Build Status Hackage Stackage LTS Stackage Nightly License: MIT

Auxilary logging library, which is wrapper over hslogger but allows to keep logger name into monadic context, making logging less boilerplate.

Key features:

  1. Output is colored :star:
  2. Supports logging initialization from .yaml configuration file
  3. Has wrapper for pure logging via StateT
  4. Supports log rotation
  5. Flexibles and easy setting up of loggers (using monoidal builders and lenses)
  6. Ability to acquire last N megabytes of logs from in-memory cache


This project uses universum as default prelude



  • #86: Add lens for changing properties of the particular logger.
  • Ungrade universum to the 1.0.2.


  • #79: Add launchWithConfig to Launcher module.


  • Migrate to universum-1.0.0.
  • #71: Use microlens-platform instead of lens. LoggerMap is now has field LoggerName instead of Text. zoomLogger is now work with LoggerName instead of Text. Remove LogHandler.Syslog module and network library. Remove extra, errors, exceptions, hashable, text-format, formatting dependencies. Remove loggerNameF function. Change lens to microlens-mtl in tests.


  • #75: Bump up universum lower bound.


  • #55: Return back lcFilePrefix field in LoggerConfig, rename to lcLogsDirectory.


  • Upgrade universum to version 0.9.1. Add Semigroup instances.


  • Relax containers package dependency from >= to >= Also use stable LTS for building package.


  • #55: Remove lcFilePrefix field from LoggerConfig.


  • #61: Add launchFromFile, defaultConfig and launchSimpleLogging functions.


  • #57: Add Exception module with logException and catchLog functions.
  • #60: Fix documentation for termSeveritiesOut and termSeveritiesErr.
  • #63: Timestamp rounding by powers of 10.


  • Bump containers to version 0.5.10.


  • #48: Output for severities is now configured in config file with termSeveritiesOut and termSeveritiesErr for writing into stdout and stderr accordingly. Default behavior: Errors into stderr, all other into stdout.
  • In yaml config file added new keywords for dealing with Severities: 'All' -- all severities, 'X+' -- severities greater or equal to X.
  • Changed .yaml format: logger severity receives set of severities (Severities).
  • #32: Changed .yaml format: LoggerTree should be written under 'loggerTree:'.
  • #49: Add WithLoggerIO constraint.
  • #50: Add liftLogIO function into CanLog module.


  • Error is now printed only to stderr, all other messages to stdout.
  • Logger severity is now Set Severity.
  • Interface changes: functions which worked with Severity now work with Set Severity.
  • Remove releaseAllHandlers, streamHandlerWithLock, trapLogging, debugM, errorM, infoM, noticeM, warningM.
  • Rename Wrapper module to Terminal.
  • Rename Handler module to LogHandler.
  • Rename Logger module to IOLogger.
  • Move setSeverity and setSeverityMaybe to IOLogger.
  • Lift all functions inside IOLogger module to MonadIO.
  • handle from LogHandler module is renamed to logHandlerMessage and moved out of type class LogHandler.


  • Add launchNamedPureLogWith to PureLogging
  • Improve documentation for launchNamedPureLog


  • Add logPureAction to PureLogging.
  • Add withSublogger to HasLoggerName.


  • Add usingNamedPureLogger to PureLogging.


  • Replace String to Text in LoggerName.
  • Rename LoggerName field name to getLoggerName.
  • Rename getLoggerName of HasLoggerName class to askLoggerName.
  • Use LoggerName instead of Text where possible.
  • Make separate HasLoggerName module.
  • Make separate PureLogging module.
  • Remove safecopy dependency and refactor code.


  • Add logEvents function to log [LogEvent] with proper logName.


  • Add ability to specify custom logging action.


  • Correct logger config parsing


  • Fixed a bug related to ugly output to stdout even when it was turned off.


  • Minor dependencies update.


  • Fix minor bug with stdout severity.


  • Allow to use arbitrary text formatter function.


  • Add ability to specify time format for logs.
  • Some space leaks elimination: + The MemoryQueue has been partially reworked to get rid of the "inline" State manipulation; + Strings have been dropped almost everywhere in favour of Text; + A LogFormatter has been reworked to yield a IO Builder; + replaceVarM has been reworked to be pure and to work with builders rather than plain Text/Strings; + The pure logger has been reworked to use strict's StateT instead of WriterT; + The pure logger have been polished to drop instances which required the UndecidableInstances pragma; + The Sized instance for Text has been reworked and multiplied by a constant factor of 16 (see below).


  • Now we create a directory for log files if it's missing.


  • Fixed memory leak (PR #17).


  • Supports Unix paths in log configs even on Windows.


  • Uses universum-0.6.1.


  • Add CanLog and HasLoggerName instances for both strict and lazy State.


  • Add config parameter to print ThreadId optionally.
  • Boolean monoidal builders for LoggerConfig now set boolean parameter to default ≠ mempty parameter.
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