From: "Jonathan Roewen" <jonathan.roewen@gmail.com>
To: "Martin Hofmann" <mhofmann@tcs.ifi.lmu.de>
Cc: caml-list@inria.fr, Oliver.Friedmann@web.de
Subject: Re: [Caml-list] Modules within classes
Date: Wed, 13 Sep 2006 21:48:37 +1200 [thread overview]
Message-ID: <ad8cfe7e0609130248r7acbbea8q36e0fe8e5284e99@mail.gmail.com> (raw)
In-Reply-To: <ad8cfe7e0609130110m3f6da7bbu89bda2d1566025b3@mail.gmail.com>
As for a workaround, use List.sort. I presume there's a real reason to
want to use Set rather than the contrived example given though... if
not, then there's your solution (=
Jonathan
PS: The order of traversing the list doesn't seem to be of much
significance, so List.fold_left might be better suited.
On 9/13/06, Jonathan Roewen <jonathan.roewen@gmail.com> wrote:
> It's the same at normal scope:
>
> type t = 'a;; doesn't compile.
>
> you need: type 'a t = 'a, which isn't compatible with input type for Set.
>
> I think the Set module is intentionally monomorphic...
>
> Jonathan
>
> On 9/13/06, Martin Hofmann <mhofmann@tcs.ifi.lmu.de> wrote:
> > Dear all,
> >
> > Can someone explain what is wrong here and perhaps suggest a workaround?
> >
> > class ['a] test ( l : 'a list) =
> > object
> > method result =
> > let module M =
> > struct
> > type t = 'a
> > let compare x y =
> > if x < y then -1 else if x > y then 1 else 0
> > end
> > in
> > let module MSet = Set.Make(M)
> > in MSet.elements (List.fold_right MSet.add l MSet.empty)
> > end;;
> >
> > OCaml says: "Unbound type parameter 'a".
> >
> > Our aim is of course not to program sorting the umpteenth time but to
> > have a means for using Pervasives.Set within a parametrised class.
> >
> > The problem seems to be that although "class ['a]" binds 'a its use is
> > nevertheless disallowed in the scope of the class declaration.
> >
> > Many thanks in advance!
> >
> > Martin Hofmann (on behalf of Oliver Friedmann)
> >
> > _______________________________________________
> > Caml-list mailing list. Subscription management:
> > http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list
> > Archives: http://caml.inria.fr
> > Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> > Bug reports: http://caml.inria.fr/bin/caml-bugs
> >
>
next prev parent reply other threads:[~2006-09-13 9:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-13 7:44 Martin Hofmann
2006-09-13 8:10 ` [Caml-list] " Jonathan Roewen
2006-09-13 9:48 ` Jonathan Roewen [this message]
2006-09-13 9:36 ` Pietro Abate
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