monad-logger-extras: Utilities for composing loggers, coloring output, plus a few orphan instances.

[ bsd3, library, program, system ] [ Propose Tags ]

Build composable logging backends for monad-logger. This package includes a few composable backends (including a posix syslog backend) and some extras like log output coloring utilities.

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Dependencies ansi-terminal (>=0.9 && <0.12), base (>=4.12 && <5), bytestring (>=0.10 && <0.12), hsyslog (>=5 && <5.1), monad-logger (>=0.3.36 && <0.4), monad-logger-extras, mtl (>=2.2 && <2.3) [details]
License BSD-3-Clause
Copyright 2020 Obsidian Systems LLC
Author Obsidian Systems LLC
Category System
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Source repo head: git clone git://
Uploaded by abrar at 2020-12-01T15:09:08Z
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Reverse Dependencies 2 direct, 2 indirect [details]
Executables readme
Downloads 627 total (16 in the last 30 days)
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Readme for monad-logger-extras-

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Composable logging, syslog integration, and more with monad-logger.


This package provides a way to compose logging actions so that you can conveniently log to multiple destinations. It also includes implementations of a few common logging actions: logging to stdout, stderr, nowhere (similar to NoLoggingT), and to a posix syslog (using hsyslog).

Logs can be emitted in color by using the colorize or colorizeWith function on your Logger.

This package also contains a couple of orphan instances for LoggingT: MonadPlus and Alternative.

Example usage

Watch for the system log message by running:

journalctl --user -t log-test -f

This example can be built and run using cabal (either cabal repl example or cabal build example).

> {-# LANGUAGE OverloadedStrings #-}
> import Control.Monad.Logger
> import Control.Monad.Logger.Extras
> main :: IO ()
> main = do
>   let logger = colorize logToStdout <> logToStderr <> logToSyslog "log-test"
>   flip runLoggerLoggingT logger $ do
>     logInfoN "This is a test. You should see this on stdout, stderr, and in your system log."
>     logDebugN "This is a debug message."
>     logWarnN "This is a warning."
>     logErrorN "This is an error!"

This should produce output that looks like this (note that the stdout log has been colorized):

Example output