Re: My own wishlist...

[Nicolas Sceaux]

Tue, 3 Feb 2004 15:58:07 +0100, Han-Wen a dit : 

 > address@hidden writes:
 >> A cheap functionality, which would prove very useful in
 >> practice, would be the ability to declare Lilypond stuff
 >> in scheme, as in:
 >> 
 >> (map myfunc {\notes { a b c d | a b c d}})
 >> 
 >> which would be equivalent to:
 >> 
 >> tempvar0981 = \notes { a b c d | a b c d}
 >> 
 >> (map myfunc tempvar0981)
 >> 
 >> Since we already have the ability to declare 
 >> Scheme stuff within LilyPond, allowing for the
 >> reverse might be enough for most applications....
 >> 
 >> Is this just nonsense, or is this reasonable to implement
 >> (I don't know whether one can plug language extensions in
 >> GUILE...) ?

 > I don't know how it can be done. Perhaps our Scheme macro expert can
 > chip in some ideas. Nicolas?

sorry for the delay, I was not at home.

What is easy, is to write a set of scheme operators that would reflect
common LilyPond commands, for instance: 

  (context-property-override Voice Stem thickness 2.0)
  ==> \property Voice.Stem \override #'thickness = #2.0

or: (skip "1.*4/3") ==> s1.*4/3
etc.

Actually, I have started to build such a library on a per need basis
for my scores. I am considering contributing a complete set of these
scheme operators, aiming at programatically building any music
expressions.

As for reading a lilypond expression in scheme, it is not trivial. I
once tried to hack my lilypond-program so that the lilypond-language
compiler could be called within scheme via a call to a C function in a
lily shared library, without real success. I didn't know enough of
lilypond internals. It is feasible, however, but when I discovered
what the \apply command could do, I definitely got rid of the idea of
using lilypond expression in scheme. \apply is enough -- if you don't
have to call a function with several music arguments. Some kind of
multi-arguments apply would be cool.

  \apply-3 #bass-part
  { ...bass notes... }
  { ...figures... }

 > In the meantime, you can achieve the same thing  with apply, albeit a
 > little more verbose

 > \apply #(lambda (m)
 >   ..more stuff.. )
 >   \notes { a b c d | a b c d}

What could be also usefull is some specialized mapping functions:

  \apply #(lambda (music)
            (map-if mus:note? 
                    (lambda (note) (..do something on a note..))
                    music))
  \notes { a b c d | a b c d}

where `map-if' would look deeply into `music', and for each element
satisfying the predicate (eg. `mus:note?') would apply the function
on it.
Oh, this is not very beautiful for a LilyPond score... macrology may
help:

  \apply #(with-note-mapping (note)
            (..do something on a note..))
  \notes { a b c d | a b c d}

etc.

nicolas