Add 'supports-source-properties?' predicate

* libguile/srcprop.c (scm_supports_source_properties_p): New procedure.
  (supports_source_props): New static C function.

* libguile/srcprop.h (scm_supports_source_properties_p): Add prototype.

* doc/ref/api-debug.texi (Source Properties): Add documentation.

3 files changed, 27 insertions, 1 deletions

diff --git a/doc/ref/api-debug.texi b/doc/ref/api-debug.texi
index c5fbe5629..18371f0fc 100644
--- a/doc/ref/api-debug.texi
+++ b/doc/ref/api-debug.texi
@@ -258,6 +258,12 @@ ERROR: Unbound variable: xxx
 In the latter case, no source properties were stored, so the error
 doesn't have any source information.
 
+@deffn {Scheme Procedure} supports-source-properties? obj
+@deffnx {C Function} scm_supports_source_properties_p (obj)
+Return #t if source properties can be associated with @var{obj},
+otherwise return #f.
+@end deffn
+
 The recording of source properties is controlled by the read option
 named ``positions'' (@pxref{Scheme Read}).  This option is switched
 @emph{on} by default.
diff --git a/libguile/srcprop.c b/libguile/srcprop.c
index c43acdf95..c632bb0c5 100644
--- a/libguile/srcprop.c
+++ b/libguile/srcprop.c
@@ -94,6 +94,14 @@ static SCM scm_srcprops_to_alist (SCM obj);
 
 scm_t_bits scm_tc16_srcprops;
 
+
+static int
+supports_source_props (SCM obj)
+{
+  return SCM_NIMP (obj) && !scm_is_symbol (obj) && !scm_is_keyword (obj);
+}
+
+
 static int
 srcprops_print (SCM obj, SCM port, scm_print_state *pstate)
 {
@@ -160,6 +168,16 @@ scm_srcprops_to_alist (SCM obj)
   return alist;
 }
 
+SCM_DEFINE (scm_supports_source_properties_p, "supports-source-properties?", 1, 0, 0,
+            (SCM obj),
+            "Return #t if @var{obj} supports adding source properties,\n"
+            "otherwise return #f.")
+#define FUNC_NAME s_scm_supports_source_properties_p
+{
+  return scm_from_bool (supports_source_props (obj));
+}
+#undef FUNC_NAME
+
 SCM_DEFINE (scm_source_properties, "source-properties", 1, 0, 0, 
             (SCM obj),
 	    "Return the source property association list of @var{obj}.")
diff --git a/libguile/srcprop.h b/libguile/srcprop.h
index 250756dcc..0252e54a1 100644
--- a/libguile/srcprop.h
+++ b/libguile/srcprop.h
@@ -3,7 +3,8 @@
 #ifndef SCM_SRCPROP_H
 #define SCM_SRCPROP_H
 
-/* Copyright (C) 1995,1996,2000,2001, 2006, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
+/* Copyright (C) 1995, 1996, 2000, 2001, 2006, 2008, 2009, 2010,
+ *   2011, 2012 Free Software Foundation, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -41,6 +42,7 @@ SCM_API SCM scm_sym_column;
 
 
 
+SCM_API SCM scm_supports_source_properties_p (SCM obj);
 SCM_API SCM scm_make_srcprops (long line, int col, SCM fname, SCM copy, SCM plist);
 SCM_API SCM scm_source_property (SCM obj, SCM key);
 SCM_API SCM scm_set_source_property_x (SCM obj, SCM key, SCM datum);