From 4aed639cc79bb1332ce800c8f7d8cda3ee792917 Mon Sep 17 00:00:00 2001
From: Hongchang Wu <wuhc85@gmail.com>
Date: Sat, 8 Jan 2022 21:23:11 -0500
Subject: [PATCH] Add CCSeq.zip_with

---
 src/core/CCSeq.ml  | 12 ++++++++++++
 src/core/CCSeq.mli |  6 ++++++
 2 files changed, 18 insertions(+)

diff --git a/src/core/CCSeq.ml b/src/core/CCSeq.ml
index 55a32593..c1e5b435 100644
--- a/src/core/CCSeq.ml
+++ b/src/core/CCSeq.ml
@@ -341,6 +341,18 @@ let rec zip a b () = match a(), b() with
   | _, Nil -> Nil
   | Cons (x, a'), Cons (y, b') -> Cons ((x,y), zip a' b')
 
+let rec zip_with f a b () = match a(), b() with
+  | Nil, _
+  | _, Nil -> Nil
+  | Cons (x, a'), Cons (y, b') -> Cons (f x y, zip_with f a' b')
+
+(*$Q
+  Q.(pair (list int) (list int)) (fun (l1, l2) -> \
+    let l1 = of_list l1 in \
+    let l2 = of_list l2 in \
+    zip l1 l2 |> to_list = (zip_with (fun x y -> (x, y)) l1 l2 |> to_list))
+*)
+
 let unzip l =
   let rec first l () = match l() with
     | Nil -> Nil
diff --git a/src/core/CCSeq.mli b/src/core/CCSeq.mli
index 1719ba92..bb7ddf82 100644
--- a/src/core/CCSeq.mli
+++ b/src/core/CCSeq.mli
@@ -178,6 +178,12 @@ val zip : 'a t -> 'b t -> ('a * 'b) t
 (** Combine elements pairwise. Stop as soon as one of the lists stops.
     @since 0.13 *)
 
+val zip_with : ('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t
+(** Generalization of {!zip}. Combine elements with the function given as the first
+    argument. Stop as soon as one of the lists stops.
+
+    @since NEXT_RELEASE *)
+
 val unzip : ('a * 'b) t -> 'a t * 'b t
 (** Split each tuple in the list.
     @since 0.13 *)