merge from master

sequence.ml

@@ -336,9 +336,9 @@ let take n seq k =
   let count = ref 0 in
   try
     seq (fun x ->
+      if !count = n then raise ExitSequence;
       incr count;
       k x;
-      if !count = n then raise ExitSequence
     )
   with ExitSequence -> ()
 
@@ -436,14 +436,17 @@ let to_list seq = List.rev (fold (fun y x -> x::y) [] seq)
 
 let to_rev_list seq = fold (fun y x -> x :: y) [] seq
 
+let of_list l k = List.iter k l
+
+let on_list f l =
+  to_list (f (of_list l))
+
 let to_opt = head
 
 let of_opt o k = match o with
   | None -> ()
   | Some x -> k x
 
-let of_list l k = List.iter k l
-
 let to_array seq =
   let l = MList.of_seq seq in
   let n = MList.length l in
@@ -767,5 +770,3 @@ module IO = struct
   let write_lines ?mode ?flags filename seq =
     write_to ?mode ?flags filename (snoc (intersperse "\n" seq) "\n")
 end
-
-

sequence.mli

@@ -319,6 +319,11 @@ val to_rev_list : 'a t -> 'a list
 
 val of_list : 'a list -> 'a t
 
+val on_list : ('a t -> 'b t) -> 'a list -> 'b list
+(** [on_list f l] is equivalent to [to_list @@ f @@ of_list l].
+    @since NEXT_RELEASE
+*)
+
 val to_opt : 'a t -> 'a option
   (** Alias to {!head}
       @since 0.5.1 *)

tests/test_sequence.ml

@@ -190,6 +190,13 @@ let test_int_range () =
   OUnit.assert_equal ~printer:pp_ilist [] S.(to_list (10 --^ 60));
   ()
 
+let test_take () =
+  let l = S.(to_list (take 0 (of_list [1]))) in
+  OUnit.assert_equal ~printer:pp_ilist [] l;
+  let l = S.(to_list (take 5 (of_list [1;2;3;4;5;6;7;8;9;10]))) in
+  OUnit.assert_equal ~printer:pp_ilist [1;2;3;4;5] l;
+  ()
+
 let suite =
   "test_sequence" >:::
     [ "test_empty" >:: test_empty;
@@ -217,4 +224,5 @@ let suite =
       "test_unfoldr" >:: test_unfoldr;
       "test_hashtbl" >:: test_hashtbl;
       "test_int_range" >:: test_int_range;
+      "test_take" >:: test_take;
     ]