From 2083590773f11508c92359b0ad43ad0383a69a6d Mon Sep 17 00:00:00 2001
From: carm <carmelo.piccione@gmail.com>
Date: Sat, 3 Jan 2015 13:13:54 -0500
Subject: [PATCH 1/2] fold_while impl for sequences

---
 sequence.ml            | 15 +++++++++++++++
 sequence.mli           |  7 ++++++-
 tests/test_sequence.ml |  6 ++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/sequence.ml b/sequence.ml
index 6c6bd3b..2fefe5f 100644
--- a/sequence.ml
+++ b/sequence.ml
@@ -347,6 +347,21 @@ let take_while p seq k =
     seq (fun x -> if p x then k x else raise ExitTakeWhile)
   with ExitTakeWhile -> ()
 
+exception ExitFoldWhile
+
+let fold_while f s seq =
+  let state = ref s in
+  let consume x =
+      let acc, cont = f (!state) x in
+      state := acc;
+      match cont with
+      | `Stop -> raise ExitFoldWhile
+      | `Continue -> ()
+  in
+  try
+    seq consume; !state
+  with ExitFoldWhile -> !state
+
 let drop n seq k =
   let count = ref 0 in
   seq (fun x -> if !count >= n then k x else incr count)
diff --git a/sequence.mli b/sequence.mli
index 677f79c..ce6c318 100644
--- a/sequence.mli
+++ b/sequence.mli
@@ -119,7 +119,7 @@ val iter : ('a -> unit) -> 'a t -> unit
 val iteri : (int -> 'a -> unit) -> 'a t -> unit
   (** Iterate on elements and their index in the sequence *)
 
-val fold : ('b -> 'a -> 'b) -> 'b -> 'a t -> 'b
+val fold : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'a
   (** Fold over elements of the sequence, consuming it *)
 
 val foldi : ('b -> int -> 'a -> 'b) -> 'b -> 'a t -> 'b
@@ -272,6 +272,11 @@ val take_while : ('a -> bool) -> 'a t -> 'a t
       Will work on an infinite sequence [s] if the predicate is false for at
       least one element of [s]. *)
 
+val fold_while : ('a -> 'b -> 'a * [`Stop | `Continue]) -> 'a -> 'b t -> 'a
+  (** Folds over elements of the sequence, stopping early if the accumulator
+      returns [('a, `Stop)]
+      @since NEXT_RELEASE *)
+
 val drop : int -> 'a t -> 'a t
   (** Drop the [n] first elements of the sequence. Lazy. *)
 
diff --git a/tests/test_sequence.ml b/tests/test_sequence.ml
index 30f0f1c..8fd1b17 100644
--- a/tests/test_sequence.ml
+++ b/tests/test_sequence.ml
@@ -42,6 +42,12 @@ let test_foldi () =
   OUnit.assert_equal [1, "world"; 0, "hello"] l;
   ()
 
+let test_fold_while () =
+  let n = S.of_list [true;true;false;true]
+    |> S.fold_while (fun acc b -> if b then acc+1, `Continue else acc, `Stop) 0 in
+  OUnit.assert_equal 2 n;
+  ()
+
 let test_exists () =
   S.(1 -- 100)
     |> S.exists (fun x -> x = 59)

From beb50229ad96d9e98c53fa2fdc60c51482e6d77f Mon Sep 17 00:00:00 2001
From: carm <carmelo.piccione@gmail.com>
Date: Sat, 3 Jan 2015 13:16:56 -0500
Subject: [PATCH 2/2] fix foldi to have 'a param first

---
 sequence.mli | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sequence.mli b/sequence.mli
index ce6c318..7957890 100644
--- a/sequence.mli
+++ b/sequence.mli
@@ -122,7 +122,7 @@ val iteri : (int -> 'a -> unit) -> 'a t -> unit
 val fold : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'a
   (** Fold over elements of the sequence, consuming it *)
 
-val foldi : ('b -> int -> 'a -> 'b) -> 'b -> 'a t -> 'b
+val foldi : ('a -> int -> 'b -> 'a) -> 'a -> 'b t -> 'a
   (** Fold over elements of the sequence and their index, consuming it *)
 
 val map : ('a -> 'b) -> 'a t -> 'b t