Implement range_iter function

lib/toolbox/utils.ml

@@ -14,6 +14,15 @@ let tree_from_file ?(alpha = 1.) fn =
         length, condition
       )
 
+let range_iter a b ~f =
+  let rec loop i=
+    if i < b then (
+      f i ; 
+      loop (i + 1)
+    )
+  in 
+  loop a
+
 let int_fold a b ~init ~f =
   let rec loop acc i =
     if i >= b then acc else loop (f acc i) (i + 1)