Re: Argument lists: a proposal to shoot at

[David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>]

    Date: Fri, 27 Jun 86 14:45 EDT
    From: Guy Steele <gls@Think.COM>

	Date: 26 Jun 1986 19:17-EDT
	From: NGALL@G.BBN.COM

	How about keeping the number of functions down and eliminating the
	'encoding' in MAX-ARGS, and using correct terminology with the
	following one-function alternative to FUNCTION-MIN-ARGS, -MAX-ARGS,
	-HAS-KEYWORD-PARAMETERS, and -KEYWORD-PARAMETERS.  I think
	FUNCTION-KEYWORD-PARAMETER-P addresses an idiom common enough to
	warrant its own function.

	FUNCTION-PARAMETERS function				[Function]

	Returns Q, P, R, K, a list of keywords explicitly accepted by the
	function (order undefined), and A.  Note that if K is false, the list
	is necessarily empty.

I like one function to return all the information better than a bunch of
separate functions.  As for whether it's better to return min-and-max or
required-and-optional, in all these years I've never made up my mind on
that point.  I do think it's a good idea for the presence of &rest or &key
not to throw away the information about how many positional parameters
there are, even if some of the proposed uses for that information are
bad ideas.  In the min-and-max model, max could be the maximum number
of positional parameters, thus you have to look at (OR R K) to know
whether this is actually the maximum you are permitted to pass.

    I have to admit (blush) that another design criterion I employed implicitly
    was that it should be possible to acquire most of the information without
    either consing on the fly or requiring an explicit pre-stored list of the
    keywords.

I don't understand how the information would be accessible at all if
there was not a pre-stored list.  Perhaps you have some clever
implementation in mind?  If this is really important, we could have both
FUNCTION-PARAMETERS and FUNCTION-KEYWORD-PARAMETER-P, with some way to
tell FUNCTION-PARAMETERS not to bother creating the list.  But I like it
better with just one function.  Anyway I know how to not be bothered
by consing on the fly.

    In your proposal for FUNCTION-PARAMETERS, I observe that returning K
    is redundant: K is true iff [(the keyword list is not empty) or A].
    That's not to say that returning K separately isn't a good idea.
    
(defun foo (&key) ...) has some semantic meaning, namely that if this
function is ever extended it's going to take keyword parameters.  If you
don't think this is a realistic example, see CLtL page 427.
I don't think clever elimination of the K return value is advisable.