From: Alex Vong <alexvong1995@gmail.com>
To: Pierre LINDENBAUM <Pierre.Lindenbaum@univ-nantes.fr>
Cc: guile-user@gnu.org
Subject: Re: function registered with scm_c_define_gsubr: how can i handle an optional parameter?
Date: Thu, 14 Dec 2017 18:19:11 +0800 [thread overview]
Message-ID: <877etpwr1c.fsf@gmail.com> (raw)
In-Reply-To: <caddca02bf50a5514afd592351d01bbe@imap.univ-nantes.prive> (Pierre LINDENBAUM's message of "Wed, 13 Dec 2017 22:50:17 +0100")
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Hello,
From the Guile manual ``6.1 Overview of the Guile API'',
> For some Scheme functions, some last arguments are optional; the
> corresponding C function must always be invoked with all optional
> arguments specified. To get the effect as if an argument has not been
> specified, pass ‘SCM_UNDEFINED’ as its value. You can not do this for
> an argument in the middle; when one argument is ‘SCM_UNDEFINED’ all the
> ones following it must be ‘SCM_UNDEFINED’ as well.
Therefore, we can check if opt_arg2 has the value SCM_UNDEFINED, to
decide if we have received an optional argument. The code is in the
attachment:
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#include <libguile.h>
static SCM myfun(SCM arg1,SCM opt_arg2)
{
if (opt_arg2 == SCM_UNDEFINED)
scm_display(scm_from_utf8_string("Optional argument NOT received!\n"),
scm_current_output_port());
else
scm_display(scm_from_utf8_string("Optional argument received!\n"),
scm_current_output_port());
return SCM_BOOL_T;
}
void
init_myfun(void)
{
scm_c_define_gsubr("myfun", 1, 1, 0, myfun);
}
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Cheers,
Alex
Pierre LINDENBAUM <Pierre.Lindenbaum@univ-nantes.fr> writes:
> Hi all,
>
> (cross posted on SO: https://stackoverflow.com/questions/47797521 )
>
>
> I've defined a guile C function:
>
> static SCM myfun(SCM arg1,SCM opt_arg2)
> {
> return SCM_BOOL_T;
> }
>
> registered with
>
> scm_c_define_gsubr ("myfun", 1, 1, 0, myfun);
>
> there is one optional argument. How can I detect if opt_arg2 has been
> used ?
>
> in
>
> (myfun 1)
>
> or
>
> (myfun 1 2)
>
>
> Thanks !
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next prev parent reply other threads:[~2017-12-14 10:19 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-13 21:50 function registered with scm_c_define_gsubr: how can i handle an optional parameter? Pierre LINDENBAUM
2017-12-14 10:19 ` Alex Vong [this message]
2017-12-14 12:30 ` Mark H Weaver
2017-12-14 13:50 ` Alex Vong
2017-12-15 8:06 ` Mark H Weaver
2017-12-15 16:59 ` Alex Vong
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