Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!ai.etl.army.mil!hoey
From: hoey@ai.etl.army.mil (Dan Hoey)
Newsgroups: comp.lang.lisp
Subject: Re: multiple values and conditionals
Message-ID: <293@ai.etl.army.mil>
Date: 25 Apr 89 18:30:43 GMT
References: <886@cadillac.CAD.MCC.COM>
Reply-To: hoey@ai.etl.army.mil (Dan Hoey)
Organization: USAETL, Fort Belvoir, Virginia
Lines: 16

In article <886@cadillac.CAD.MCC.COM> vaughan@puma.cad.mcc.com (Paul Vaughan)
writes of a multiple-value OR, specified to return all the values of the
first form that returns a non-NIL first value.  He motivates it with

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

But in this case we probably want a MV-OR that returns the values of the
first form to return a non-NIL *second* value.  Furthermore, using a
generalized MV-OR requires MULTIPLE-VALUE-LIST, which conses; for combining
results of GETHASH we prefer MULTIPLE-VALUE-BIND or MULTIPLE-VALUE-SETQ, which
generate no garbage but must be written with knowledge of the number of values
to handle.

Dan