add CCList.{take,drop}_while; improve map performance

src/core/CCList.ml

@@ -40,12 +40,16 @@ let direct_depth_default_ = 1000
 let map f l =
   let rec direct f i l = match l with
     | [] -> []
-    | _ when i=0 -> safe f l
-    | x::l' ->
-        let y = f x in
-        y :: direct f (i-1) l'
-  and safe f l =
-    List.rev (List.rev_map f l)
+    | [x] -> [f x]
+    | [x1;x2] -> let y1 = f x1 in [y1; f x2]
+    | [x1;x2;x3] -> let y1 = f x1 in let y2 = f x2 in [y1; y2; f x3]
+    | _ when i=0 -> List.rev (List.rev_map f l)
+    | x1::x2::x3::x4::l' ->
+        let y1 = f x1 in
+        let y2 = f x2 in
+        let y3 = f x3 in
+        let y4 = f x4 in
+        y1 :: y2 :: y3 :: y4 :: direct f (i-1) l'
   in
   direct f direct_depth_default_ l
 
@@ -395,6 +399,13 @@ let take n l =
   take 300_000 (1 -- 400_000) = 1 -- 300_000
 *)
 
+(*$Q
+  (Q.pair (Q.list Q.small_int) Q.int) (fun (l,i) -> \
+    let i = abs i in \
+    let l1 = take i l in \
+    List.length l1 <= i && ((List.length l1 = i) = (List.length l >= i)))
+*)
+
 let rec drop n l = match l with
   | [] -> []
   | _ when n=0 -> l
@@ -411,6 +422,41 @@ let split = take_drop
     l1 @ l2 = l )
 *)
 
+let take_while p l =
+  let rec direct i p l = match l with
+    | [] -> []
+    | _ when i=0 -> safe p [] l
+    | x :: l' ->
+        if p x then x :: direct (i-1) p l' else []
+  and safe p acc l = match l with
+    | [] -> List.rev acc
+    | x :: l' ->
+        if p x then safe p (x::acc) l' else List.rev acc
+  in
+  direct direct_depth_default_ p l
+
+(*$T
+  take_while (fun x->x<10) (1 -- 20) = (1--9)
+  take_while (fun x->x <> 0) [0;1;2;3] = []
+  take_while (fun _ -> true) [] = []
+  take_while (fun _ -> true) (1--10) = (1--10)
+*)
+
+(*$Q
+  Q.(pair (fun1 small_int bool) (list small_int)) (fun (f,l) -> \
+    let l1 = take_while f l in \
+    List.for_all f l1)
+*)
+
+let rec drop_while p l = match l with
+  | [] -> []
+  | x :: l' -> if p x then drop_while p l' else l
+
+(*$Q
+  Q.(pair (fun1 small_int bool) (list small_int)) (fun (f,l) -> \
+    take_while f l @ drop_while f l = l)
+*)
+
 let last n l =
   let len = List.length l in
   if len < n then l else drop (len-n) l

src/core/CCList.mli

@@ -118,6 +118,12 @@ val take_drop : int -> 'a t -> 'a t * 'a t
 (** [take_drop n l] returns [l1, l2] such that [l1 @ l2 = l] and
     [length l1 = min (length l) n] *)
 
+val take_while : ('a -> bool) -> 'a t -> 'a t
+(** @since NEXT_RELEASE *)
+
+val drop_while : ('a -> bool) -> 'a t -> 'a t
+(** @since NEXT_RELEASE *)
+
 val split : int -> 'a t -> 'a t * 'a t
 (** synonym to {!take_drop}
     @deprecated since NEXT_RELEASE: conflict with the {!List.split} standard function *)