add range (like python) and id helper functions

lib/utils.ml

@@ -25,3 +25,11 @@ let uncurry3 f (x, y, z) = f x y z
 let swap x y = y x
 
 let pair_of_list l = (List.hd l, List.tl l |> List.hd)
+
+let range x =
+    let rec aux n res =
+        if n = 0 then res
+        else aux (n - 1) (n :: res) in
+    aux x []
+
+let id x = x