monadlog-0.1.1.1: README.md
A fast & simple logging monad
=============================
[](http://hackage.haskell.org/package/monadlog)
[](https://travis-ci.org/zmactep/monadlog)
This package is a fork of great `monad-log`, as the original author is unreachable.
It provides a mtl style `MonadLog` class and a concrete monad transformer `LogT`, the main difference between this package and monad-logger are:
+ Base monad has to be an instance of `MonadIO`.
+ Parametrized logging environment for extensibility.
+ Basic logging environment type(`Label`,`Loc`,`NameSpace`,`ThreadId`) are included, and you can easily make your own.
+ JSON logging built-in.
+ default to fast-logger backend, with good stdout and file support.
If you are an application author, you can use `LogT` transformer, a specialized reader monad to inject `Logger env`.
If you are a library author, you should:
+ make your monad stack an instance of 'MonadLog', usually you can do this by embedding `Logger env` into your monad's reader part.
+ provide a default formatter, and API to run with customized formatter.
Example
-------
+ A simple labelled logger:
```haskell
{-# LANGUAGE OverloadedStrings #-}
module Main where
import Control.Monad.Log
import Control.Monad.Log.Label
-- Following log will be output to stdout:
-- [INFO] [25-Apr-2016 12:51:56] [main] This is simple log 1
-- [INFO] [25-Apr-2016 12:51:56] [foo] This is simple log 2
main :: IO ()
main = do
logger <- makeDefaultLogger
simpleTimeFormat'
(LogStdout 4096)
levelDebug
(Label "main")
runLogTSafe logger $ do
info "This is simple log 1"
withLabel (Label "foo") $ do
info "This is simple log 2"
```
+ Logging with ThreadId:
```haskell
{-# LANGUAGE OverloadedStrings #-}
module Main where
import Control.Monad.Log
import Control.Monad.IO.Class
import Control.Monad
import Control.Concurrent
import Control.Monad.Log.LogThreadId
-- Following log will be output to stdout:
-- [INFO] [25-Apr-2016 15:06:10] [ThreadId 671] This is simple log 1
-- [INFO] [25-Apr-2016 15:06:10] [ThreadId 674] This is simple log 2
-- [INFO] [25-Apr-2016 15:06:10] [ThreadId 675] This is simple log 2
-- [INFO] [25-Apr-2016 15:06:10] [ThreadId 676] This is simple log 2
-- [INFO] [25-Apr-2016 15:06:10] [ThreadId 677] This is simple log 2
-- [INFO] [25-Apr-2016 15:06:10] [ThreadId 678] This is simple log 2
-- [INFO] [25-Apr-2016 15:06:10] [ThreadId 679] This is simple log 2
...
main :: IO ()
main = do
tid <- myLogThreadId
logger <- makeDefaultLogger
simpleTimeFormat'
(LogStdout 4096)
levelDebug
tid
runLogTSafe logger $ do
info "This is simple log 1"
replicateM_ 100 $
forkIO . runLogT' logger . withMyLogThreadId $ do
info "This is simple log 2"
```
+ Customized logging environment:
```haskell
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE FlexibleContexts #-}
module Main where
import Control.Monad.Log
import Control.Monad.Log.LogLoc
import Control.Monad.Log.NameSpace
import Data.Aeson.TH
import Data.Text (Text)
-- Following JSON log will be output to stdout:
-- {"level":"INFO","time":"25-Apr-2016 13:54:32"
-- ,"env":{"loc":{"filename":"Test.hs","module":"Test","package":"monad_GM54RwU2jZ84vGJIhnMYMH","line":33},"ns":["root"]}
-- ,"msg":"This is simple log 1"}
-- {"level":"INFO","time":"25-Apr-2016 13:54:32"
-- ,"env":{"loc":{"filename":"Test.hs","module":"Test","package":"monad_GM54RwU2jZ84vGJIhnMYMH","line":33},"ns":["foo","root"]}
-- ,"msg":"This is simple log 2"}
-- | Define your logging environment type.
-- To use 'defaultFomatter', provide a 'TextShow' instance
-- To use 'defaultJSONFomatter', provide a 'ToJSON' instance
data MyEnv = MyEnv {
loc :: LogLoc -- This is shared by every log within one 'MonadLog'.
, ns :: NameSpace
} deriving (Show, Eq)
$(deriveJSON defaultOptions ''MyEnv)
subMyNS :: (MonadLog MyEnv m) => Text -> m a -> m a
subMyNS sub = localEnv $ \env -> env { ns = pushNameSpace sub (ns env) }
main :: IO ()
main = do
logger <- makeDefaultJSONLogger
simpleTimeFormat'
(LogStdout 4096)
levelDebug
(MyEnv $myLogLoc (NameSpace ["root"]))
runLogTSafe logger $ do
info "This is simple log 1"
subMyNS "foo" $ do
info "This is simple log 2"
```