Sat Apr  2 04:01:24 UTC 2011  mantoniotti@common-lisp.net
  * Changed some environment functions and improved the DUMP-* ones.
diff -rN -u old-cl-unification/substitutions.lisp new-cl-unification/substitutions.lisp
--- old-cl-unification/substitutions.lisp	2013-11-10 20:09:45.000000000 +0000
+++ new-cl-unification/substitutions.lisp	2013-11-10 20:09:46.000000000 +0000
@@ -113,10 +113,23 @@
   (make-environment :frames (list (make-frame))))
 
 (defun copy-environment (env)
+  (declare (type environment env))
   (make-environment :frames (copy-list (environment-frames env))))
 
-(defun make-shared-environment (env)
-  (make-environment :frames (environment-frames env)))
+(defun make-shared-environment (env &optional (pushp nil))
+  (declare (type environment env))
+  (make-environment :frames (if pushp
+                                (cons (make-frame) (environment-frames env))
+                                (environment-frames env))))
+
+(defun push-frame (env)
+  (declare (type environment env))
+  (push (make-frame) (environment-frames env)))
+
+(defun pop-frame (env)
+  (declare (type environment env))
+  (pop (environment-frames env)))
+
 
 (defun make-expanded-environment (base-env)
   (make-environment :frames (cons (make-frame) (environment-frames base-env))))
@@ -192,13 +205,20 @@
 
 (defun dump-frame (f &optional (out *standard-output*))
   (declare (type frame f))
-  (terpri out)
   (loop for (var . value) in (frame-bindings f)
-        do (format out "~A~VT= ~A~%" var 8 value))
+        do (format out "~&~A~VT= ~A~%" var 8 value))
   )
 
 (defun dump-environment (env &optional (out *standard-output*))
   (declare (type environment env))
-  (map nil #'(lambda (f) (dump-frame f out)) (environment-frames env)))
+  (if (empty-environment-p env)
+      (format out ">>> Empty unify environment ~S.~%" env)
+      (loop initially (format out ">>> Dumping unify environment ~S.~%" env)
+            for fr in (environment-frames env)
+            for fr-n downfrom (list-length (environment-frames env))
+            do (format out ">>> Frame ~D:~%" fr-n)
+            do (dump-frame fr out)
+            do (terpri out)
+            )))
 
 ;;;; end of file -- substitutions.lisp --