collect: Reduce consing.

[lisp] / mdw-base.lisp

diff --git a/mdw-base.lisp b/mdw-base.lisp
index cde1d7a..6b235f5 100644 (file)
--- a/mdw-base.lisp
+++ b/mdw-base.lisp
@@ -179,21 +179,26 @@
        (,kind ,scrutinee
         ,@(mapcar (lambda (clause)
                     (destructuring-bind
-                        (cases (&optional var) &rest forms)
+                        (cases (&optional varx vary) &rest forms)
                         clause
                       `(,cases
-                        ,@(if var
-                              (list `(let ((,var ,argument)) ,@forms))
+                        ,@(if varx
+                              (list `(let ((,(or vary varx) ,argument)
+                                           ,@(and vary
+                                                  `((,varx ,scrutinee))))
+                                       ,@forms))
                               forms))))
                   clauses)))))
 
 (defmacro case2 (vform &body clauses)
   "VFORM is a form which evaluates to two values, SCRUTINEE and ARGUMENT.
-   The CLAUSES have the form (CASES ([VAR]) FORMS...), where a standard
-   `case' clause has the form (CASES FORMS...).  The `case2' form evaluates
-   the VFORM, and compares the SCRUTINEE to the various CASES, in order, just
-   like `case'.  If there is a match, then the corresponding FORMs are
-   evaluated with VAR (if specified) bound to the value of ARGUMENT."
+   The CLAUSES have the form (CASES ([[SCRUVAR] ARGVAR]) FORMS...), where a
+   standard `case' clause has the form (CASES FORMS...).  The `case2' form
+   evaluates the VFORM, and compares the SCRUTINEE to the various CASES, in
+   order, just like `case'.  If there is a match, then the corresponding
+   FORMs are evaluated with ARGVAR bound to the ARGUMENT and SCRUVAR bound to
+   the SCRUTINEE (where specified).  Note the bizarre defaulting behaviour:
+   ARGVAR is less optional than SCRUVAR."
   (do-case2-like 'case vform clauses))
 
 (defmacro ecase2 (vform &body clauses)