Re: Including only definitions from a Lilypond file

[Jérôme Plût]

> On 2020-08-14 4:48 am, David Kastrup wrote:
> > All of the elements in a score are routed through hooks you can
> > redefine.  So you can just redefine your various hooks to do nothing and
> > then include the file.
> 
> Would something like this work?
> 
> %%%%
> \version "2.20.0"
> 
> #(begin
>   (use-modules (ice-9 regex))
>   (let* ((symbols
>            (map (lambda (m) (string->symbol (match:substring m 1)))
>                 (list-matches "define ([a-z-]+-handler)"
>                   (ly:gulp-file "declarations-init.ly"))))
>          (procs (map primitive-eval symbols))
>          (null-proc (lambda args #f)))
>     (ly:parser-define! 'disableHandlers
>       (define-void-function () ()
>         (for-each
>           (lambda (sym) (primitive-eval `(set! ,sym ,null-proc)))
>           symbols)))
>     (ly:parser-define! 'restoreHandlers
>       (define-void-function () ()
>         (for-each
>           (lambda (sym proc) (primitive-eval `(set! ,sym ,proc)))
>           symbols procs)))))

This mostly works (except that I only needed to replace
"toplevel-.*-handler" functions), thanks!

Now I would like to use this to programmatically include a given file,
e.g. defining a Scheme function #(my-function "filename.ly") that would do
something equivalent to

#(compute something with "filename.ly")
\include "filename.ly"
#(compute something else with "filename.ly")

I tried to call (ly:parser-include-string (string-concatenate
`("\\disableHandlers \\include \"" ,filename "\""))) inside
my-function, but this produces
"fatal error: call-after-session used after session start".
(Some variants using ly:parser-parse-string, current-parser,
ly:parser-clone did not fare better).

Currently I see one (poor man's) way of doing that, which is calling

lilypond -e '(include "myfile.scm")' filename.ly

where "myfile.scm" does the first part of computation and sets up one
of the toplevel-.*-handler functions to do the second part of the
computation. (I've not tried it yet, though!). However this is quite
inelegant and, in particular:
 - likely not too robust w.r.t the content of "filename.ly",
 - does not allow including more than one file in sequence.

Is there a better way of doing this?

Thanks,

-- 
        Jérôme Plût