Policy that determines how the case of a congested logging pipeline is addressed.

The Internal log message type.

The type parameter a is expected to provide intances of Show, Typeable, and NFData.

If we need to support different backends, we may consider including the backend here...

This is given to logger when it is created. It formats and delivers individual log messages synchronously. The backend is called once for each log message (that meets the required log level).

The type parameter a is expected to provide instances for Show Typeable, and NFData.

The Left values of the argument allows the generation of log messages that are independent of the parameter a. The motivation for this is reporting issues in Logging system itself, like a full logger queue or providing statistics about the fill level of the queue. There may be other uses of this, too.

Backends that can fail are encouraged (but not forced) to take into account the LogPolicy that is effective for a message. For instance, a backend may implement a reasonable retry logic for each message and then raise a BackendTerminatedException in case the policy is LogPolicyBlock or LogPolicyRaise (thus causing the logger to exit immediately) and raise some other exception otherwise (thus discarding the message without causing the logger to not exit immediately). In addition a backend might retry harder in case of LogPolicyBlock.

TODO there may be scenarios where chunked processing is beneficial. While this can be done in a closure of this function, more direct support might be desirable.

This function is provided by the logger.

Abstraction of a logger context that can be used without dependening on a specific monadic context.

The loggerFunIO incorporates a LoggerBackend. An instance of a LoggerCtx is free to use a hard coded LoggerBackend or to be usable with different LoggerBackend functions. The latter is recommended but not required.

You don't have to provide an instance of this for your logger. Instead you may just provide an instance of MonadLog directly.

If this doesn't fit your needs you may use a newtype wrapper and define your own instances.