Re: recursive types

[Remi Vanicat <vanicat@debian.org>]

"Jacques Le Normand" <rathereasy@gmail.com> writes:

> hello again list
> is it possible to have mutually recursive classes and types? I'm trying to
> implement the zipper, and this is what I came up with:

Not directly, but you can use polymorphism to have it:


class type ['a] node_wrapper =
object
  method identify : string
  method get_child_location : 'a
end

class virtual ['a] nodeable =
object(self)
  method virtual to_node_wrapper : 'a node_wrapper
end

type path = (location nodeable list * location * location nodeable list) option
and location = Loc of location nodeable * path

you could even do something like :


class type ['a] pre_node_wrapper =
object
  method identify : string
  method get_child_location : 'a
end

class virtual ['a] pre_nodeable =
object(self)
  method virtual to_node_wrapper : 'a pre_node_wrapper
end

type path = (location pre_nodeable list * location * location pre_nodeable list) option
and location = Loc of location pre_nodeable * path

class type node_wrapper = [location] pre_node_wrapper

class virtual nodeable = [location] pre_nodeable

(you could also make the type polymorphic, and the class
monomorphic if you declare the type before the class and class
type). 

You probably should come on the Beginner's list, where such question
could be answered (see http://groups.yahoo.com/group/ocaml_beginners)

--
Rémi Vanicat