Hi, We were discussing how to consume the eventlog incrementally on #ghc today. Would it be feasible to offer an API (e.g. GHC.EventLog) that allows programs to register for events that occur in the program? Programs would register listeners like so: registerEventListener (\ event -> doSomethingWith event) The current write-to-file system could be implemented in terms of this API. We could even allow event logging to be turned on/off from within the application, allowing developers to attach to a running application, enable event logging, diagnose the app, and then turn of event logging again. The RTS would invoke listeners every time a new event is written. This design has many benefits: - We don't need to introduce the serialization, deserialization, and I/O overhead of first writing the eventlog to file and then parsing it again. - Programs could monitor themselves and provide debug output (e.g. via some UI component). - Users could write code that redirects the output elsewhere e.g. to a socket for remote monitoring. Would invoking a callback on each event add too big of an overhead? How about invoking the callback once every time the event buffer is full? Johan