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1. outputBaseThreadContext :: OutputOptions -> [Pair]

   monad-logger-aeson	Control.Monad.Logger.Aeson

   Allows for setting a "base" thread context, i.e. a set of Pair that will always be present in log messages. If we subsequently use withThreadContext to register some thread context for our messages, if any of the keys in those Pair values overlap with the "base" thread context, then the overlapped Pair values in the "base" thread context will be overridden for the duration of the action provided to withThreadContext. Default: mempty

2. outputIncludeThreadId :: OutputOptions -> Bool

   monad-logger-aeson	Control.Monad.Logger.Aeson

   Controls whether or not the thread ID is included in each log message's thread context. Default: False

3. withThreadContext :: (MonadIO m, MonadMask m) => [Pair] -> m a -> m a

   monad-logger-aeson	Control.Monad.Logger.Aeson

   This function lets us register structured, contextual info for the duration of the provided action. All messages logged within the provided action will automatically include this contextual info. This function is thread-safe, as the contextual info is scoped to the calling thread only. This function is additive: if we nest calls to it, each nested call will add to the existing thread context. In the case of overlapping keys, the nested call's Pair value(s) will win. Whenever the inner action completes, the thread context is rolled back to its value set in the enclosing action. If we wish to include the existing thread context from one thread in another thread, we must register the thread context explicitly on that other thread. myThreadContext can be leveraged in this case. Registering thread context for messages can be useful in many scenarios. One particularly apt scenario is in wai middlewares. We can generate an ID for each incoming request then include it in the thread context. Now all messages subsequently logged from our endpoint handler will automatically include that request ID:

   import Control.Monad.Logger.Aeson ((.=), withThreadContext)
   import Network.Wai (Middleware)
   import qualified Data.UUID.V4 as UUID
   
   addRequestId :: Middleware
   addRequestId app = \request sendResponse -> do
   uuid <- UUID.nextRandom
   withThreadContext ["requestId" .= uuid] do
   app request sendResponse
   

   If we're coming from a Java background, it may be helpful for us to draw parallels between this function and log4j2's ThreadContext (or perhaps log4j's MDC). They all enable the same thing: setting some thread-local info that will be automatically pulled into each logged message.

4. logItemThreadContext :: LogItem -> KeyMap Value

   monad-logger-aeson	Control.Monad.Logger.Aeson.Internal

   No documentation available.

5. loggedMessageThreadContext :: LoggedMessage -> KeyMap Value

   monad-logger-aeson	Control.Monad.Logger.Aeson.Internal

   No documentation available.

6. outputBaseThreadContext :: OutputOptions -> [Pair]

   monad-logger-aeson	Control.Monad.Logger.Aeson.Internal

   Allows for setting a "base" thread context, i.e. a set of Pair that will always be present in log messages. If we subsequently use withThreadContext to register some thread context for our messages, if any of the keys in those Pair values overlap with the "base" thread context, then the overlapped Pair values in the "base" thread context will be overridden for the duration of the action provided to withThreadContext. Default: mempty

7. outputIncludeThreadId :: OutputOptions -> Bool

   monad-logger-aeson	Control.Monad.Logger.Aeson.Internal

   Controls whether or not the thread ID is included in each log message's thread context. Default: False

8. threadContextStore :: Store (KeyMap Value)

   monad-logger-aeson	Control.Monad.Logger.Aeson.Internal

   Thread-safe, global Store that captures the thread context of messages. Note that there is a bit of somewhat unavoidable name-overloading here: this binding is called threadContextStore because it stores the thread context (i.e. ThreadContext/MDC from Java land) for messages. It also just so happens that the Store type comes from the context package, which is a package providing thread-indexed storage of arbitrary context values. Please don't hate the player!

9. class Monad m => MonadReader (m :: Type -> Type)

   monads-tf	Control.Monad.Reader

   See examples in Control.Monad.Reader. Note, the partially applied function type (->) r is a simple reader monad. See the instance declaration below.

10. mapReader :: (a -> b) -> Reader r a -> Reader r b

    monads-tf	Control.Monad.Reader

    Transform the value returned by a Reader.

    • runReader (mapReader f m) = f .
      runReader m

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