Fri Jan 15 08:49:26 UTC 2010  pix@kepibu.org
  * Only use one variable to store the unification environment in MATCHING
  Because of the way MATCHING expands, and what UNIFY* returns, each
    (setf #:env (unify* ...))
  call will do one of two things: it will set #:env to NIL or it will set #:env to
  an ENVIRONMENT structure.
  
  If #:env is set to NIL--the same value it entered the (setf) with!--the COND
  will continue on to the next clause.
  
  If #:env is set to an ENVIRONMENT structure, none of the remaining (setf)
  clauses will be evaluated.
  
  Thus, because the variable will only ever be set to a non-nil value once, this
  should be perfectly safe.
diff -rN -u old-cl-unification-2/match-block.lisp new-cl-unification-2/match-block.lisp
--- old-cl-unification-2/match-block.lisp	2014-09-11 07:36:01.000000000 +0000
+++ new-cl-unification-2/match-block.lisp	2014-09-11 07:36:02.000000000 +0000
@@ -192,21 +192,16 @@
            (match-clauses (delete default-clause match-clauses)) ; EQL
                                                                  ; test
                                                                  ; suffices.
-           (match-clauses-env-vars (mapcar (lambda (mc)
-                                             (declare (ignore mc))
-                                             (gensym "UNIFICATION-ENV-")
-                                             )
-                                           match-clauses))
+           (env-var (gensym "UNIFICATION-ENV-"))
            )
 
       `(block ,matching-named
-         (let ,match-clauses-env-vars
-	   (declare (dynamic-extent ,@match-clauses-env-vars))
-           (cond ,@(mapcar (lambda (match-clause match-clause-env-var)
+         (let (,env-var)
+           (declare (dynamic-extent ,env-var))
+           (cond ,@(mapcar (lambda (match-clause)
                              (build-match-clause match-clause
-                                                 match-clause-env-var))
-                           match-clauses
-                           match-clauses-env-vars)
+                                                 env-var))
+                           match-clauses)
                  (,errorp
                   (error 'unification-non-exhaustive
                          :format-control "Non exhaustive matching."))