Re: [Caml-list] [ANN] New release of visitors

[Gabriel Scherer <gabriel.scherer@gmail.com>]

This use of the monoid structure is very nice. I believe that you
could cut through the intermediate tree structure as follows. Is there
any downside?

type 'a delayed_tree = 'a cascade -> 'a cascade

let delayed_tree_to_cascade k = k nil
let delayed_tree_to_iterator (dt : 'a delayed_tree) : 'a iterator =
  cascade_to_iterator (delayed_tree_to_cascade dt)

type 'a delay = 'a

class ['self] delayed_tree_monoid = object (_ : 'self)
  method zero =
    fun k -> k

  method plus s1 s2 =
    fun k -> s1 (s2 k)

  method visit_delay
    : 'env 'a .
      ('env -> 'a -> 'b delayed_tree) ->
      'env -> 'a delay -> 'b delayed_tree
    = fun visit_ env x k ->
        (fun () -> visit_ env x k ())
end

let yield _env x = fun k () -> Cons (x, k)

On Thu, Mar 9, 2017 at 1:33 PM, François Pottier
<francois.pottier@inria.fr> wrote:
>
> Dear KC,
>
> On 09/03/2017 12:53, KC Sivaramakrishnan wrote:
>>
>> Thanks for the wonderful library and the excellent documentation. I have
>> a feature request. Could you provide a python-style generator for
>> traversing the data structure on demand? For a binary tree:
>>
>>      type 'a t = Leaf | Node of 'a t * 'a * 'a t
>>
>> I envision a `mk_gen` function:
>>
>>      val mk_gen : 'a t -> (unit -> 'a option)
>>      (** [mk_gen t] returns a generator function [f], which when invoked
>>          performs 1-step of the traversal and returns [Some v], where [v]
>>          is the node value. [f] returns [None] when the traversal is done.
>> *)
>
>
> Thanks for this excellent question, which I had not thought about.
>
> A quick answer might be that, if you are using OCaml + effect handlers,
> it should be fairly easy for you to perform control inversion and turn
> a producer-controlled traversal (as performed by an [iter] visitor) into
> a consumer-controlled traversal.
>
> That said, I was able to come up with a solution in pure OCaml. It is
> somewhat
> unexpected and (I think) quite nice, so I am posting it (with comments) on
> the
> list (see attached file). If there is demand, most of this code could be
> made
> part of the VisitorsRuntime library.
>
> Best regards,
>
>
> --
> François Pottier
> francois.pottier@inria.fr
> http://gallium.inria.fr/~fpottier/
>
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