Here is how I see the possible evolutions of the program. If you are interested , contact me, I can privilege the development of the part you prefer.
That's done.
Midi file generation is an excellent medium in order to work this exercices with a Midi engine, without reading anything, at different tempi. I found tclmidi. It is a very good tool. I won't make one.
Nice scores in LaTeX, DVI, PostScript formats (A4, Letter, ...). Lilypond sounds very good.
Further variations. Accents are excellent to fix stroke control.
Here, more work in view, for me and for drummers. A code remodelling is needed. The opportunity to switch towards an object oriented architecture.
A complete rewriting in an Java applet would be saving for the server's ressources. There is also Python (Is Grail still so low ?), and PerlTk (easier because in PerlTk there is Perl and Tk)