music variables and music templates - an idea

[Jan-Peter Voigt]

Hello list,

I created some functions  to store music in a hierarchical tree. This 
"music store" leads to the possibility to store music in one place and 
to get voices/parts in a defined template.
If you have to put several choral pieces in one book, you can first fill 
all voices in this tree with a structure <piece>/notes/[sop|alt|ten|bas] 
and then later refer to that music in a common SATB-template. If your 
book shall have another look for all choral pieces, you only have to 
change the template. And if you want to combine several pieces in one 
bookpart, you can first \include all music definitions, then display the 
music where you like to.

In this example file, I inserted one choral piece (SATB), wich is first 
displayed in a four-stave-four-lyric-system, then in a 
two-stave-one-lyric-system.

In the underlying tree, wich is an alist, you can access values by path, 
wich is a list of symbols - for example (tree-get tree '(path to value))
One value can be stored in path '()
Like with assoc-set!, the actual tree is not modified, but the modified 
is returned.
These tree-functions are used in the get/put-music-functions, wich are 
actually defined in a closure.

If I typeset pieces, I use a modified include-function, wich only 
includes, if the outname equals the location-name. This way I can 
"\includeLocal" a testfile, wich instantiates the current piece (wich is 
set before) only if I am working on that specific file:
--snip--
#(define-public includeLocal (define-music-function (parser location 
file)(string?)
    (let ((outname (format "~A.ly" (ly:parser-output-name parser)))
          (locname (car (ly:input-file-line-char-column location))))
         (if (string=? outname locname)
             (let ((content (ly:gulp-file file)))
                  (ly:parser-include-string parser content)))
         (make-music 'SequentialMusic 'void #t))))
--snip--

I know, this is another way to handle this 
multi-score-in-one-book-thing. But perhaps it includes at least some 
useful ideas.
If this is of interest, I'd like to get respond and suggestions to 
improve it.

Cheers,
Jan-Peter

template-mechanics.ly
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