Re: [frogs] Changing subproperties with grob-set-property (working on bug #40)

[Marc Hohl <marc@xxxxxxxxxx>]

Neil Puttock schrieb:
> 2009/11/1 Marc Hohl <marc@xxxxxxxxxx>:
>
>   
> > Staring at the code, I get a faint impression that it would be more
> > difficult than I expected.
> > But there is a file lily/nested-property.cc. Are there some functions that
> > would do the job or
> > at least something similar to it?
> >     
>
> There's only one function in the file which will set a nested
> property.  If you're still unsure, have a look at
> new-dynamic-engraver.cc, which uses this function to set
> 'bound-details.
>   
Ah, thanks.
>   
> > At the moment, I think I understood the meaning of the arguments to
> > LY_DEFINE:
> > First comes the c++ name of the function, then the name used in scheme,
> > then the number of required arguments, the number of optional arguments,
> > then a zero (?? at least in every function I looked at), then a list of
> > arguments (...)
> > and the docstring.
> >     
>
> You're on the right track. :)
>
> The third number option sets a `rest' argument (see ly_format () for
> an example).
>   
Hm, I am not sure whether I understand that completely, but it seems
not to be important in this case.
>   
> > So the header of the definition could be
> >
> > LY_DEFINE (ly_grob_set_nested_property_x, "ly:grob-set-nested-property!",
> >      3, 0, 0, (SCM grob, SCM symlist, SCM val),
> >      "Set nested property @var{symlist} in grob @var{grob} to value
> > @var{val}.")
> > {
> >  Grob *sc = unsmob_grob (grob);
> >
> >  LY_ASSERT_SMOB (Grob, grob, 1);
> >  LY_ASSERT_TYPE (ly_is_list, symlist, 2);
> >
> > But that's more or less a guess...
> >     
>
> Looks OK, though it's preferable to use ly_cheap_is_list for
> typechecking symlist, since has a lower overhead.
>   
Ok, then:

LY_DEFINE (ly_grob_set_nested_property_x, "ly:grob-set-nested-property!",
    3, 0, 0, (SCM grob, SCM symlist, SCM val),
    "Set nested property @var{symlist} in grob @var{grob} to value
@var{val}.")
{
Grob *sc = unsmob_grob (grob);

LY_ASSERT_SMOB (Grob, grob, 1);
LY_ASSERT_TYPE (ly_cheap_is_list, symlist, 2);

if (!ly_is_procedure (val)
    && !type_check_assignment (symlist, val, ly_symbol2scm 
("backend-type?")))
  error ("typecheck failed");

set_nested_property (sc, scm_list_n (symlist, SCM_UNDEFINED), val);
return SCM_UNSPECIFIED;
}

(Hm, it still feels like the time beginning with scheme where I stirred
in the fog and put several pieces together in the hope they will work
somehow...).

Marc





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