* lily/identifier-smob.cc (unpack_identifier): new file.

[lilypond.git] / lily / identifier-smob.cc

diff --git a/lily/identifier-smob.cc b/lily/identifier-smob.cc
new file mode 100644 (file)
index 0000000..2d38045
--- /dev/null
+++ b/lily/identifier-smob.cc
@@ -0,0 +1,61 @@
+/*   
+identifier-smob.cc -- implement glue to pass Scheme expressions off as
+identifiers.
+
+source file of the GNU LilyPond music typesetter
+
+(c) 2002 Han-Wen Nienhuys <hanwen@cs.uu.nl>
+
+*/
+#include "identifier-smob.hh"
+/*
+  C&P from example/box.c
+ */
+
+scm_t_bits package_tag;
+
+/* Print a textual represenation of the smob to a given port.  */
+static int
+print_box (SCM b, SCM port, scm_print_state *pstate)
+{
+  SCM value = SCM_CELL_OBJECT_1 (b);
+
+  scm_puts ("#<packaged object ", port);
+  scm_write (value, port);
+  scm_puts (">", port);
+
+  /* Non-zero means success.  */
+  return 1;
+}
+
+
+/* This defines the primitve `make-box', which returns a new smob of
+   type `box', initialized to `#f'.  */
+LY_DEFINE(package_identifier, "ly-id", 1,0,0, (SCM arg),
+         "Package a Scheme object, so it is treated as an identifier.")
+{
+  /* This macro creates the new objects, stores the value `#f' into it
+     and returns it to the caller.  */
+  SCM_RETURN_NEWSMOB (package_tag, arg);
+}
+
+
+/* This is the primitive `box-ref' which returns the object stored in
+   the box.  */
+SCM
+unpack_identifier(SCM box)
+{
+  if (SCM_IMP(box) || SCM_CELL_TYPE(box) != package_tag)
+    return SCM_UNDEFINED;
+  
+  return SCM_CELL_OBJECT_1 (box);
+}
+
+static void
+init_box_type (void)
+{
+  package_tag = scm_make_smob_type ("box", 0);
+  scm_set_smob_mark (package_tag, scm_markcdr);
+  scm_set_smob_print (package_tag, print_box);
+}
+ADD_SCM_INIT_FUNC(package, init_box_type);