* Allow to activate strict compile time type checking by defining

the macro SCM_STRICT_TYPING.
* Defined SCM_EQ_P as a macro equivalent for eq?.

libguile/ChangeLog

@@ -1,3 +1,12 @@
+2000-03-25  Dirk Herrmann  <D.Herrmann@tu-bs.de>
+
+	* tags.h (SCM_STRICT_TYPING):  New macro that, if defined,
+	activates strict compile time type checking for variables of
+	type SCM.
+	(SCM, SCM_PACK, SCM_UNPACK):  Define according to whether
+	SCM_STRICT_TYPING or SCM_VOIDP_TEST are defined.
+	(SCM_EQ_P):  Defined as a macro equivalent for eq?.
+
 2000-03-25  Dirk Herrmann  <D.Herrmann@tu-bs.de>
 
 	* tags.h (SCM_POINTERS_MUNGED):  Removed.

libguile/tags.h

@@ -54,25 +54,50 @@
 
 
 
+/* #define SCM_STRICT_TYPING */
+/* #define SCM_VOIDP_TEST    */
 
 /* In the beginning was the Word:
  */
 typedef long scm_bits_t;
-/*
+
-  But as external interface, we use void*, which will be checked more strictly for
+/* But as external interface, we use SCM, which may, according to the desired
-  dubious conversions.
+ * level of type checking, be defined in several ways:
  */
-/* #define SCM_VOIDP_TEST */
+#if defined (SCM_STRICT_TYPING)
-#ifndef SCM_VOIDP_TEST
+/* Use this for _compile time_ type checking only, since the compiled result
-typedef scm_bits_t  SCM;
+ * will be quite inefficient.  The right way to make use of this mode is to do
-#define SCM_UNPACK(x) (x)
+ * a 'make clean' of your project, 'make all CFLAGS=-DSCM_STRICT_TYPING', fix
-#define SCM_PACK(x) (x)
+ * your errors, and then do 'make clean; make all'.
+*/
+    typedef union { struct { scm_bits_t n; } n; } SCM;
+    static SCM scm_pack(scm_bits_t b) { SCM s; s.n.n = b; return s; }
+    #define SCM_UNPACK(x) ((x).n.n)
+    #define SCM_PACK(x) (scm_pack (x))
+#elif defined (SCM_VOIDP_TEST)
+/* This is the default, which provides an intermediate level of compile time
+ * type checking while still resulting in very efficient code.
+ */
+    typedef void * SCM;
+    #define SCM_UNPACK(x) ((scm_bits_t) (x))
+    #define SCM_PACK(x) ((SCM) (x))
 #else
-typedef void * SCM;
+/* This should be used as a fall back solution for machines on which casting
-#define SCM_UNPACK(x) ((scm_bits_t) (x))
+ * to a pointer may lead to loss of bit information, e. g. in the three least
-#define SCM_PACK(x) ((SCM) (x))
+ * significant bits.
+ */
+    typedef scm_bits_t SCM;
+    #define SCM_UNPACK(x) (x)
+    #define SCM_PACK(x) (x)
 #endif
 
+
+/* SCM values can not be compared by using the operator ==.  Use the following
+ * macro instead, which is the equivalent of the scheme predicate 'eq?'.
+ */
+#define SCM_EQ_P(x, y) (SCM_UNPACK (x) == SCM_UNPACK (y))
+
+
 /* SCM_UNPACK_CAR is a convenience for treating the CAR of X as a word */
 #define SCM_UNPACK_CAR(x) SCM_UNPACK (SCM_CAR (x))
 
@@ -81,8 +106,8 @@ typedef void * SCM;
  * rather than each byte, the 3 most significant bits encode the byte
  * within the word.  The following macros deal with this by storing the
  * native Cray pointers like the ones that looks like scm expects.  This
- * is done for any pointers that might appear in the car of a scm_cell, pointers
+ * is done for any pointers that might appear in the car of a scm_cell,
- * to scm_vector elts, functions, &c are not munged.
+ * pointers to scm_vector elts, functions, &c are not munged.
  */
 #ifdef _UNICOS
 # define SCM2PTR(x) ((void *) (SCM_UNPACK (x) >> 3))