Re: Harp Pedals?

[Reinhold Kainhofer]

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Am Donnerstag, 14. August 2008 schrieb Valentin Villenave:
> 2007/7/8 Dewdman42 <address@hidden>:
> > I can't seem to find anything in the Lilypond manual about creating harp
> > pedal symbols.  I would think this issue has been covered a lot by users
> > of Lilypond.  how do I do it, or something like it:
> >
> > http://www.nabble.com/file/p11492013/ScreenHunter_03%2BJul.%2B08%2B12.40.
> >jpg
>
> I've been trying to implement this harp diagrams feature for a while,
> but my implementation is quite dirty and not fully working. 

Nice to see that I'm not the only one interested in implementing harp pedal 
diagrams 
(http://www.mail-archive.com/lilypond-devel%40gnu.org/msg15542.html).

> Basically, 
> I tried to write a markup command that would take seven arguments, one
> for each pedal. However, for some reason I cannot pass more than three
> arguments to the markup command (see below).
>
> 1 - What I'd really like to achieve is to have one single argument
> containing the whole set of pedals, like you do with your diagrams,
> such as
> \harp #"0;-1;0;1;0;0;1;"
> instead of
> \harp #0 #-1 #0 #1 #0 #0 #1
>
> However, I cannot parse the string to extract the values (I've tried
> to figure it out from your code, but it's way over my skills).

I'll try to come up with a proper parser.

> 2 - The implementation I provide is very dirty, as I said. [...]
> and  inside the function I don't know how I can increment the values for
> the horizontal placement of the boxes in an elegant way.

I think the easiest and most Scheme-like way would be to loop through the 
seven entries of the pedal list using recursive calls of a named let 
clause... In particular:

(let process-pedal ((remaining-pedals initial-pedals)
                            (xpos 0))
    ; print the box for the (car remaining-pedals)
    ;
    ; now call the process-pedal loop with the cdr (unless we are finished)
    ;
    (if (not (empty? (cdr remaining-pedals)))
      (process-pedal (cdr remaining-pedals) (+ xpos width-of-this-pedal))
    )
)
                           


> 3 - Ideally, we should add something like
> (if (> a 0) set! a 1
> (if (< a 0) set! a 1))
> so to allow users to use any values bigger values than 1 or lower than
> -1 without breaking their result.

Actually, each entry in a harp diagram can only have three values, so I don't 
like numeric representations too much (internally, lilypond uses integers for 
directions, but that is hidden from the user as much as possible by #UP etc. 
I don't think the users should be exposed to numbers as directions in harp 
diagrams). What I was thinking of was a rough textual representation of the 
states:
\harpPedals #"^--|v-^-" such a string with one letter per pedal is much easier 
to parse. Of course, we can have two versions, a terse one with #"^--|v-^-" 
and a "normal" one with "1;0;0;-1;0;1;0". That's just a matter of two 
different string parsers before the same function is called, similar to the 
fret-parse-definition-string function and the subsequent call to the function 
that really generates the fret diagram.

Cheers,
Reinhold

- -- 
- ------------------------------------------------------------------
Reinhold Kainhofer, Vienna University of Technology, Austria
email: address@hidden, http://reinhold.kainhofer.com/
 * Financial and Actuarial Mathematics, TU Wien, http://www.fam.tuwien.ac.at/
 * K Desktop Environment, http://www.kde.org, KOrganizer maintainer
 * Chorvereinigung "Jung-Wien", http://www.jung-wien.at/
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