{-# LANGUAGE UndecidableInstances #-}
-- | The 'LogWriter' type encapsulates an effectful function to write 'LogMessage's.
--
-- Used in conjunction with the 'HandleLogWriter' class, it
-- can be used to write messages from within an effectful
-- computation.
module Control.Eff.Log.Writer
(
-- * 'LogWriter' Definition
LogWriter(..)
-- * LogWriter Reader Effect
, LogWriterReader
, localLogWriterReader
, askLogWriter
, runLogWriterReader
-- * LogWriter Handler Class
, HandleLogWriter(..)
, noOpLogWriter
, PureLogWriter(..)
-- ** Writer Combinator
-- *** Pure Writer Combinator
, filteringLogWriter
, mappingLogWriter
-- *** Impure Writer Combinator
, mappingLogWriterM
)
where
import Control.Eff
import Control.Eff.Extend
import Control.Eff.Log.Message
import Data.Default
import Data.Function ( fix )
import Data.Functor.Identity ( Identity )
import Control.DeepSeq ( force )
import Control.Monad ( (>=>)
, when
)
import Control.Monad.Base ( MonadBase() )
import qualified Control.Monad.Catch as Catch
import Control.Monad.Trans.Control ( MonadBaseControl
( restoreM
, liftBaseWith
, StM
)
)
import Data.Kind
import Control.Lens
-- | A function that takes a log message and returns an effect that
-- /logs/ the message.
newtype LogWriter writerM = MkLogWriter
{ runLogWriter :: LogMessage -> writerM ()
}
instance Applicative w => Default (LogWriter w) where
def = MkLogWriter (const (pure ()))
-- | Provide the 'LogWriter'
--
-- Exposed for custom extensions, if in doubt use 'withLogging'.
runLogWriterReader :: LogWriter h -> Eff (LogWriterReader h ': e) a -> Eff e a
runLogWriterReader e m = fix (handle_relay (\x _ -> return x)) m e
-- | Get the current 'LogWriter'.
askLogWriter
:: SetMember LogWriterReader (LogWriterReader h) e => Eff e (LogWriter h)
askLogWriter = send AskLogWriter
-- | Modify the current 'LogWriter'.
localLogWriterReader
:: forall h e a
. SetMember LogWriterReader (LogWriterReader h) e
=> (LogWriter h -> LogWriter h)
-> Eff e a
-> Eff e a
localLogWriterReader f m =
f
<$> askLogWriter
>>= fix (respond_relay @(LogWriterReader h) (\x _ -> return x)) m
-- | A Reader specialized for 'LogWriter's
--
-- The existing @Reader@ couldn't be used together with 'SetMember', so this
-- lazy reader was written, specialized to reading 'LogWriter'.
data LogWriterReader h v where
AskLogWriter ::LogWriterReader h (LogWriter h)
instance Handle (LogWriterReader h) e a (LogWriter h -> k) where
handle k q AskLogWriter lw = k (q ^$ lw) lw
instance forall h m r. (MonadBase m m, LiftedBase m r)
=> MonadBaseControl m (Eff (LogWriterReader h ': r)) where
type StM (Eff (LogWriterReader h ': r)) a = StM (Eff r) a
liftBaseWith f = do
lf <- askLogWriter
raise (liftBaseWith (\runInBase -> f (runInBase . runLogWriterReader lf)))
restoreM = raise . restoreM
instance (LiftedBase m e, Catch.MonadThrow (Eff e))
=> Catch.MonadThrow (Eff (LogWriterReader h ': e)) where
throwM exception = raise (Catch.throwM exception)
instance (Applicative m, LiftedBase m e, Catch.MonadCatch (Eff e))
=> Catch.MonadCatch (Eff (LogWriterReader h ': e)) where
catch effect handler = do
lf <- askLogWriter
let lower = runLogWriterReader lf
nestedEffects = lower effect
nestedHandler exception = lower (handler exception)
raise (Catch.catch nestedEffects nestedHandler)
