Incrementally consuming the eventlog

Don Stewart dons00 at
Sun May 1 19:22:29 CEST 2011

I've put a library for incremental parsing of the event log here:

The goal is to implement something like:

On Sun, May 1, 2011 at 1:44 AM, Johan Tibell <johan.tibell at> wrote:
> On Fri, Apr 29, 2011 at 12:00 AM, Don Stewart <dons00 at> wrote:
>> I'm very interested in what the best way to get incremental event data
>> from a running GHC process would be.
>> Looking at the code, we flush the event buffer fairly regularly, but
>> the event parser is currently strict.
>> So we'd need a lazy (or incremental) parser, that'll return a list of
>> successful event parses, then block. I suspect this mode would be
>> supported.
>> *My evil plan is to write a little monitoring web app that just
>> attaches to the event stream and renders it in a useful "heartbeat"
>> format* , but I need incremental parsing.
> A less general solution might be to have the program itself start a
> little web server on some port and use the API I proposed to serve
> JSON data with the aggregate statistics you care about. Example:
>    main = do
>      eventData <- newIORef
>      server <- serveOn 8080 $ \ _req -> readIORef eventData >>=
> sendResponse eventData
>      registerEventListener $ \ ev -> updateEventData eventData ev
>      runNormalProgram
> You can wrap the creation of the webserver in a little helper function
> an make any program "monitorable" simply by doing
>    main = withMonitoring runApp
> withMonitoring would take care of starting/stopping the webserver and
> processing events.
> Just a thought.
> Johan

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