Thanks, Stephen. I didn't realize I had left all those undefined's in there. I don't know of the origin of the MusicXML package. One nice thing is that reading the source for it, and looking at what fields go in the tuples, give a clue about the valid combinations of elements in MusicXML. Otherwise, I had at my disposal only some MusicXML tutorials, which don't go into depth. I supposed I could look at the XMD file or whatever that's called (the document that defines MusicXML) but I am not currently familiar with how to read those. Mike Stephen Tetley wrote:
Hi Michael
It looks fine - with one big exception.
Tracking down /undefined/ can be quite tedious, there is no indication at run time which particular undefined signalled the exit - I'd recommend you always throw an error with an identifiable string.
Also, I wonder if the the MusicXML library on Hackage was auto-generated at least in part?
It would be nicer to work with if it used constructors and field-labels more, rather than long tuples; though there isn't much you can do about that.
Best wishes
Stephen