)

MfG
	Goswin

 
> On Sun, Nov 30, 2014 at 5:24 AM, Jordan W <jordojw@gmail.com> wrote:
> > Hello,
> >
> > I've encountered several situations where I would have benefited from the
> > following features. I am curious what some of the OCaml core developers
> > think about them.
> >
> > 1. Object punning:
> > I understand that object punning on "functional updates" to objects was
> > recently added to trunk. This is a nice consistency, but I haven't found a
> > way to perform object punning on methods or values for object *expressions*.
> >
> >     let x = 10
> >     let y = 20
> >     let o = object
> >       method x
> >       method y
> >     end
> >
> > Which would create an object with two methods x, y that return x and y
> > respectively. It may be easy to apply the same convention to object values.
> >
> > 2. Object extension: I believe that OCaml immediate objects are fairly
> > under-appreciated, and most people could find useful applications for them
> > (at least) in the form of row polymorphic records. However, there are
> > several features that would make them even more powerful. The feature I long
> > for the most is object extension (on immediate objects). OCaml has support
> > for extending objects (inheritance), but only via classes. I understand that
> > implementing this may complicate dynamic dispatch and/or use of `self`, but
> > perhaps some compromise could be reached - something like a limited form of
> > `inherit`, that is allowed to have different semantics and works on
> > immediate objects (at least in the case when objects are being used as
> > row-polymorphic records).
> >
> >     let oldObj = object method x = 20 method greet = "hi" end
> >     let newObj = {<oldObj with method x = 10 >}
> >
> > This is similar to Andreas Rossberg's Record Extensions in SuccessorML.
> >
> > New languages are picking up these extensible record features as described
> > in Daan Leijen's paper [Extensible Records With Scoped Labels] and I suspect
> > this feature will be of interest to many others.
> >
> > 3. Object matching.
> >
> >     let myFunction delta {<x; y; ..>} = x + y + delta
> >
> >     let myFunction delta o = match o with
> >         {<x; y; .. >} -> x + y + delta
> >
> >
> > This may be relatively easy to implement (my reasoning is that I believe it
> > could even be solved at the parsing stage (not that it would be a good idea
> > to do so)).
> >
> >
> > Thanks for listening. I'm curious if anyone's given thought to implementing
> > these, and eager to hear thoughts/suggestions.
> >
> > Jordan
> 
> -- 
> Caml-list mailing list.  Subscription management and archives:
> https://sympa.inria.fr/sympa/arc/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs