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To: tim@fungible.com
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Recursion between class and value?
In-Reply-To: <20020818174932.712167F63@lobus.fungible.com>
References: <20020818174932.712167F63@lobus.fungible.com>
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Message-Id: <20020819110119P.garrigue@kurims.kyoto-u.ac.jp>
Date: Mon, 19 Aug 2002 11:01:19 +0900
From: Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp>
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From: tim@fungible.com (Tim Freeman)
> I'd like to be able to have a class and a function be mutually
> recursive, kind of like this:
> 
>    class foo = object
>      method bar x =
>        if x > 0 then baz (x - 1)
>        else ()
>    end
> 
>    let baz z =
>      if z > 0 then
>        (new foo)#bar (z - 1)
>      else ()

The recursion is between baz and the constructor of foo (not the
type). So this is only a value level problem.

While your solution is ok:
> The best I know how to do is transform baz into a method on foo,
> yielding this:

A simpler one is to make new foo a parameter of baz:

  let baz ~new_foo z = 
    if z > 0 then new_foo#bar (z - 1)

  class foo = object
    method bar x = if x > 0 then baz ~new_foo:(new foo) (x - 1)
  end

  let baz n = baz ~new_foo:(new foo) n

A little heavy, but pretty classical.
An even heavier approach, but maybe more intuitive, is to put baz in
another class, do that you can access foo's constructor.

Jacques Garrigue
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