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From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.lang.scheme
Subject: Re: Why memq vs memv vs member, etc.?
Message-ID: <5816@goanna.cs.rmit.oz.au>
Date: 18 May 91 09:24:51 GMT
References: <1991May10.230057.15591@Think.COM> <chip.674143084@soi> <chip.674492719@soi>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 36

In article <chip.674492719@soi>, chip@soi.UUCP (Chip Morris) writes:
> >I guess the only problem with optimizing out the explicit passing of
> >the eq argument is that Scheme doesn't prohibit user programs from
> >redefining standard procedure names as Common Lisp does.  
> 
> Perhaps one must grudgingly admit an analysis advantage to Common
> Lisp's otherwise distressingly assymetrical treatment of the function
> position.

Looking at CLtL2, section 5.3.1, all I can see that bears on this is
the final paragraph:
	It is permissible to use DEFUN to redefine a function,
	to install a corrected version of an incorrect definition,
	for example.
	It is permissible to redefine a macro as a function.
	It is an error to attempt to redefine the name of a ***special form***
	(see table 5-1) as a function.
I have not been able to find the alleged prohibition in the indexed pages
describing DEFUN, FLET, or LABELS.  Given that MEMBER is not a special form,
what section of CLtL2 prohibits redefinition?

Also, the analysis advantage, if it does exist, would only apply to
predefined function names.  For user-defined functions, we have
    ;;  Lisp      Scheme
	DEFUN	: SET!			; functions can be redefined
    ::	FLET	: LET			; or locally rebound
    ::	LABELS	: LETREC		; in _both_ languages.
CL _does_ have a way for users to declare things that can't be changed,
but because of CL's "two name-spaces" approach, DEFCONSTANT _can't_ be
used to define non-redefinable functions.  Those Scheme dialects having
define-constant and/or define-integrable _do_ allow users to write
function definitions which can be optimised in the way that we'd like
a generic MEMBER to be optimised.

-- 
There is no such thing as a balanced ecology; ecosystems are chaotic.