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/