From: Daniel Gackle <danielgackle@gmail.com>
Date: Fri, 8 May 2009 20:59:05 +0000 (-0600)
Subject: Extended DESTRUCTURING-BIND to allow NIL bindings to indicate a place should be ignor... 
X-Git-Url: http://git.hcoop.net/clinton/parenscript.git/commitdiff_plain/6e135d5caec3096c8ce072c8f34a1610e7007bf0

Extended DESTRUCTURING-BIND to allow NIL bindings to indicate a place should be ignored, the way that CL LOOP does.
---

diff --git a/src/lib/ps-macro-lib.lisp b/src/lib/ps-macro-lib.lisp
index e3341e0..cb413cf 100644
--- a/src/lib/ps-macro-lib.lisp
+++ b/src/lib/ps-macro-lib.lisp
@@ -137,10 +137,13 @@
     `((@ ,fn :apply) this ,arglist)))
 
 (defpsmacro destructuring-bind (vars expr &body body)
-  ;; a simple implementation that for now only supports flat lists
+  ;; a simple implementation that for now only supports flat lists,
+  ;; but does allow NIL bindings to indicate ignore (a la LOOP)
   (let* ((arr (if (complex-js-expr? expr) (ps-gensym) expr))
          (n -1)
          (bindings
           (append (unless (equal arr expr) `((,arr ,expr)))
-                  (mapcar (lambda (var) `(,var (aref ,arr ,(incf n)))) vars))))
+                  (mapcan (lambda (var)
+                            (incf n)
+                            (when var `((,var (aref ,arr ,n))))) vars))))
     `(let ,bindings ,@body)))