From ea2a725e9d5d758495b556631c3280de9d97fa0a Mon Sep 17 00:00:00 2001
From: Alexander Foremny <aforemny@posteo.de>
Date: Wed, 10 Apr 2024 14:05:08 +0200
Subject: init

---
 app/Util.hs | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)
 create mode 100644 app/Util.hs

(limited to 'app/Util.hs')

diff --git a/app/Util.hs b/app/Util.hs
new file mode 100644
index 0000000..308ef88
--- /dev/null
+++ b/app/Util.hs
@@ -0,0 +1,18 @@
+{-# LANGUAGE BlockArguments #-}
+
+module Util
+  ( stmChanges,
+  )
+where
+
+import UnliftIO.STM
+
+stmChanges :: (Eq a) => STM a -> IO (STM a)
+stmChanges mkX = do
+  x'T <- newTVarIO Nothing
+  pure do
+    x' <- readTVar x'T
+    x <- mkX
+    checkSTM (Just x /= x')
+    writeTVar x'T (Just x)
+    pure x
-- 
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