Safe Haskell	Trustworthy
Language	Haskell98

Control.Monad.Logger

Contents

MonadLogger
Re-export from fast-logger
Helper transformer
TH logging
TH logging of showable values
TH logging with source
TH util
Non-TH logging
Non-TH logging with source
utilities for defining your own loggers

Description

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.

Synopsis

MonadLogger

class Monad m => MonadLogger m where Source

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 () Source

Instances

MonadLogger m => MonadLogger (MaybeT m) Source
MonadLogger m => MonadLogger (ListT m) Source
MonadLogger m => MonadLogger (ResourceT m) Source
MonadLogger m => MonadLogger (IdentityT m) Source
MonadIO m => MonadLogger (LoggingT m) Source
Monad m => MonadLogger (NoLoggingT m) Source
(MonadLogger m, Monoid w) => MonadLogger (WriterT w m) Source
(MonadLogger m, Monoid w) => MonadLogger (WriterT w m) Source
MonadLogger m => MonadLogger (StateT s m) Source
MonadLogger m => MonadLogger (StateT s m) Source
MonadLogger m => MonadLogger (ReaderT r m) Source
(MonadLogger m, Error e) => MonadLogger (ErrorT e m) Source
MonadLogger m => MonadLogger (ContT r m) Source
MonadLogger m => MonadLogger (ExceptT e m) Source
MonadLogger m => MonadLogger (ConduitM i o m) Source
(MonadLogger m, Monoid w) => MonadLogger (RWST r w s m) Source
(MonadLogger m, Monoid w) => MonadLogger (RWST r w s m) Source
MonadLogger m => MonadLogger (Pipe l i o u m) Source

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

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 ()) Source

Request the logging function itself.

Since 0.3.10

Instances

MonadLoggerIO m => MonadLoggerIO (MaybeT m) Source
MonadLoggerIO m => MonadLoggerIO (ListT m) Source
MonadLoggerIO m => MonadLoggerIO (ResourceT m) Source
MonadLoggerIO m => MonadLoggerIO (IdentityT m) Source
MonadIO m => MonadLoggerIO (LoggingT m) Source
MonadIO m => MonadLoggerIO (NoLoggingT m) Source
(MonadLoggerIO m, Monoid w) => MonadLoggerIO (WriterT w m) Source
(MonadLoggerIO m, Monoid w) => MonadLoggerIO (WriterT w m) Source
MonadLoggerIO m => MonadLoggerIO (StateT s m) Source
MonadLoggerIO m => MonadLoggerIO (StateT s m) Source
MonadLoggerIO m => MonadLoggerIO (ReaderT r m) Source
(MonadLoggerIO m, Error e) => MonadLoggerIO (ErrorT e m) Source
MonadLoggerIO m => MonadLoggerIO (ContT r m) Source
MonadLoggerIO m => MonadLoggerIO (ExceptT e m) Source
MonadLoggerIO m => MonadLoggerIO (ConduitM i o m) Source
(MonadLoggerIO m, Monoid w) => MonadLoggerIO (RWST r w s m) Source
(MonadLoggerIO m, Monoid w) => MonadLoggerIO (RWST r w s m) Source
MonadLoggerIO m => MonadLoggerIO (Pipe l i o u m) Source

data LogLevel Source

Constructors

LevelDebug
LevelInfo
LevelWarn
LevelError
LevelOther Text

Instances

Eq LogLevel Source
Ord LogLevel Source
Read LogLevel Source
Show LogLevel Source
Lift LogLevel Source

