Is gcc able to handle anonymous functions?

[Marc Hohl]

Hello list,

the topic is somewhat over my head, but perhaps someone with more insight
can answer this question?

Alternatively, I have a scheme function returning a boolean. This 
function has
to be called from inside some c++-routines, but this doesn't work yet 
(see below).

TIA,

Marc


-------- Original-Nachricht --------
Betreff: 	Re: Questions about Issue 1320: Scheme bar line interface 
(issue 6305115)
Datum:  Wed, 4 Jul 2012 06:48:56 +0200
Von:    address@hidden <address@hidden>
An:     Marc Hohl <address@hidden>



Hey Mark,

This is because, in this instance, you need to pass the function a 
pointer to a function and not a bool.  You can accomplish this through 
anonymous functions in C++11.  What'd be ideal is to create a C++ macro 
that takes a scheme function plus a number of arguments and returns a 
C++ pointer to an anonymous function.

I'll have a look in the train today and write you a more detailed 
response.  In the meantime, ask the devel list if the gcc compiler can 
handle the types of anonymous functions specified here:

http://en.wikipedia.org/wiki/Anonymous_function#C.2B.2B

All the best,
Mike

On 3 juil. 2012, at 22:17, Marc Hohl wrote:

> Hi Mike,
>
> thanks for your quick answer!
>
> Am 03.07.2012 21:13, schrieb address@hidden 
> <mailto:address@hidden>:
> > [...]
> >
> > Hey Marc,
> >
> > If the function is reused three times, you can rewrite it in Scheme. 
> >  Sorry for not having picked up on that.  You can do a module call-up 
> > as you had suggested before.
>
> I don't get it right, compilation fails
>
> note-spacing.cc: In static member function 'static Spring 
> Note_spacing::get_spacing(Grob*, Item*, Real, Real)':
> note-spacing.cc:96:72: error: no matching function for call to 
> 'Pointer_group_interface::find_grob(Item*&, SCM, bool&)'
> note-spacing.cc:96:72: note: candidate is:
> ./include/pointer-group-interface.hh:36:16: note: static Grob* 
> Pointer_group_interface::find_grob(Grob*, SCM, bool (*)(Grob*))
> ./include/pointer-group-interface.hh:36:16: note:   no known 
> conversion for argument 3 from 'bool' to 'bool (*)(Grob*)'
> make[1]: *** [out/note-spacing.o] Error 1
>
> This is how I tried to include the bar-line::non-empty-barline 
> function, defined as
>
> (define-public (bar-line::non-empty-barline grob)
>  (and (grob::has-interface grob 'bar-line)
>       (pair? (ly:grob-extent grob grob X))))
>
> diff --git a/lily/note-spacing.cc b/lily/note-spacing.cc
> index 4772367..074ad8d 100644
> --- a/lily/note-spacing.cc
> +++ b/lily/note-spacing.cc
> @@ -20,7 +20,6 @@
> #include "note-spacing.hh"
>
> #include "accidental-placement.hh"
> -#include "bar-line.hh"
> #include "directional-element-interface.hh"
> #include "grob-array.hh"
> #include "moment.hh"
> @@ -90,9 +89,11 @@ Note_spacing::get_spacing (Grob *me, Item *right_col,
>       && !skys[RIGHT].is_empty ()
>       && to_boolean (me->get_property ("space-to-barline")))
>     {
> +      bool non_empty_barline =
> +        ly_scm2bool (scm_call_1 (ly_lily_module_constant 
> ("bar-line::non-empty-barline"), right_col->self_scm ()));
>       Grob *bar = Pointer_group_interface::find_grob (right_col,
>                                                       ly_symbol2scm 
> ("elements"),
> - Bar_line::non_empty_barline);
> + non_empty_barline);
>
>       if (bar)
>         {