[CM] Parsing MIDI files with CM

[Rick Taube]

> It used to be possible with map-subobjects, using the :type keyword,
> but this function seems to have disappeared although still somewhat
> documented in the dictionary.

hi -- it got renamed map-objects because it can also map lists of 
objects as well as containers. It has a :class keyword if you want to 
only map a certain typ of objects. There is a fold-objects function 
that you can use to return lists (and other things) from mapping.

given

	(defparameter s1 (import-events "/Lisp/cm/etc/tutorials/source.mid" ))

then to return all the keynum slot values of just MIDI objects in s1:

	(fold-objects (lambda (x l) (cons x l)) s1 '() :slot 'keynum :class 
'midi)

	=> (77 77 77 89 75 86 74 92 87 80 ...)

to collect lists of things, you map the objects rather than a slot and 
return what you want:

	(fold-objects (lambda (x l) (cons (list (sv x :time) (sv x :keynum)) 
l)) s1 '() :class 'midi)

	=> ((18.0 77) (17.875 77) (17.75 77) (17.75 89) (17.625 75) (17.625 
86) ...)


for more information see:

http://commonmusic.sourceforge.net/etc/tutorials/editing.lisp

and

http://commonmusic.sourceforge.net/doc/dict/fold-objects-fn.html