type LogSource = Text Source

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 Source

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 Source
MonadTransControl LoggingT Source
MonadRWS r w s m => MonadRWS r w s (LoggingT m) Source
MonadBaseControl b m => MonadBaseControl b (LoggingT m) Source
MonadBase b m => MonadBase b (LoggingT m) Source
MonadError e m => MonadError e (LoggingT m) Source
MonadReader r m => MonadReader r (LoggingT m) Source
MonadState s m => MonadState s (LoggingT m) Source
MonadWriter w m => MonadWriter w (LoggingT m) Source
Monad m => Monad (LoggingT m) Source
Monad m => Functor (LoggingT m) Source
Monad m => Applicative (LoggingT m) Source
MonadActive m => MonadActive (LoggingT m) Source
MonadThrow m => MonadThrow (LoggingT m) Source
MonadCatch m => MonadCatch (LoggingT m) Source
MonadMask m => MonadMask (LoggingT m) Source
MonadIO m => MonadIO (LoggingT m) Source
MonadCont m => MonadCont (LoggingT m) Source
MonadResource m => MonadResource (LoggingT m) Source
MonadIO m => MonadLoggerIO (LoggingT m) Source
MonadIO m => MonadLogger (LoggingT m) Source
type StT LoggingT a = a Source
type StM (LoggingT m) a = StM m a Source

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

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

Since 0.2.2

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

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

Since 0.2.2

runChanLoggingT :: MonadIO m => Chan (Loc, LogSource, LogLevel, LogStr) -> LoggingT m a -> m a Source

Run a block using a MonadLogger instance which writes tuples to an unbounded channel.

The tuples can be extracted (ie. in another thread) with unChanLoggingT or a custom extraction funtion, and written to a destination.

Since: 0.3.17

unChanLoggingT :: (MonadLogger m, MonadIO m) => Chan (Loc, LogSource, LogLevel, LogStr) -> m () Source

Read logging tuples from an unbounded channel and log them into a MonadLoggerIO monad, forever.

For use in a dedicated thread with a channel fed by runChanLoggingT.

Since: 0.3.17

withChannelLogger Source

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 Source

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 Source

Monad transformer that disables logging.

Since 0.2.4

Constructors

NoLoggingT
Fields runNoLoggingT :: m a

Instances

MonadTrans NoLoggingT Source
MonadTransControl NoLoggingT Source
MonadBaseControl b m => MonadBaseControl b (NoLoggingT m) Source
MonadBase b m => MonadBase b (NoLoggingT m) Source
MonadError e m => MonadError e (NoLoggingT m) Source
MonadState s m => MonadState s (NoLoggingT m) Source
MonadWriter w m => MonadWriter w (NoLoggingT m) Source
Monad m => Monad (NoLoggingT m) Source
Monad m => Functor (NoLoggingT m) Source
Monad m => Applicative (NoLoggingT m) Source
MonadActive m => MonadActive (NoLoggingT m) Source
MonadThrow m => MonadThrow (NoLoggingT m) Source
MonadCatch m => MonadCatch (NoLoggingT m) Source
MonadMask m => MonadMask (NoLoggingT m) Source
MonadIO m => MonadIO (NoLoggingT m) Source
MonadResource m => MonadResource (NoLoggingT m) Source
MonadIO m => MonadLoggerIO (NoLoggingT m) Source
Monad m => MonadLogger (NoLoggingT m) Source
type StT NoLoggingT a = a Source
type StM (NoLoggingT m) a = StM m a Source

TH logging

logDebug :: Q Exp Source

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

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

logInfo :: Q Exp Source

See logDebug

logWarn :: Q Exp Source

See logDebug

logError :: Q Exp Source

See logDebug

logOther :: Text -> Q Exp Source

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

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

TH logging of showable values

logDebugSH :: Q Exp Source

Generates a function that takes a 'Show a => a' and logs a LevelDebug message. Usage:

$(logDebugSH) (Just "This is a debug log message")

Since: 0.3.18

logInfoSH :: Q Exp Source

See logDebugSH

logWarnSH :: Q Exp Source

See logDebugSH

logErrorSH :: Q Exp Source

See logDebugSH

logOtherSH :: Text -> Q Exp Source

Generates a function that takes a 'Show a => a' and logs a LevelOther message. Usage:

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

TH logging with source

logDebugS :: Q Exp Source

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 Source

See logDebugS

logWarnS :: Q Exp Source

See logDebugS

logErrorS :: Q Exp Source

See logDebugS

logOtherS :: Q Exp Source

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 Source

Lift a location into an Exp.

Since 0.3.1

Non-TH logging

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

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

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

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

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

Non-TH logging with source

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

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

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

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

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

utilities for defining your own loggers

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

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))))))