never executed always true always false

    1 module UnliftIO.MessageBox.Util.CallId
    2   ( CallId (MkCallId),
    3     HasCallIdCounter (..),
    4     takeNext,
    5     newCallIdCounter,
    6   )
    7 where
    8 
    9 import Control.Monad.Reader (MonadReader, asks)
   10 import UnliftIO.MessageBox.Util.Fresh
   11   ( CounterVar,
   12     incrementAndGet,
   13     newCounterVar,
   14   )
   15 import UnliftIO (MonadIO, MonadUnliftIO)
   16 
   17 -- | An identifier value every command send by 'call's.
   18 newtype CallId = MkCallId Int
   19   deriving newtype (Eq, Ord)
   20 
   21 instance Show CallId where
   22   showsPrec _ (MkCallId !i) =
   23     showChar '<' . shows i . showChar '>'
   24 
   25 -- | Class of environment records containing a 'CounterVar' for 'CallId's.
   26 class HasCallIdCounter env where
   27   getCallIdCounter :: env -> CounterVar CallId
   28 
   29 instance HasCallIdCounter (CounterVar CallId) where
   30   {-# INLINE getCallIdCounter #-}
   31   getCallIdCounter = id
   32 
   33 -- | Create a new 'CallId' 'CounterVar'.
   34 {-# INLINE newCallIdCounter #-}
   35 newCallIdCounter :: MonadIO m => m (CounterVar CallId)
   36 newCallIdCounter = newCounterVar
   37 
   38 -- | Increment and get a new 'CallId'.
   39 {-# INLINE takeNext #-}
   40 takeNext :: (MonadReader env m, HasCallIdCounter env, MonadUnliftIO m) => m CallId
   41 takeNext = asks getCallIdCounter >>= incrementAndGet