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Date: -- (:)
From: Jonathan Roewen <jonathan.roewen@g...>
Subject: Re: [Caml-list] Modules within classes
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)
> >
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>