From: Brian Rogoff <bpr@best.com>
To: caml-list@inria.fr
Subject: RE: first class, recursive, mixin modules (was: RE: first class m odules)
Date: Sun, 14 Jan 2001 12:51:21 -0800 (PST) [thread overview]
Message-ID: <Pine.BSF.4.21.0101141249270.2654-100000@shell5.ba.best.com> (raw)
On Fri, 12 Jan 2001, Claudio Russo wrote:
> I wasn't quite sure of your intention, but I did get the attached code
> to work in Mosml (it includes a port of the Ocaml libraries and a
> fleshed out implementation of your idea).
Cool! OK, now Alain has at least one example of a practically useful case
handled by your scheme :-). I suspect that this problem bites lots of ML
programmers, and a fix is eagerly desired by at least two OCaml
programmers. Congratulations on making this work, the millenium is
starting off on a great note already!
> Unfortunately, this only works in an internal release of Moscow, because
> of a (known) bug in the current distribution.
Well, even more unfortunately, a fix in Mosml doesn't help me unless you
change to Mosocaml. I couldn't switch to SML even if I wanted to, and I
don't want to! Hopefully the OCaml Implementors (you guys are even
capitalized now) will "borrow back" the Mosml improvements into OCaml.
> For the record, your functor application Make(Ord)is fine because it is
> applied to a local, already defined structure.
[...snip...]
> An application like Make(T.Ord), through the forward reference, would
> raise the Bind exception, because T (and T.Ord) is
> undefined at that point (although Ord is).
That's no problem for me. Dave, in the case you mentioned, do you think
this would this be problematic? I couldn't guess from your description.
-- Brian
> > -----Original Message-----
> > From: Brian Rogoff [mailto:bpr@best.com]
> > Sent: 11 January 2001 20:01
> > To: Dave Berry
> > Cc: Claudio Russo; Alain Frisch; Caml list
> > Subject: RE: first class, recursive, mixin modules (was: RE:
> > first class
> > m odules)
> >
> >
> > My "litmus test" for recursive modules is that it fixes the well known
> > problem with expressing what OO folk call the Composite pattern,
> > essentially a recursively defined collection type with a leaf/node
> > relationship. Here is an approxmation of what I want to do in
> > "faux-Mosml
> > with OCaml libraries". Forgive my errors, I don't use SML. The idea
> > should be clear.
> >
> > signature COMPOSITE =
> > rec(X : sig structure CompositeSet : sig type t end end)
> > sig structure Composite :
> > sig
> > datatype t =
> > { data : int ; children : X.CompositeSet.t }
> > end
> > structure CompositeSet : (Set.S where type elt = Composite.t)
> > end;
> >
> > structure T = rec(X : COMPOSITE)
> > struct
> > structure Composite =
> > struct
> > datatype t = { data : int ; children : X.CompositeSet.t }
> > end
> > structure Ord : Set.OrderedType =
> > struct
> > type t = Composite.t
> > let compare = Pervasives.compare
> > end
> > structure CompositeSet = Set.Make(Ord)
> > end
> >
> > This is syntactically heavy, but better than the
> > parameterization trick
> > needed now, and I'd be satisfied. I do need to do that functor
> > instantiation, so if you can't do it in Mosml it needs to be added.
> >
> > I agree that the first-class module extension is useful on
> > its own too,
> > but in my own programming the problem I mention above arises
> > frequently
> > enough that I consider this a flaw of (current) ML style
> > modules. Every
> > language has flaws but since OCaml is so close to perfection
> > every flaw
> > seems large ;-).
> >
> > -- Brian
next reply other threads:[~2001-01-14 20:53 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-01-14 20:51 Brian Rogoff [this message]
-- strict thread matches above, loose matches on Subject: below --
2001-02-09 9:41 Claudio Russo
2001-02-09 16:47 ` Brian Rogoff
2001-02-09 21:45 ` William Chesters
2001-01-15 14:13 Dave Berry
2001-01-12 12:12 Claudio Russo
2001-01-11 18:15 Dave Berry
2001-01-11 20:01 ` Brian Rogoff
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