From fd88f102169a276f6379fbbc1a2baa68aa3b2621 Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Sat, 31 May 2014 12:36:15 +0200
Subject: [PATCH] safe version of fold_right

---
 core/CCList.ml  | 20 ++++++++++++++++++++
 core/CCList.mli |  3 +++
 2 files changed, 23 insertions(+)

diff --git a/core/CCList.ml b/core/CCList.ml
index a60428db..45a31ccc 100644
--- a/core/CCList.ml
+++ b/core/CCList.ml
@@ -61,6 +61,26 @@ let append l1 l2 =
 
 let (@) = append
 
+let fold_right f l acc =
+  let rec direct i f l acc = match l with
+    | [] -> acc
+    | _ when i=0 -> safe f (List.rev l) acc
+    | x::l' ->
+        let acc = direct (i-1) f l' acc in
+        f x acc
+  and safe f l acc = match l with
+    | [] -> acc
+    | x::l' ->
+        let acc = f x acc in
+        safe f l' acc
+  in
+  direct _direct_depth f l acc
+
+(*$T
+  fold_right (+) (1 -- 1_000_000) 0 = \
+    List.fold_left (+) 0 (1 -- 1_000_000)
+*)
+
 let rec compare f l1 l2 = match l1, l2 with
   | [], [] -> 0
   | _, [] -> 1
diff --git a/core/CCList.mli b/core/CCList.mli
index 6f9adf77..f06284f1 100644
--- a/core/CCList.mli
+++ b/core/CCList.mli
@@ -36,6 +36,9 @@ val append : 'a t -> 'a t -> 'a t
 
 val (@) : 'a t -> 'a t -> 'a t
 
+val fold_right : ('a -> 'b -> 'b) -> 'a t -> 'b -> 'b
+(** Safe version of [fold_right] *)
+
 val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
 
 val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool