harp-pedal code

[Carl D. Sorensen]

Reinhold,

I've been reviewing the harp-pedal code in order to change the circles to
ellipses.

I found a couple of things that I'd like to comment on.

1.  The verbose interface that I had in mind would be significantly
different than the verbose interface you have. In fret diagrams, the verbose
interface has a list of sub-lists, with each sub-list indicating an item to
place on the fret diagram.  So instead of a list like you have here, which
is a list replacement for a string (no extra information about what the
meaning of each element is), you might have each element of the harp-pedal
list be an entry like

(item-type x-position y-position circled?),

where

item-type could be 'pedal or 'divider,
x-position is the x-position of the object,
y-position is the y-position of the object, and
circled? tells whether the item is circled or not.

This makes for a _very_ awkward user interface, because pedal-list looks
like:

(list
  ('pedal 1 UP #t)
  ('pedal 2 CENTER #f)
  ('pedal 3 DOWN #t)
  ('divider 3.5 CENTER #f)
  ('pedal 4 CENTER #f)
  ('pedal 5 CENTER #f)
  ('pedal 6 CENTER #f)
  ('pedal 7 CENTER #f))

But it also makes for a very nice program interface, because the order of
pedal-list no longer matters, and each item on the list can be drawn
independently.

I'm not advocating that you do this for harp-pedals, but this is the style
of interface that Han-Wen asked me to put on fret-diagrams, and it was quite
useful in the automatically calculated fret-diagram code.  It may be useful
for other kinds of instrument notation, and I wanted to get it into the
-devel archives.


2.  I note that you redefine circle-stencil in make-harp-pedal:

(let* ((...
       (circle-stencil (if circled (circle-stencil stencil ....))

The first circle-stencil is going to be a circled pedal.  The second is the
procedure that draws a circle around the pedal.  While this works in Scheme,
I don't think it's good practice.  It would be better, IMO, to change the
first one from circle-stencil to something like pedal-stencil.

3.  I like your code overall -- it's a very nice job!

Carl