Path: utzoo!utgpu!attcan!uunet!cs.utexas.edu!pp!cadillac!puma!vaughan
From: vaughan@puma.cad.mcc.com (Paul Vaughan)
Newsgroups: comp.lang.lisp
Subject: multiple values and conditionals
Message-ID: <886@cadillac.CAD.MCC.COM>
Date: 21 Apr 89 19:31:07 GMT
Sender: news@cadillac.CAD.MCC.COM
Lines: 25

This is a specification for a multiple-value handling OR construct.  It
behaves like the traditional OR, but returns all the values of the first
form which returns a non-nil first value.  (The usual OR does this only
if the first such form is the last form, otherwise, it returns only the
first value.)

(defmacro mv-or (&rest forms)
  (cond ((null forms) nil)
	((null (cdr forms)) (first forms))
	(t (let ((values-symbol (gensym "VALUES")))
	     `(let ((,values-symbol (multiple-value-list ,(first forms))))
		(if (car ,values-symbol) (values-list ,values-symbol)
		    (mv-or . ,(cdr forms))))))))

I might use it in a function that did something like

(defun lookup (key primary-table secondary-table)
  (declare (values value found found-key))
  (mv-or (gethash key primary-table) (gethash key secondary-table)))

Somebody please tell me why such a thing is stupid, unnecessary, or
should never arise.

 Paul Vaughan, MCC CAD Program | ARPA: vaughan@mcc.com | Phone: [512] 338-3639
 Box 200195, Austin, TX 78720  | UUCP: ...!cs.utexas.edu!milano!cadillac!vaughan