1 files changed, 18 insertions, 0 deletions
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