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{-# LANGUAGE RecordWildCards #-}
module Xmobar.Plugins.QueueReader
(QueueReader (..)
) where
import Xmobar.Run.Exec (Exec (..))
import Control.Monad (forever)
import qualified Control.Concurrent.STM as STM
-- | A 'QueueReader' displays data from an 'TQueue a' where
-- the data items 'a' are rendered by a user supplied function.
--
-- Like the 'HandleReader' plugin this is only useful if you are
-- running @xmobar@ from other Haskell code. You should create a
-- new @TQueue a@ and pass it to this plugin.
--
-- @
-- main :: IO
-- main = do
-- q <- STM.newQueueIO @String
-- bar <- forkIO $ xmobar conf
-- { commands = Run (QueueReader q id "Queue") : commands conf }
-- STM.atomically $ STM.writeTQueue q "Some Message"
-- @
data QueueReader a
= QueueReader
{ qQueue :: STM.TQueue a
, qShowItem :: a -> String
, qName :: String
}
-- | This cannot be read back.
instance Show (QueueReader a) where
-- | Only show the name/alias for the queue reader.
show q = "QueueReader " <> qName q
-- | WARNING: This read instance will throw an exception if used! It is
-- only implemented, because it is required by 'Xmobar.Run` in 'Xmobar.commands'.
instance Read (QueueReader a) where
-- | Throws an 'error'!
readsPrec = error "QueueReader: instance is a stub"
-- | Async queue/channel reading.
instance Exec (QueueReader a) where
-- | Read from queue as data arrives.
start QueueReader{..} cb =
forever (STM.atomically (qShowItem <$> STM.readTQueue qQueue) >>= cb)
alias = qName
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