ln provides a simple interface to contextually aware structured logging. The design of ln centers around the idea of key-value pairs, which can be interpreted on the fly, but "Filters" to do things such as aggregated metrics, and report said metrics to, say Librato, or statsd. "Filters" are like WSGI, or Rack Middleware. They are run "top down" and can abort an emitted log's output at any time, or continue to let it through the chain. However, the interface is slightly different than that. Rather than encapsulating the chain with partial function application, we utilize a simpler method, namely, each plugin defines an Apply function, which takes as an argument the log event, and performs the work of the plugin, only if the Plugin "Applies" to this log event.