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5 points by kennytilton 5869 days ago | link | parent

Isn't destructuring cool? We take an anonymous list and quickly associate useful names with what otherwise would be car, cadr, and caddr, etc.

In common lisp when we use destructuring-bind we can have optional /and/ keyword arguments, so you can plan ahead and create an adhoc list like (1 2 :height 3 :width 4) and let :weight default to 42:

  (destructuring-bind (x y &key (height )(width 0)(weight 42))
      ..etc with x, y, height, width, and weight...)
Hmmm, I think I did that for my Arc implementation of defun...shuffle, shuffle, dig..ah:

   (mac defun (name params . body)
  (w/uniq (rtargs)
    `(def ,name ,rtargs
       (withs ,(with (reqs nil key? nil opt? nil keys nil opts nil without)
                (each p params
                  (if (is p '&o) (do (assert (no opt?) "Duplicate &o:" ',params)
                                     (assert (no key?) "&k cannot precede &o:" ',params)
                                   (= opt? t))
                    (is p '&k) (do (assert (no key?) "Duplicate &k:" ',params)
                                   (= key? t))
                    key? (push-end p keys)
                    opt? (push-end p opts)
                    (do (assert (~acons p) "Reqd parameters need not be defaulted:" p)
                        (push-end p reqs))))
                (with (n -1 kvs (uniq))
                  (+ (mappend [list _ `(nth ,(++ n) ,rtargs)] reqs)
                    (mappend [list (carif _) `(or (nth ,(++ n) ,rtargs)
                                                ,(cadrif _))] opts)
                    (list kvs `(pair (nthcdr ,(++ n) ,rtargs)))
                    (mappend [list (carif _)
                               `(or (alref ,kvs ',(carif _))
                                       ,(cadrif _))] keys)
                    )))
         ,@body))))
I'll carve out a dsb tomorrow.