The GOOPS "unbound" value is a unique pair

* libguile/goops.c (SCM_GOOPS_UNBOUND, SCM_GOOPS_UNBOUNDP): Remove
  internal macros.
  (scm_make_unbound, scm_unbound_p): Remove internal functions.
  (scm_sys_clear_fields_x): Add "unbound" parameter, for the init
  value.

* module/oop/goops.scm (*unbound*): Define in Scheme as a simple
  heap-allocated value.
  (unbound?): New definition.
  (%allocate-instance): Pass *unbound* to %clear-fields!.
  (make-class, slot-definition-init-value)
  (slot-definition-init-form, make-closure-variable): Use *unbound*
  instead of (make-unbound), which is now gone.

* module/oop/goops/active-slot.scm (compute-get-n-set): Use *unbound*
  instead of make-unbound.  This module uses the GOOPS internals module;
  perhaps we should export make-unbound or something...

* module/oop/goops/save.scm (make-unbound): Export our own make-unbound
  definition, for use by residualized save code.

* module/language/ecmascript/base.scm (<undefined>, *undefined*): Use a
  unique object kind and instance for the undefined value.

* libguile/vm.c (scm_i_vm_mark_stack): Fill the stack with
  SCM_UNSPECIFIED instead of SCM_UNBOUND.

libguile/goops.c

@@ -55,9 +55,6 @@
 #define SCM_OUT_PCLASS_INDEX      SCM_I_MAX_PORT_TYPE_COUNT
 #define SCM_INOUT_PCLASS_INDEX    (2 * SCM_I_MAX_PORT_TYPE_COUNT)
 
-#define SCM_GOOPS_UNBOUND SCM_UNBOUND
-#define SCM_GOOPS_UNBOUNDP(x) (scm_is_eq (x, SCM_GOOPS_UNBOUND))
-
 /* Objects have identity, so references to classes and instances are by
    value, not by reference.  Redefinition of a class or modification of
    an instance causes in-place update; you can think of GOOPS as
@@ -149,11 +146,9 @@ SCM scm_i_smob_class[SCM_I_MAX_SMOB_TYPE_COUNT];
 
 SCM scm_module_goops;
 
-static SCM scm_make_unbound (void);
-static SCM scm_unbound_p (SCM obj);
 static SCM scm_sys_make_vtable_vtable (SCM layout);
 static SCM scm_sys_init_layout_x (SCM class, SCM layout);
-static SCM scm_sys_clear_fields_x (SCM obj);
+static SCM scm_sys_clear_fields_x (SCM obj, SCM unbound);
 static SCM scm_sys_goops_early_init (void);
 static SCM scm_sys_goops_loaded (void);
 
@@ -426,27 +421,6 @@ scm_method_procedure (SCM obj)
 }
 
 
-
-
-SCM_DEFINE (scm_make_unbound, "make-unbound", 0, 0, 0,
-	    (),
-	    "Return the unbound value.")
-#define FUNC_NAME s_scm_make_unbound
-{
-  return SCM_GOOPS_UNBOUND;
-}
-#undef FUNC_NAME
-
-SCM_DEFINE (scm_unbound_p, "unbound?", 1, 0, 0,
-	    (SCM obj),
-	    "Return @code{#t} if @var{obj} is unbound.")
-#define FUNC_NAME s_scm_unbound_p
-{
-  return SCM_GOOPS_UNBOUNDP (obj) ? SCM_BOOL_T : SCM_BOOL_F;
-}
-#undef FUNC_NAME
-
-
 
 
 SCM
@@ -476,8 +450,8 @@ scm_slot_exists_p (SCM obj, SCM slot_name)
 
 
 
-SCM_DEFINE (scm_sys_clear_fields_x, "%clear-fields!", 1, 0, 0,
-	    (SCM obj),
+SCM_DEFINE (scm_sys_clear_fields_x, "%clear-fields!", 2, 0, 0,
+	    (SCM obj, SCM unbound),
             "")
 #define FUNC_NAME s_scm_sys_clear_fields_x
 {
@@ -493,7 +467,7 @@ SCM_DEFINE (scm_sys_clear_fields_x, "%clear-fields!", 1, 0, 0,
   /* Set all SCM-holding slots to the GOOPS unbound value.  */
   for (i = 0; i < n; i++)
     if (scm_i_symbol_ref (layout, i*2) == 'p')
-      SCM_STRUCT_SLOT_SET (obj, i, SCM_GOOPS_UNBOUND);
+      SCM_STRUCT_SLOT_SET (obj, i, unbound);
 
