add CCIO.File.walk_iter

src/core/CCIO.ml

@@ -3,6 +3,7 @@
 
 (** {1 IO Utils} *)
 
+type 'a iter = ('a -> unit) -> unit
 type 'a or_error = ('a, string) result
 type 'a gen = unit -> 'a option
 
@@ -33,6 +34,10 @@ let gen_of_array arr =
       Some x
     )
 
+let rec gen_iter f g = match g() with
+  | None -> ()
+  | Some x -> f x; gen_iter f g
+
 let gen_flat_map f next_elem =
   let state = ref `Init in
   let rec next() =
@@ -386,6 +391,7 @@ module File = struct
   *)
 
   let walk_seq d = seq_of_gen_ (walk d)
+  let walk_iter d = fun yield -> gen_iter yield (walk d)
 
   let walk_l d =
     let l = ref [] in

src/core/CCIO.mli

@@ -53,6 +53,7 @@
 *)
 
 type 'a or_error = ('a, string) result
+type 'a iter = ('a -> unit) -> unit
 type 'a gen = unit -> 'a option
 (** See [Gen] in the {{: https://github.com/c-cube/gen} gen library}. *)
 
@@ -250,6 +251,10 @@ module File : sig
       symlinks, etc.)
       @raise Sys_error in case of error (e.g. permission denied) during iteration. *)
 
+  val walk_iter : t -> walk_item iter
+  (** Like {!walk} but with an imperative iterator.
+      @since NEXT_RELEASE *)
+
   val walk_l : t -> walk_item list
   (** Like {!walk} but returns a list (therefore it's eager and might
       take some time on large directories).