X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcompiler%2Fgeneric%2Fobjdef.lisp;h=bf9217d7750cb3cd68a82c3ac936c85a6a7b8648;hb=5edd74f6911093805a009a152b32216b3dba59f7;hp=786c9d4c5f5df13a118cd32e0b712ba67b15a6c7;hpb=90ca09b75fbc3b63b2f7d09c67b04b866dd783f6;p=sbcl.git

diff --git a/src/compiler/generic/objdef.lisp b/src/compiler/generic/objdef.lisp
index 786c9d4..bf9217d 100644
--- a/src/compiler/generic/objdef.lisp
+++ b/src/compiler/generic/objdef.lisp
@@ -193,7 +193,8 @@
 	:ref-trans %simple-fun-name
 	:set-known (unsafe)
 	:set-trans (setf %simple-fun-name))
-  (arglist :ref-known (flushable)
+  (arglist :type list
+           :ref-known (flushable)
 	   :ref-trans %simple-fun-arglist
 	   :set-known (unsafe)
 	   :set-trans (setf %simple-fun-arglist))
@@ -315,9 +316,20 @@
 (define-primitive-object (symbol :lowtag other-pointer-lowtag
 				 :widetag symbol-header-widetag
 				 #!-x86 :alloc-trans #!-x86 make-symbol)
+
+  ;; Beware when changing this definition.  NIL-the-symbol is defined
+  ;; using this layout, and NIL-the-end-of-list-marker is the cons 
+  ;; ( NIL . NIL ), living in the first two slots of NIL-the-symbol
+  ;; (conses have no header).  Careful selection of lowtags ensures
+  ;; that the same pointer can be used for both purposes:
+  ;; OTHER-POINTER-LOWTAG is 7, LIST-POINTER-LOWTAG is 3, so if you
+  ;; subtract 3 from (sb-kernel:get-lisp-obj-address 'NIL) you get the
+  ;; first data slot, and if you subtract 7 you get a symbol header.
+
   (value :set-trans %set-symbol-value
-	 :init :unbound)
-  #!+x86 (hash)
+	 :init :unbound)		;also the CAR of NIL-as-end-of-list
+  (hash)				;the CDR of NIL-as-end-of-list
+
   (plist :ref-trans symbol-plist
 	 :set-trans %set-symbol-plist
 	 :init :null)