Control.Monad.Logger

This module provides the facilities needed for a decoupled logging system.

The MonadLogger class is implemented by monads that give access to a logging facility. If you're defining a custom monad, then you may define an instance of MonadLogger that routes the log messages to the appropriate place (e.g., that's what yesod-core's GHandler does). Otherwise, you may use the LoggingT monad included in this module (see runStderrLoggingT). To simply discard log message, use NoLoggingT.

As a user of the logging facility, we provide you some convenient Template Haskell splices that use the MonadLogger class. They will record their source file and position, which is very helpful when debugging. See logDebug for more information.

MonadLogger

class Monad m => MonadLogger m where

A Monad which has the ability to log messages in some manner.

Minimal complete definition

Nothing

Methods

monadLoggerLog :: ToLogStr msg => Loc -> LogSource -> LogLevel -> msg -> m ()

Instances

MonadLogger m => MonadLogger (MaybeT m)

MonadLogger m => MonadLogger (ListT m)

MonadLogger m => MonadLogger (ResourceT m)

MonadLogger m => MonadLogger (IdentityT m)

MonadIO m => MonadLogger (LoggingT m)

Monad m => MonadLogger (NoLoggingT m)

(MonadLogger m, Monoid w) => MonadLogger (WriterT w m)

(MonadLogger m, Monoid w) => MonadLogger (WriterT w m)

MonadLogger m => MonadLogger (StateT s m)

MonadLogger m => MonadLogger (StateT s m)

MonadLogger m => MonadLogger (ReaderT r m)

(MonadLogger m, Error e) => MonadLogger (ErrorT e m)

MonadLogger m => MonadLogger (ContT r m)

MonadLogger m => MonadLogger (ExceptT e m)

MonadLogger m => MonadLogger (ConduitM i o m)

(MonadLogger m, Monoid w) => MonadLogger (RWST r w s m)

(MonadLogger m, Monoid w) => MonadLogger (RWST r w s m)

MonadLogger m => MonadLogger (Pipe l i o u m)

class (MonadLogger m, MonadIO m) => MonadLoggerIO m where

An extension of MonadLogger for the common case where the logging action is a simple IO action. The advantage of using this typeclass is that the logging function itself can be extracted as a first-class value, which can make it easier to manipulate monad transformer stacks, as an example.

Since 0.3.10

Minimal complete definition

Nothing

Methods

askLoggerIO :: m (Loc -> LogSource -> LogLevel -> LogStr -> IO ())

Request the logging function itself.

Since 0.3.10

Instances

MonadLoggerIO m => MonadLoggerIO (MaybeT m)

MonadLoggerIO m => MonadLoggerIO (ListT m)

MonadLoggerIO m => MonadLoggerIO (ResourceT m)

MonadLoggerIO m => MonadLoggerIO (IdentityT m)

MonadIO m => MonadLoggerIO (LoggingT m)

MonadIO m => MonadLoggerIO (NoLoggingT m)

(MonadLoggerIO m, Monoid w) => MonadLoggerIO (WriterT w m)

(MonadLoggerIO m, Monoid w) => MonadLoggerIO (WriterT w m)

MonadLoggerIO m => MonadLoggerIO (StateT s m)

MonadLoggerIO m => MonadLoggerIO (StateT s m)

MonadLoggerIO m => MonadLoggerIO (ReaderT r m)

(MonadLoggerIO m, Error e) => MonadLoggerIO (ErrorT e m)

MonadLoggerIO m => MonadLoggerIO (ContT r m)

MonadLoggerIO m => MonadLoggerIO (ExceptT e m)

MonadLoggerIO m => MonadLoggerIO (ConduitM i o m)

(MonadLoggerIO m, Monoid w) => MonadLoggerIO (RWST r w s m)

(MonadLoggerIO m, Monoid w) => MonadLoggerIO (RWST r w s m)

MonadLoggerIO m => MonadLoggerIO (Pipe l i o u m)

data LogLevel

Constructors

LevelDebug

LevelInfo

LevelWarn

LevelError

LevelOther Text

Instances

Eq LogLevel

Ord LogLevel

Read LogLevel

Show LogLevel

Lift LogLevel

type LogSource = Text

Re-export from fast-logger

data LogStr :: *

Log message builder. Use (<>) to append two LogStr in O(1).

Instances

IsString LogStr

Monoid LogStr

ToLogStr LogStr

class ToLogStr msg where

Methods

toLogStr :: msg -> LogStr

Instances

ToLogStr String

ToLogStr ByteString

ToLogStr ByteString

ToLogStr Text

ToLogStr Text

ToLogStr LogStr

Helper transformer

newtype LoggingT m a

Monad transformer that adds a new logging function.

