Control.Monad.Logger.Prefix

This module exports the LogPrefixT monad transfomer. This transformer adds a given prefix to a MonadLogger context, allowing you to make your logs a bit more greppable without including much boilerplate. The prefixes can be nested easily.

The function prefixLogs is the most convenient way to use the library. All you have to do is use the function to add the prefix, and it Just Works. Here's an example:

someLoggingFunction :: MonadLogger m => m ()
someLoggingFunction = do
    $(logDebug) "No prefix here"
    "foo" `prefixLogs` do
        $(logDebug) "There's a [foo] there!
        "bar" `prefixLogs` do
            $(logDebug) "Now there's a [foo] *and* a [bar]"

LogPrefixT

data LogPrefixT m a

LogPrefixT is a monad transformer that prepends a bit of text to each logging action in the current MonadLogger context. The internals are currently implemented as a wrapper around ReaderT LogStr.

Instances

MonadTrans LogPrefixT

Defined in Control.Monad.Logger.Prefix

Methods

lift :: Monad m => m a -> LogPrefixT m a

MonadBase b m => MonadBase b (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

liftBase :: b α -> LogPrefixT m α

MonadBaseControl b m => MonadBaseControl b (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Associated Types

type StM (LogPrefixT m) a :: Type

Methods

liftBaseWith :: (RunInBase (LogPrefixT m) b -> b a) -> LogPrefixT m a

restoreM :: StM (LogPrefixT m) a -> LogPrefixT m a

MonadWriter w m => MonadWriter w (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

writer :: (a, w) -> LogPrefixT m a

tell :: w -> LogPrefixT m ()

listen :: LogPrefixT m a -> LogPrefixT m (a, w)

pass :: LogPrefixT m (a, w -> w) -> LogPrefixT m a

MonadState s m => MonadState s (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

get :: LogPrefixT m s

put :: s -> LogPrefixT m ()

state :: (s -> (a, s)) -> LogPrefixT m a

MonadReader r m => MonadReader r (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

ask :: LogPrefixT m r

local :: (r -> r) -> LogPrefixT m a -> LogPrefixT m a

reader :: (r -> a) -> LogPrefixT m a

MonadError e m => MonadError e (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

throwError :: e -> LogPrefixT m a

catchError :: LogPrefixT m a -> (e -> LogPrefixT m a) -> LogPrefixT m a

Monad m => Monad (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

(>>=) :: LogPrefixT m a -> (a -> LogPrefixT m b) -> LogPrefixT m b

(>>) :: LogPrefixT m a -> LogPrefixT m b -> LogPrefixT m b

return :: a -> LogPrefixT m a

fail :: String -> LogPrefixT m a

Functor m => Functor (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

fmap :: (a -> b) -> LogPrefixT m a -> LogPrefixT m b

(<$) :: a -> LogPrefixT m b -> LogPrefixT m a

Applicative m => Applicative (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

pure :: a -> LogPrefixT m a

(<*>) :: LogPrefixT m (a -> b) -> LogPrefixT m a -> LogPrefixT m b

liftA2 :: (a -> b -> c) -> LogPrefixT m a -> LogPrefixT m b -> LogPrefixT m c

(*>) :: LogPrefixT m a -> LogPrefixT m b -> LogPrefixT m b

(<*) :: LogPrefixT m a -> LogPrefixT m b -> LogPrefixT m a

MonadIO m => MonadIO (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

liftIO :: IO a -> LogPrefixT m a

MonadResource m => MonadResource (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

liftResourceT :: ResourceT IO a -> LogPrefixT m a

MonadThrow m => MonadThrow (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

throwM :: Exception e => e -> LogPrefixT m a

MonadCatch m => MonadCatch (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

catch :: Exception e => LogPrefixT m a -> (e -> LogPrefixT m a) -> LogPrefixT m a

MonadMask m => MonadMask (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

mask :: ((forall a. LogPrefixT m a -> LogPrefixT m a) -> LogPrefixT m b) -> LogPrefixT m b

uninterruptibleMask :: ((forall a. LogPrefixT m a -> LogPrefixT m a) -> LogPrefixT m b) -> LogPrefixT m b

generalBracket :: LogPrefixT m a -> (a -> ExitCase b -> LogPrefixT m c) -> (a -> LogPrefixT m b) -> LogPrefixT m (b, c)

MonadLogger m => MonadLogger (LogPrefixT m)

Defined in Control.Monad.Logger.Prefix

Methods

monadLoggerLog :: ToLogStr msg => Loc -> LogSource -> LogLevel -> msg -> LogPrefixT m ()

type StM (LogPrefixT m) a

Defined in Control.Monad.Logger.Prefix

type StM (LogPrefixT m) a = StM m a

prefixLogs :: Text -> LogPrefixT m a -> m a infixr 5

This function runs the underlying MonadLogger instance with a prefix using the LogPrefixT transformer.

>>> :set -XOverloadedStrings
>>> let l = logDebugN "bar"
>>> runStdoutLoggingT (prefixLogs "foo" (logDebugN "bar\n"))
[Debug] [foo] bar
...

module Control.Monad.Logger