add List.iter_up_to

lib/server/import.ml

@@ -30,6 +30,14 @@ module List = struct
     [@@tail_mod_cons]
     in
     iter xs
+
+  let iter_up_to f xs ~limit =
+    let rec iter n = function
+      | x :: xs when n > 0 ->
+        f x; iter (n - 1) xs
+      | _ -> ()
+    in
+    iter limit xs
 end
 
 include (val Logging.logs "Irc")

lib/server/test_list.ml

@@ -12,6 +12,7 @@ let%expect_test _ =
     iter "[" "[]" xs
   in
 
+  let print_int_sp x = print_int x; print_string " " in
   let print_ints_nl xs = print_list print_int xs; print_newline () in
 
   print_ints_nl
@@ -23,3 +24,8 @@ let%expect_test _ =
        [1;2;3;1;2]);
   [%expect {| [1;2;3;4;5;6;7;8;9;1;2;3;4;5;6] |}];
 
+  List.iter_up_to ~limit:5
+    print_int_sp
+    [1;2;3;4;5;6;7;8;9];
+  print_newline ();
+  [%expect {| 1 2 3 4 5 |}];