Since 0.2.2

Constructors

LoggingT

Fields

runLoggingT :: (Loc -> LogSource -> LogLevel -> LogStr -> IO ()) -> m a

Instances

MonadTrans LoggingT

MonadTransControl LoggingT

MonadRWS r w s m => MonadRWS r w s (LoggingT m)

MonadBaseControl b m => MonadBaseControl b (LoggingT m)

MonadBase b m => MonadBase b (LoggingT m)

MonadError e m => MonadError e (LoggingT m)

MonadReader r m => MonadReader r (LoggingT m)

MonadState s m => MonadState s (LoggingT m)

MonadWriter w m => MonadWriter w (LoggingT m)

Monad m => Monad (LoggingT m)

Monad m => Functor (LoggingT m)

Monad m => Applicative (LoggingT m)

MonadActive m => MonadActive (LoggingT m)

MonadThrow m => MonadThrow (LoggingT m)

MonadCatch m => MonadCatch (LoggingT m)

MonadMask m => MonadMask (LoggingT m)

MonadIO m => MonadIO (LoggingT m)

MonadCont m => MonadCont (LoggingT m)

MonadResource m => MonadResource (LoggingT m)

MonadIO m => MonadLoggerIO (LoggingT m)

MonadIO m => MonadLogger (LoggingT m)

type StT LoggingT a = a

type StM (LoggingT m) a = StM m a

runStderrLoggingT :: MonadIO m => LoggingT m a -> m a

Run a block using a MonadLogger instance which prints to stderr.

Since 0.2.2

runStdoutLoggingT :: MonadIO m => LoggingT m a -> m a

Run a block using a MonadLogger instance which prints to stdout.

Since 0.2.2

withChannelLogger

Arguments

:: (MonadBaseControl IO m, MonadIO m)

=> Int

Number of messages to keep

-> LoggingT m a

-> LoggingT m a

Within the LoggingT monad, capture all log messages to a bounded channel of the indicated size, and only actually log them if there is an exception.

Since 0.3.2

filterLogger :: (LogSource -> LogLevel -> Bool) -> LoggingT m a -> LoggingT m a

Only log messages passing the given predicate function.

This can be a convenient way, for example, to ignore debug level messages.

Since 0.3.13

newtype NoLoggingT m a

Monad transformer that disables logging.

Since 0.2.4

Constructors

NoLoggingT

Fields

runNoLoggingT :: m a

Instances

MonadTrans NoLoggingT

MonadTransControl NoLoggingT

MonadBaseControl b m => MonadBaseControl b (NoLoggingT m)

MonadBase b m => MonadBase b (NoLoggingT m)

MonadError e m => MonadError e (NoLoggingT m)

MonadState s m => MonadState s (NoLoggingT m)

MonadWriter w m => MonadWriter w (NoLoggingT m)

Monad m => Monad (NoLoggingT m)

Monad m => Functor (NoLoggingT m)

Monad m => Applicative (NoLoggingT m)

MonadActive m => MonadActive (NoLoggingT m)

MonadThrow m => MonadThrow (NoLoggingT m)

MonadCatch m => MonadCatch (NoLoggingT m)

MonadMask m => MonadMask (NoLoggingT m)

MonadIO m => MonadIO (NoLoggingT m)

MonadResource m => MonadResource (NoLoggingT m)

MonadIO m => MonadLoggerIO (NoLoggingT m)

Monad m => MonadLogger (NoLoggingT m)

type StT NoLoggingT a = a

type StM (NoLoggingT m) a = StM m a

TH logging

logDebug :: Q Exp

Generates a function that takes a Text and logs a LevelDebug message. Usage:

$(logDebug) "This is a debug log message"

logInfo :: Q Exp

See logDebug

logWarn :: Q Exp

See logDebug

logError :: Q Exp

See logDebug

logOther :: Text -> Q Exp

Generates a function that takes a Text and logs a LevelOther message. Usage:

$(logOther "My new level") "This is a log message"

TH logging with source

logDebugS :: Q Exp

Generates a function that takes a LogSource and Text and logs a LevelDebug message. Usage:

$logDebugS "SomeSource" "This is a debug log message"

logInfoS :: Q Exp

See logDebugS

logWarnS :: Q Exp

See logDebugS

logErrorS :: Q Exp

See logDebugS

logOtherS :: Q Exp

Generates a function that takes a LogSource, a level name and a Text and logs a LevelOther message. Usage:

$logOtherS "SomeSource" "My new level" "This is a log message"

TH util

liftLoc :: Loc -> Q Exp

Lift a location into an Exp.

Since 0.3.1

Non-TH logging

logDebugN :: MonadLogger m => Text -> m ()

logInfoN :: MonadLogger m => Text -> m ()

logWarnN :: MonadLogger m => Text -> m ()

logErrorN :: MonadLogger m => Text -> m ()

logOtherN :: MonadLogger m => LogLevel -> Text -> m ()

Non-TH logging with source

logDebugNS :: MonadLogger m => Text -> Text -> m ()

logInfoNS :: MonadLogger m => Text -> Text -> m ()

logWarnNS :: MonadLogger m => Text -> Text -> m ()

logErrorNS :: MonadLogger m => Text -> Text -> m ()

logOtherNS :: MonadLogger m => Text -> LogLevel -> Text -> m ()

utilities for defining your own loggers

defaultLogStr :: Loc -> LogSource -> LogLevel -> LogStr -> LogStr

data Loc :: *

Constructors

Loc

Fields

loc_filename :: String

loc_package :: String

loc_module :: String

loc_start :: CharPos

loc_end :: CharPos

Instances

Eq Loc

Data Loc

Ord Loc

Show Loc

Generic Loc

type Rep Loc = D1 D1Loc (C1 C1_0Loc ((:*:) ((:*:) (S1 S1_0_0Loc (Rec0 String)) (S1 S1_0_1Loc (Rec0 String))) ((:*:) (S1 S1_0_2Loc (Rec0 String)) ((:*:) (S1 S1_0_3Loc (Rec0 CharPos)) (S1 S1_0_4Loc (Rec0 CharPos))))))