Re: unhandled constant?

[Han-Wen Nienhuys <hanwenn@gmail.com>]

On Sat, Feb 1, 2020 at 11:11 AM David Kastrup <dak@gnu.org> wrote:
> >> Here is an example that shows better how things work, and what might
> >> be the cause of my problems. Is it right that programmatically set
> >> contents of "current-module" are not serialized into the compiled
> >> file?
> >>
> >>    (define (run-at-compile-time cmd)
> >>      (module-define! (current-module) (string->symbol cmd) #t)
> >>      (format (current-error-port) "I-am-called-at-compile-time ~a\n" cmd))
> >>
> >>   (define (runtime-call cmd)
> >>     (format (current-error-port) "I-am-called-at-runtime ~a\n" cmd)
> >>     (format (current-error-port) "val ~a\n"
> >>             (module-ref (current-module) (string->symbol cmd))))
> >>
> >>   (defmacro foo (cmd . rest)
> >>   (run-at-compile-time cmd)
> >>   `(runtime-call ,cmd))
> >>
> >>   (foo "xy")
..
> >> ERROR: In procedure scm-error:
> >> No variable named xy in #<directory (guile-user) 56514b591140>
> >>
>
> But that is not using a local define at all.  Can you point out the
> actual code that failed for you?

There are two independent problems. One is a problem with inner
defines, which is addressed by

  https://codereview.appspot.com/553480044/

the symptom is compilation failing with "unhandled constant #<procedure ... > "

The other is a problem you can reproduce if you check out

  https://github.com/hanwen/lilypond/tree/guile22-experiment

with the symptom being:

;;; compiling /home/hanwen/vc/lilypond/out/share/lilypond/current/scm/define-markup-commands.scm
fatal error: Not a markup command: line

This is because the LilyPond macro "markup" doesn't recognize markup
command and aborts in code that is executed at compile-time. The code
that triggers this are  definitions in scm/define-markup-commands.scm
that use (mark #:blah .. ) in the function body.

You can verify this by rewriting
https://github.com/lilypond/lilypond/blob/c5ffa540fdbe52486b9575567ede70be575adb47/scm/define-markup-commands.scm#L305
and seeing how the error message changes.

I still don't understand why some code is executed compile time (the
expansion of the  markup macro) while other is not (defining the
make-x-markup function in (current-module))

Since we recognize markup commands by looking them up in
(current-module), I believe the example I showed here shows that we
can never make this work, and we  will have to revisit the markup
macros completely.

-- 
Han-Wen Nienhuys - hanwenn@gmail.com - http://www.xs4all.nl/~hanwen