From 54a131a2629d14ca6a0bb51d8e3b1ed4bb573bfe Mon Sep 17 00:00:00 2001
From: Gabriel Scherer <gabriel.scherer@gmail.com>
Date: Sun, 16 Jun 2013 16:19:30 +0000
Subject: [PATCH] PR#4079: Queue.copy is now tail-recursive (patch from
 "Cristophe" on the bugtracker)

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13784 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
---
 Changes         |  1 +
 stdlib/queue.ml | 13 +++++++------
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/Changes b/Changes
index 932a3263b..5b8c32cea 100644
--- a/Changes
+++ b/Changes
@@ -56,6 +56,7 @@ Runtime system:
 Bug fixes:
 - PR#3679: Warning display problems
 - PR#3963: Graphics.wait_next_event in Win32 hangs if window closed
+- PR#4079: Queue.copy is now tail-recursive
 - PR#4762: ?? is not used at all, but registered as a lexer token
 - PR#4887: input_char after close_in crashes ocaml (msvc runtime)
 - PR#4994: ocaml-mode doesn't work with xemacs21
diff --git a/stdlib/queue.ml b/stdlib/queue.ml
index 6d82d2593..fb920d8c9 100644
--- a/stdlib/queue.ml
+++ b/stdlib/queue.ml
@@ -107,14 +107,15 @@ let copy q =
       next = tail'
     } in
 
-    let rec copy cell =
-      if cell == tail then tail'
-      else {
+    let rec copy prev cell =
+      if cell != tail
+      then let res = {
         content = cell.content;
-        next = copy cell.next
-      } in
+        next = tail'
+      } in prev.next <- res;
+      copy res cell.next in
 
-    tail'.next <- copy tail.next;
+    copy tail' tail.next;
     {
       length = q.length;
       tail = tail'