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 20:10:17 +1200 [thread overview]
Message-ID: <ad8cfe7e0609130110m3f6da7bbu89bda2d1566025b3@mail.gmail.com> (raw)
In-Reply-To: <Pine.LNX.4.61.0609130924310.29369@orvieto.tcs.ifi.lmu.de>
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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next prev parent reply other threads:[~2006-09-13 8:10 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 ` Jonathan Roewen [this message]
2006-09-13 9:48 ` [Caml-list] " Jonathan Roewen
2006-09-13 9:36 ` Pietro Abate
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