Comment #6 on issue 2491 by [email protected]: Patch: Macro for(UP_and_DOWN) and 3 similar.
http://code.google.com/p/lilypond/issues/detail?id=2491
heh, that's how it goes.If you haven't done so already, is it possible to submit a patch which only adds the macro (and does not touch the buggy loop) ? If the macro-only change works, let's get that pushed, and _then_ look at the buggy loop in isolation.
