Control.Logging

This library provides a simple framework for adding logging to an application. Log configuration is passed around via implicit parameters. Each logging configuration can carry around some bit of state that can be used to annotate log lines.

Log Levels

data Level

Log Levels

Constructors

Debug

Info

Warn

Err

Crit

Instances

Enum Level

Eq Level

Ord Level

Read Level

Show Level

Log Annotations

type LogFormatter c = MaybeT (ReaderT (c, Level) IO)

The LogFormatter monad is for converting a LogAnnotation to String.

getLogLevel :: LogFormatter c Level

Returns the current log Level.

getLogContext :: LogFormatter c c

Returns the current log context.

class LogAnnotation c l where

A LogAnnotation is a typeclass to establish that an annotation can be used for logging in the log context c.

Methods

logFormat :: l -> LogFormatter c String

Instances

LogAnnotation c LAThread

LogAnnotation c LATime

LogAnnotation c LALevel

LogAnnotation c String

LogAnnotation c (LAContext c)

newtype LATime

LogAnnotation to log the current time. The String argument should provide the desired time formatting string.

Constructors

LAT String

Instances

LogAnnotation c LATime

newtype LAContext c

LogAnnotation to log a String derived from the context.

Constructors

LC (c -> String)

Instances

LogAnnotation c (LAContext c)

data LALevel

LogAnnotation to log the Level,

Constructors

LALevel

Instances

LogAnnotation c LALevel

data LAThread

LogAnnotation to log the current ThreadId

Constructors

LAThread

Instances

LogAnnotation c LAThread

data LogConfig c

Log Configuration

Constructors

LogConfig

Fields

logLevel :: Level

The minimum Level to log

logHeader :: [LogHeader c]

The list of LogHeader wrapped annotations to display on every line.

logIO :: String -> IO ()

The IO command to log a line.

logContext :: c

The user-defined context for logging.

data LogHeader c

A LogHeader wraps a LogAnnotation with existential quantifcation.

Constructors

forall l . LogAnnotation c l => LH l

Log Configuration

defaultLogConfig :: c -> LogConfig c

The default LogConfig for logging to stdout. Takes the logContext as an argument. This logs the time and Level.

fileLogConfig :: FilePath -> c -> IO (LogConfig c)

The default LogConfig that opens a file for logging.

handleLogConfig :: Handle -> c -> IO (LogConfig c)

The default LogConfig that is provided a Handle for logging.

Log Runners

type Logging c = ?log :: LogConfig c

Logging is just a Constraint synonym to denote that logging is available in a function.

runLogging :: LogConfig c -> (Logging c => a) -> a

Evaluate a value with the provided LogConfig

withLogContext :: Logging c => (c -> c) -> (Logging c => a) -> a

Evaluate a value with the log context modified by the provided function.

withLogHeader :: (Logging c, LogAnnotation c l) => l -> (Logging c => a) -> a

Evaluate a value with an additional LogAnnotation added to the header.

withLogLevel :: Logging c => Level -> (Logging c => a) -> a

Evaluate a value with the specified minimum Level.

Log Invocation

logLine :: (MonadIO m, Logging c) => Level -> String -> m ()

Write a line to the log with the specified Level.

logPrint :: (MonadIO m, Show s, Logging c) => Level -> s -> m ()

Write an instance of Show to the log with the specified Level.

debug :: (MonadIO m, Logging c) => String -> m ()

Log a line at the Debug Level.

printDebug :: (MonadIO m, Show s, Logging c) => s -> m ()

Log an instance of Show at the Debug Level.

info :: (MonadIO m, Logging c) => String -> m ()

Log a line at the Info Level.

printInfo :: (MonadIO m, Show s, Logging c) => s -> m ()

Log an instance of Show at the Info Level.

warn :: (MonadIO m, Logging c) => String -> m ()

Log a line at the Warn Level.

printWarn :: (MonadIO m, Show s, Logging c) => s -> m ()

Log an instance of Show at the Warn Level.

err :: (MonadIO m, Logging c) => String -> m ()

Log a line at the Err Level.

printErr :: (MonadIO m, Show s, Logging c) => s -> m ()

Log an instance of Show at the Err Level.

crit :: (MonadIO m, Logging c) => String -> m ()

Log a line at the Crit Level.

printCrit :: (MonadIO m, Show s, Logging c) => s -> m ()

Log an instance of Show at the Crit Level.