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
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