Re: Harp Pedals?

[Valentin Villenave]

2008/8/14 Carl D. Sorensen <address@hidden>:

> Valentin, you made my day.  To have somebody asking _me_ questions
> about LilyPond programming is a first.  I've been the one asking
> everybody else questions.  Thanks!

Well, had I known it would make your day, I'd have spent less time
looking at your code and asked my question sooner :-)

> You really don't want to get in the string business for this case.

> It's much easier to just pass one argument to the function, a
> list of pedal values.

Oh yeah! Stupid, stupid me. I simply forgot about the list type.

> If you really want to do this (why would users want to have values
> greater than 1 or less than -1?  I don't know harp music, so I can't say),

You have a point. However, what Reinhold proposes is even sexier (see below).

> This requires you to use lambda expressions, which are kind of confusing.

Are lambda expressions related to http://en.wikipedia.org/wiki/Lambda_calculus?

If so, I have to confess I kinda gave up every time I tried to read
the Wikipedia page... :(

> If you're going to do scheme programming with lilypond, lambda functions
> are your friends, even though they can be confusing.

I'll try harder then...


> At the time I wrote fret-diagrams, constants like 4, 2, and 0.4
> were frowned upon.  So I used variables connected to properties
> every time I needed a constant like this, and there was concern about
> polluting the property name space, so I created fret-diagram-details.

Yes indeed.

> Also, LilyPond coding standards call for using full words rather than
> abbreviations for variable names.  x, y, a, b and so forth should only
> be used as part of a lambda function definition.

Actually, d c b and so on referred to the note of the pedals.

> With make-pedal-stencil defined you can now add a new variable to your let
> assignment list
[...]
> And before your code to add stencils you can do a for-each:
[...]
> Which should glue all of your pedal stencils together in one big
> stencil pedals-stencil.

Great! This definitely looks good.

> I think it's good for you to figure out how it works, so I've left the
> debugging to you.  If you have more questions, feel free to ask.

I guess I will, pretty soon :)

Many thanks anyway.

2008/8/14 Reinhold Kainhofer <address@hidden>:

> 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).

Oh yes, I remember now that you had asked for possible glyphs.

> 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:

The problem is that the pedal boxes are not evenly spaced (there are
three on one side, four on the other).

> 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.

This is just awesome! Can it be handled by pure Scheme though, or does
this need to be dealt with on the C++ side?

> 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.

This looks really, really cool, though way beyond my knowledge. Nice
to have some "real" people on my side, anyway :-)

Cheers,
Valentin