GNU bug report logs - #31154
predicate function for foreign-object not obvious

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Package: guile; Reported by: Matt Wette <matt.wette@HIDDEN>; dated Sat, 14 Apr 2018 18:35:01 UTC; Maintainer for guile is bug-guile@HIDDEN.

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Subject: Re: bug#31154: Acknowledgement (predicate function for foreign-object
 not obvious)
To: 31154 <at> debbugs.gnu.org
References: <689d625b-94f7-919b-c017-fa921d54c744@HIDDEN>
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From: Matt Wette <matt.wette@HIDDEN>
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Date: Sat, 14 Apr 2018 12:25:34 -0700
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Perhaps it belongs with the demo in Section 5.5 Defining New Foreign Object Types,
with the image demo.





Information forwarded to bug-guile@HIDDEN:
bug#31154; Package guile. Full text available.

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To: bug-guile@HIDDEN
From: Matt Wette <matt.wette@HIDDEN>
Subject: predicate function for foreign-object not obvious
Message-ID: <689d625b-94f7-919b-c017-fa921d54c744@HIDDEN>
Date: Sat, 14 Apr 2018 11:33:59 -0700
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The reference manual (guile-2.2.3) does not provide instruction on how to generate
a predicate for a foreign object, and it is not obvious.  Maybe it doesn't need to
be in the manual but should then be in an example somewhere, IMO.

The following patch to the reference manual is one option:


--- doc/ref/api-foreign-objects.texi-orig	2018-04-14 11:26:35.779502997 -0700
+++ doc/ref/api-foreign-objects.texi	2018-04-14 11:28:42.823072217 -0700
@@ -96,6 +96,33 @@
  needed.
  @end deftypefn
  
+To generate a predicate for a foreign object use the @code{SCM_IS_A_P}
+macro as follows.
+
+@example
+static SCM foo_type;
+
+static SCM
+scm_foo_p(SCM obj) {
+  return SCM_IS_A_P(obj, foo_type)? SCM_BOOL_T: SCM_BOOL_F;
+}
+
+void
+init_foo()
+{
+  SCM name, slots;
+
+  name = scm_from_utf8_symbol("foo");
+  slots = scm_list_2 (scm_from_utf8_symbol ("data"),
+		      scm_from_utf8_symbol ("deps"));
+  finalizer = NULL;
+  foo_type = scm_make_foreign_object_type(name, slots, finalizer);
+
+  scm_c_define_gsubr("foo?", 1, 0, 0, scm_foo_p);
+  ...
+}
+@end example
+
  One can also access foreign objects from Scheme.  @xref{Foreign Objects
  and Scheme}, for some examples.
  





Acknowledgement sent to Matt Wette <matt.wette@HIDDEN>:
New bug report received and forwarded. Copy sent to bug-guile@HIDDEN. Full text available.
Report forwarded to bug-guile@HIDDEN:
bug#31154; Package guile. Full text available.
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