Re: Getting started with music functions

[Stephan Schöll]

To be precise: It's not the looping through voices which is primarly on
my mind, but rather the deduplication of code when generating scores for
each instrument.
Regards
Steff

Am 08.03.2020 um 23:57 schrieb Stephan Schöll:
> Hi all
>
> When working with larger scores / several voices/instruments, I would
> like to "loop through every single instrument" to produce the
> \book-blocks in order to avoid duplicate lilypond code.
>
> Let's take the following MVE:
> --- MVE START ---
>
> \version "2.19.83"
>
> notesI = \relative c' {
>   c4 d e f
> }
>
> notesII = \relative c {
>   e4 f g b
> }
>
> generateBook =
> #(define-music-function
>      (parser location notes)
>      (ly:music?)
>    #{
>      \book {
>        \score {
>          $notes
>          \layout {}
>        }
>      }
>    #})
>
> \generateBook \notesI
>
> \generateBook \notesII
>
> --- MVE END ---
>
> Lilypond exits with error:
> .../document.ly:24:1: error: music function cannot return ##<Book>
> \generateBook \notesI
>
> .../document.ly:26:1: error: music function cannot return ##<Book>
> \generateBook \notesII
>
> It looks as if the "output" (return value) of a function can only be of
> type "music", not "score", "book" aso, which would disappoint me. Am I
> right? Or is there a way to define/change the type of the return value?
>
> What I expect from the MVE is two PDFs, one with a notesI score, one
> with a notesII score. I have been inspired to do so by the rehearsalMidi
> function generated by Frescobaldi. I further intend to extend the music
> function with additional parameters.
>
> I'm currently on Win10 and prefer working with lilypond alone - without
> shell scripting, Python, etc.
>
> What I have already studied:
> NR, chapter 5.6 and sub-chapters
> Extending, chapter 2.3 and sub-chapters
> Urs Liskas blogposts on music functions (1-4, 2014)
>
> TIA&Regards
> Steff
>