Pew

Pew is backend agnostic structured logger. There are usage examples below

{-# LANGUAGE BlockArguments #-}
{-# LANGUAGE OverloadedStrings #-}
import Pew.Logger.Output.Json
import Pew.Logger.Implicit
import Pew.Logger.Config 
import Pew.Severity
import Data.ByteString.Builder
import System.IO

main :: IO ()
main = do
  logger <- mkJsonLogger 
    (LoggerConfig severityToText (const True)) 
    (hPutBuilder stdout)

  withLogger logger do
    logMsg Debug "kek"
    withLabel "foo" (1 :: Int) do 
      logMsg Info "lol"

Produces

{"message":"kek","timestamp":"2023-03-11T16:51:39.229087532Z","severity":"Debug","data":{}}
{"message":"lol","timestamp":"2023-03-11T16:51:39.229150711Z","severity":"Info","data":{"foo":1}}

Sometimes JSON logs aren't very convenient. For example when you are running program on local machine and you aren't able to use some json logs viewer. In such case you can use logger from Console module:

{-# LANGUAGE BlockArguments #-}
{-# LANGUAGE OverloadedStrings #-}
import Pew.Logger.Output.Console
import Pew.Logger.Implicit
import Pew.Logger.Config 
import Pew.Severity
import Data.ByteString.Builder
import System.IO

main :: IO ()
main = do
  -- you can configure colors if you want 
  logger <- mkConsoleTextLogger 
    (ConsoleLoggerConfig (const []) [] [] [] "%H:%M:%S") 
    (LoggerConfig severityToText (const True)) 
    (hPutBuilder stdout)

  withLogger logger do
    logMsg Debug "kek"
    withLabel "foo" (1 :: Int) do 
      logMsg Info "lol"

Produces

[17:01:50] [Debug] kek
[17:01:50] {#foo=1} [Info] lol