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{-# 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
|