instance (Applicative m, LiftedBase m e, Catch.MonadMask (Eff e))
=> Catch.MonadMask (Eff (LogWriterReader h ': e)) where
mask maskedEffect = do
lf <- askLogWriter
let lower :: Eff (LogWriterReader h ': e) a -> Eff e a
lower = runLogWriterReader lf
raise
(Catch.mask
(\nestedUnmask -> lower (maskedEffect (raise . nestedUnmask . lower)))
)
uninterruptibleMask maskedEffect = do
lf <- askLogWriter
let lower :: Eff (LogWriterReader h ': e) a -> Eff e a
lower = runLogWriterReader lf
raise
(Catch.uninterruptibleMask
(\nestedUnmask -> lower (maskedEffect (raise . nestedUnmask . lower)))
)
generalBracket acquire release useIt = do
lf <- askLogWriter
let lower :: Eff (LogWriterReader h ': e) a -> Eff e a
lower = runLogWriterReader lf
raise
(Catch.generalBracket (lower acquire)
(((.) . (.)) lower release)
(lower . useIt)
)
-- * 'LogWriter' Zoo
-- | The instances of this class are the monads that define (side-) effect(s) of writting logs.
class HandleLogWriter (writerEff :: Type -> Type) where
-- | A list of effects that are required for writing the log messages.
-- For example 'Lift IO' or '[]' for pure log writers.
type LogWriterEffects writerEff :: [Type -> Type]
-- | Run the side effect of a 'LogWriter' in a compatible 'Eff'.
handleLogWriterEffect :: (LogWriterEffects writerEff <:: e) => writerEff () -> Eff e ()
-- | Write a message using the 'LogWriter' found in the environment.
--
-- The semantics of this function are a combination of 'runLogWriter' and 'handleLogWriterEffect',
-- with the 'LogWriter' read from a 'LogWriterReader'.
liftWriteLogMessage :: ( SetMember LogWriterReader (LogWriterReader writerEff) e
, LogWriterEffects writerEff <:: e)
=> LogMessage
-> Eff e ()
liftWriteLogMessage m = do
w <- askLogWriter
handleLogWriterEffect (runLogWriter w m)
instance HandleLogWriter IO where
type LogWriterEffects IO = '[Lift IO]
handleLogWriterEffect = send . Lift
-- ** Pure Log Writers
-- | A phantom type for the 'HandleLogWriter' class for /pure/ 'LogWriter's
newtype PureLogWriter a = MkPureLogWriter { runPureLogWriter :: Identity a }
deriving (Applicative, Functor, Monad)
-- | A 'LogWriter' monad for 'Debug.Trace' based pure logging.
instance HandleLogWriter PureLogWriter where
type LogWriterEffects PureLogWriter = '[]
handleLogWriterEffect lw = return (force (runIdentity (force (runPureLogWriter lw))))
-- | This 'LogWriter' will discard all messages.
--
-- NOTE: This is just an alias for 'def'
noOpLogWriter :: Applicative m => LogWriter m
noOpLogWriter = def
-- | A 'LogWriter' that applies a predicate to the 'LogMessage' and delegates to
-- to the given writer of the predicate is satisfied.
filteringLogWriter :: Monad e => LogPredicate -> LogWriter e -> LogWriter e
filteringLogWriter p lw =
MkLogWriter (\msg -> when (p msg) (runLogWriter lw msg))
-- | A 'LogWriter' that applies a function to the 'LogMessage' and delegates the result to
-- to the given writer.
mappingLogWriter :: (LogMessage -> LogMessage) -> LogWriter e -> LogWriter e
mappingLogWriter f lw = MkLogWriter (runLogWriter lw . f)
-- | Like 'mappingLogWriter' allow the function that changes the 'LogMessage' to have effects.
mappingLogWriterM
:: Monad e => (LogMessage -> e LogMessage) -> LogWriter e -> LogWriter e
mappingLogWriterM f lw = MkLogWriter (f >=> runLogWriter lw)