   return SCM_UNSPECIFIED;
 }

libguile/vm.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 2001, 2009, 2010, 2011, 2012, 2013, 2014 Free Software Foundation, Inc.
+/* Copyright (C) 2001, 2009, 2010, 2011, 2012, 2013, 2014, 2015 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
@@ -990,7 +990,7 @@ scm_i_vm_mark_stack (struct scm_vm *vp, struct GC_ms_entry *mark_stack_ptr,
                     {
                       /* This value may become dead as a result of GC,
                          so we can't just leave it on the stack.  */
-                      *sp = SCM_UNBOUND;
+                      *sp = SCM_UNSPECIFIED;
                       continue;
                     }
                 }

module/language/ecmascript/base.scm

@@ -1,6 +1,6 @@
 ;;; ECMAScript for Guile
 
-;; Copyright (C) 2009, 2013 Free Software Foundation, Inc.
+;; Copyright (C) 2009, 2013, 2015 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
@@ -35,7 +35,9 @@
 
             new-object new))
 
-(define *undefined* ((@@ (oop goops) make-unbound)))
+(define-class <undefined> ())
+
+(define *undefined* (make <undefined>))
 (define *this* (make-fluid))
 
 (define-class <js-object> ()

module/oop/goops.scm

@@ -769,9 +769,14 @@ followed by its associated value.  If @var{l} does not hold a value for
          (scm-error 'wrong-type-arg #f "Not a keyword: ~S" (list kw) #f))
        (if (eq? kw key) arg (lp l))))))
 
+(define *unbound* (list 'unbound))
+
+(define-inlinable (unbound? x)
+  (eq? x *unbound*))
+
 (define (%allocate-instance class)
   (let ((obj (allocate-struct class (struct-ref class class-index-nfields))))
-    (%clear-fields! obj)
+    (%clear-fields! obj *unbound*)
     obj))
 
 (define (make class . args)
@@ -1302,7 +1307,7 @@ followed by its associated value.  If @var{l} does not hold a value for
            head
            (find-duplicate tail)))))
 
-  (let* ((name (get-keyword #:name options (make-unbound)))
+  (let* ((name (get-keyword #:name options *unbound*))
          (supers (if (not (or-map (lambda (class)
                                     (memq <object>
                                           (class-precedence-list class)))
@@ -1947,10 +1952,10 @@ followed by its associated value.  If @var{l} does not hold a value for
 
 (define (slot-definition-init-value s)
   ;; can be #f, so we can't use #f as non-value
-  (get-keyword #:init-value (cdr s) (make-unbound)))
+  (get-keyword #:init-value (cdr s) *unbound*))
 
 (define (slot-definition-init-form s)
-  (get-keyword #:init-form (cdr s) (make-unbound)))
+  (get-keyword #:init-form (cdr s) *unbound*))
 
 (define (slot-definition-init-thunk s)
   (get-keyword #:init-thunk (cdr s) #f))
@@ -2561,8 +2566,6 @@ followed by its associated value.  If @var{l} does not hold a value for
 ;;; {Initialize}
 ;;;
 
-(define *unbound* (make-unbound))
-
 ;; FIXME: This could be much more efficient.
 (define (%initialize-object obj initargs)
   "Initialize the object @var{obj} with the given arguments

module/oop/goops/active-slot.scm

@@ -38,7 +38,7 @@
 	     (after-ref   (get-keyword #:after-slot-ref   s #f))
 	     (before-set! (get-keyword #:before-slot-set! s #f))
 	     (after-set!  (get-keyword #:after-slot-set!  s #f))
-	     (unbound	  (make-unbound)))
+	     (unbound	  *unbound*))
 	(slot-set! class 'nfields (+ index 1))
 	(list (lambda (o)
 		(if before-ref
@@ -46,7 +46,7 @@
 			(let ((res (struct-ref o index)))
 			  (and after-ref (not (eqv? res unbound)) (after-ref o))
 			  res)
-			(make-unbound))
+			*unbound*)
 		    (let ((res (struct-ref o index)))
 		      (and after-ref (not (eqv? res unbound)) (after-ref o))
 		      res)))

module/oop/goops/save.scm

@@ -20,12 +20,14 @@
 
 (define-module (oop goops save)
   :use-module (oop goops internal)
-  :re-export (make-unbound)
-  :export (save-objects load-objects restore
+  :export (make-unbound save-objects load-objects restore
 	   enumerate! enumerate-component!
 	   write-readably write-component write-component-procedure
 	   literal? readable make-readable))
 
+(define (make-unbound)
+  *unbound*)
+
 ;;;
 ;;; save-objects ALIST PORT [EXCLUDED] [USES]
 ;;;