From bb4cfebd31ad44bd0a31e0959e145fced3078760 Mon Sep 17 00:00:00 2001
From: Joe Crayne <joe@jerkface.net>
Date: Thu, 30 May 2019 01:52:32 -0400
Subject: Fix updateBack ring-buffer bug.

---
 RingBuffer.hs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/RingBuffer.hs b/RingBuffer.hs
index b2779d7..64b0624 100644
--- a/RingBuffer.hs
+++ b/RingBuffer.hs
@@ -66,5 +66,7 @@ pushBack r upd = do
 
 updateBack :: RingBuffer u -> u -> IO ()
 updateBack r upd = do
-    back <- readIORef $ rBack r
-    updateBuffer (rBuffer r) back upd
+    size <- readIORef $ rSize r
+    when (size > 0) $ do
+        back <- readIORef $ rBack r
+        updateBuffer (rBuffer r) (mod (back + ringCapacity r - 1) (ringCapacity r)) upd
-- 
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