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Re: How to create a new procedure type?
Thanks, this is what I wanted to know.
Russ McManus <firstname.lastname@example.org> wrote:
> (nobody) writes:
> > This question has gone unanswered for two days, and I, too, would like
> > to know the answer. From what I grasped of Guile's pre-1.3 dynamic
> > loading support, callbacks could only take strings as args. This
> > seemed to me rather silly, since the actual arguments are of course
> > going to be Scheme objects. I guess you could sprintf(buf,"%ld",scm)
> > but you'd probably outsmart the gc by doing it.
> > Is there any way to make a C function of type SCM (*)(int nargs, SCM*
> > args) in a dynamically loaded module callable from Scheme?
> First let me say that I'm not sure that I understand your question.
> But I'll attempt an answer. Sure there is! I'll try to answer your
> question in the context of one of the examples that appear in the
> guile FAQ (http://idt.net/~mcmanus/guile-faq/guile-faq.html). Here is
> the example:
> /* $Id: hack.c,v 1.1 1999/04/14 21:18:02 mcmanr Exp $ */
> /* this code creates a new dynamically linkable module called (silly
> hack). there is precisely one primitive defined in this module,
> '2+', which adds 2 to it's argument */
> #include <guile/gh.h>
> /* add new primitives here */
> SCM_PROC(s_2_plus, "2+", 1, 0, 0, scm_2_plus);
> static SCM
> scm_2_plus(SCM x)
> SCM_ASSERT(gh_number_p(x), x, SCM_ARG1, s_2_plus);
> return(scm_sum(x, gh_int2scm(2)));
> /* the init function */
> # include "hack.x"
> /* the pre-init function */
> scm_register_module_xxx("silly hack", (void*)scm_init_hack);
> This is just about the smallest dynamically loadable C module
> possible. (You'll note that I'm not using gh_ functions, which is
> probably a bug in the FAQ, but for now, I'm just creating example the
> way I know how).
> Take the SCM_PROC line. It says that there is a new primitive
> function named "2+" from scheme, whose C implementation is the
> function scm_2_plus. You can identify the c function in error
> messages with the C constant string s_2_plus.
> The numeric argument in position three represents the number of
> required parameters. The signature of scm_2_plus should start with
> this many parameters of type SCM. These parameters will always have
> valid Scheme data when the runtime calls your function.
> The numeric argument in position four represents the number of
> optional parameters. The signature of scm_2_plus should contain, in
> addition to and following the parameters described previously, this
> many parameters. Each of these parameters may have the special value
> SCM_UNDEFINED, depending on whether the user supplied the parameter.
> The numeric argument in position five represents a C boolean
> expression that specifies whether the function accepts a 'rest' list,
> which corresponds to the dot notation in a lambda list. I will try to
> add an example of this functionality. If the parameter is true (!= 0
> in C parlance), then the signature for scm_2_plus should contain an
> additional parameter, appearing at the end of the parameter list.
> This final parameter will contain the user supplied list of additional
> arguments to the C primitive, or SCM_EOL if no list was supplied. So
> this case is the one that I think will enable you to do what you want.
> I think that there is a gh_ analog to all of this, which I need to
> research and add to the FAQ. If I'm totally off base about your
> question, my regrets.
> Death to all fanatics!
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