fold_while impl for CCList and CCArray

src/core/CCArray.ml

@@ -53,6 +53,11 @@ module type S = sig
   val foldi : ('b -> int -> 'a -> 'b) -> 'b -> 'a t -> 'b
   (** fold left on array, with index *)
 
+  val fold_while : ('a -> 'b -> 'a * [`Stop | `Continue]) -> 'a -> 'b t -> 'a
+  (** fold left on array until a stop condition via [('a, `Stop)] is
+      indicated by the accumulator
+      @since NEXT_RELEASE *)
+
   val iter : ('a -> unit) -> 'a t -> unit
 
   val iteri : (int -> 'a -> unit) -> 'a t -> unit
@@ -276,6 +281,20 @@ let fold = Array.fold_left
 
 let foldi f acc a = _foldi f acc a 0 (Array.length a)
 
+let fold_while f acc a =
+  let rec fold_while_i f acc i =
+    if i < Array.length a then
+      let acc, cont = f acc a.(i) in
+      match cont with
+      | `Stop -> acc
+      | `Continue -> fold_while_i f acc (i+1)
+    else acc
+  in fold_while_i f acc 0
+
+(*$T
+  fold_while (fun acc b -> if b then acc+1, `Continue else acc, `Stop) 0 (Array.of_list [true;true;false;true]) = 2
+*)
+
 let iter = Array.iter
 
 let iteri = Array.iteri
@@ -480,6 +499,16 @@ module Sub = struct
 
   let foldi f acc a = _foldi f acc a.arr a.i a.j
 
+  let fold_while f acc a =
+    let rec fold_while_i f acc i =
+      if i < Array.length a.arr && i < a.j then
+        let acc, cont = f acc a.arr.(i) in
+        match cont with
+        | `Stop -> acc
+        | `Continue -> fold_while_i f acc (i+1)
+      else acc
+    in fold_while_i f acc a.i
+
   let get a i =
     let j = a.i + i in
     if i<0 || j>=a.j then invalid_arg "Array.Sub.get";

src/core/CCArray.mli

@@ -50,10 +50,15 @@ module type S = sig
 
   val length : _ t -> int
 
-  val fold : ('b -> 'a -> 'b) -> 'b -> 'a t -> 'b
+  val fold : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'a
 
-  val foldi : ('b -> int -> 'a -> 'b) -> 'b -> 'a t -> 'b
-  (** fold left on array, with index *)
+  val foldi : ('a -> int -> 'b -> 'a) -> 'a -> 'b t -> 'a
+  (** Fold left on array, with index *)
+
+  val fold_while : ('a -> 'b -> 'a * [`Stop | `Continue]) -> 'a -> 'b t -> 'a
+  (** Fold left on array until a stop condition via [('a, `Stop)] is
+      indicated by the accumulator
+      @since NEXT_RELEASE *)
 
   val iter : ('a -> unit) -> 'a t -> unit
 

src/core/CCList.ml

@@ -116,6 +116,17 @@ let fold_right f l acc =
     l = fold_right (fun x y->x::y) l [])
 *)
 
+let rec fold_while f acc = function
+  | [] -> acc
+  | e::l -> let acc, cont = f acc e in
+    match cont with
+    | `Stop -> acc
+    | `Continue -> fold_while f acc l
+
+(*$T
+  fold_while (fun acc b -> if b then acc+1, `Continue else acc, `Stop) 0 [true;true;false;true] = 2
+*)
+
 let init len f =
   let rec init_rec acc i f =
     if i=0 then f i :: acc

src/core/CCList.mli

@@ -48,6 +48,11 @@ val filter : ('a -> bool) -> 'a t -> 'a t
 val fold_right : ('a -> 'b -> 'b) -> 'a t -> 'b -> 'b
 (** Safe version of [fold_right] *)
 
+val fold_while : ('a -> 'b -> 'a * [`Stop | `Continue]) -> 'a -> 'b t -> 'a
+(** Fold until a stop condition via [('a, `Stop)] is
+    indicated by the accumulator
+    @since NEXT_RELEASE *)
+
 val init : int -> (int -> 'a) -> 'a t
 (** Same as [Array.init]
     @since 0.6 *)