From: John Max Skaller <skaller@ozemail.com.au>
To: David Frese <dfrese@dfrese.de>
Cc: Caml-list <caml-list@inria.fr>
Subject: Re: [Caml-list] Recursive type and class
Date: Sat, 31 Aug 2002 13:25:43 +1000 [thread overview]
Message-ID: <3D703737.5030508@ozemail.com.au> (raw)
In-Reply-To: <1030710136.1831.11.camel@pc-6>
David Frese wrote:
> Hello folks,
>
> I have a problem with mixing a class and a type recursively. Written
> down directly, I want to have something like this:
>
> type atype = Obj of aclass | I of int
>
> class aclass = object
> val mutable field0 : atype = I 5
> end
>
> But this does not work, of course. Can anyone tell me, how this can be
> done?
You first declare a class *type* with a type parameter:
class type ['t] aclass_t' = object val mutable field0: 't end
Now you declare the recursion:
type atype = Obj of atype aclass_t' | I of int
and finally you make a typedef for the class:
type aclass_t = atype aclass
Well that's got the typing right, so now you can
provide an implementation:
class ['t] aclass init = object val mutable field0: atype = init end
Note that the init value had to be lifted out, so you need a monomorphic
function to instantiate the instance class:
let mkclass () = new aclass (I 5)
Finally, to check it works:
# Obj (mkclass ());;
- : atype = Obj <obj>
[You might be able to make this simpler using a constraint,
I've never quite figured them out :]
--
John Max Skaller, mailto:skaller@ozemail.com.au
snail:10/1 Toxteth Rd, Glebe, NSW 2037, Australia.
voice:61-2-9660-0850
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prev parent reply other threads:[~2002-08-31 3:25 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-08-30 12:22 David Frese
2002-08-31 3:25 ` John Max Skaller [this message]
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