Problem calling scheme code from C++

[Reinhold Kainhofer]

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I'm having serious problems calling a scheme function from C++ code. In 
particular: 

In Stem::flag (Grob *me), I have (stripped-down):
~~~~~~~~~~~~~~~~~~~~~~~~~~~
  SCM flag_style_scm = me->get_property ("flag-style");
  SCM slog = scm_int2num(log);
  SCM stc_scm = scm_call_2 (flag_style_scm,
             me->self_scm(), slog);
  return *unsmob_stencil (stc_scm);
~~~~~~~~~~~~~~~~~~~~~~~~~~~

and my .ly file is:

~~~~~~~~~~~~~~~~~~~~~~~~~~~
#(define (test-flag grob log)
  (ly:message "test-flag, grob=~a, log=~a" grob log)
  empty-stencil)

{\autoBeamOff  \override Stem #'flag-style = #test-flag
  c'8 c'16 c'32 c'64
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~


However, when I run this file, I get the error:
ERROR: In procedure test-flag:
ERROR: Wrong number of arguments to #<procedure test-flag (grob log)>

I don't understand the error, since I call the function with two arguments..
If I change the signature of test-flag to (test-flag grob . log) I see that 
log is indeed (). So, I suppose that slog is not a valid scheme object or is 
not passed to the function for some reason... Does anyone know why?

However, even if I pass some other scheme object (or use the (test-flag grob . 
log) signature), then I get the error:

ERROR: In procedure apply:
ERROR: Wrong type argument in position 1: #<Stencil  >

I also don't understand this error message and where it might come from... It 
is triggered in the scm_call_2 call, because even if I comment out the 
assertion and the unsmobbing, I get that error. Strange enough, the test-flag 
function IS executed (because the output on the command line is:
test-flag, grob=#<Grob Stem >, log=()
ERROR: In procedure apply:
ERROR: Wrong type argument in position 1: #<Stencil  >



One other thing I don't know how to do is to call a scheme function with a 
hard-coded name (e.g. I want to call the function (mensural-flag ...) with 
scm_call_2). How can I call that function explicitly from C++?

Thanks,
Reinhold
- -- 
- ------------------------------------------------------------------
Reinhold Kainhofer, Vienna University of Technology, Austria
email: address@hidden, http://reinhold.kainhofer.com/
 * Financial and Actuarial Mathematics, TU Wien, http://www.fam.tuwien.ac.at/
 * K Desktop Environment, http://www.kde.org, KOrganizer maintainer
 * Chorvereinigung "Jung-Wien", http://www.jung-wien.at/
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