I've been playing with HaXmL lately. I've had a need to convert one XML document to another, and HaXmL was very nice for that. Along the way, I've discovered that I need to do some I/O as part of the conversion (specifically due to timezone-related calculations). Much of HaXML is based around the CFilter type: type CFilter = Content -> [Content] That is, most of the stuff one does in HaXML is a function with that type. Try as I might, I could not figure out a nice way to integrate I/O into this system. A simple IO CFilter wouldn't work, since there has to be input available when it runs. Content -> IO [Content] didn't work either, since the IO ripples up all the way to the top, messing up the nice code everywhere. I finally resorted to unsafePerformIO to get it done. But I'd like to know the proper solution. I do hope that this is not it :-) Thanks, John