More readable \displayMusic output.

More readable \displayMusic output.

* Omit unnecessary optional arguments.
* Use rationals when printing moments (but not with grace parts, because that's ambiguous).

It would be nice to make the pretty-printed output smarter about newlines too, e.g:

(make-music 'NoteEvent
  'duration (ly:make-duration 2)
  'pitch (ly:make-pitch 2 3))

...but the ice-9 pretty-printer isn't customizable without shipping a modified copy. I don't think it's worth the bother.

[dak, 2014-03-31 05:58:33]

https://codereview.appspot.com/82420045/diff/1/scm/music-functions.scm
File scm/music-functions.scm (right):

https://codereview.appspot.com/82420045/diff/1/scm/music-functions.scm#newcod...
scm/music-functions.scm:181: (list (ly:moment-main obj))
Two-argument form is not really ambiguous: if second argument is positive, it is
a main moment denominator, otherwise a grace.

Since obj is a constant, that can always be verified.  In the very unlikely case
of a programmatically produced positive grace time, one can still revert to the
four-argument form.

https://codereview.appspot.com/82420045/diff/1/scm/music-functions.scm#newcod...
scm/music-functions.scm:190: ,@(if-needed (ly:duration-scale obj) 1)))
This would appear to turn
(ly:make-duration 2 0 2) into (ly:make-duration 2 2).

[Devon Schudy, 2014-03-31 14:42:26]

Fix durations. Print negative graces as rationals.

[dak, 2014-03-31 15:07:34]

On 2014/03/31 14:42:26, Devon Schudy wrote:
> Fix durations. Print negative graces as rationals.

Looks good.