From: "Pascal J. Bourguignon" <pjb@informatimago.com>
To: help-gnu-emacs@gnu.org
Subject: Re: why are there [v e c t o r s] in Lisp?
Date: Sat, 17 Oct 2015 03:55:15 +0200 [thread overview]
Message-ID: <87twpqcl8c.fsf@kuiper.lan.informatimago.com> (raw)
In-Reply-To: mailman.482.1445037713.7904.help-gnu-emacs@gnu.org
Emanuel Berg <embe8573@student.uu.se> writes:
> Random832 <random832@fastmail.com> writes:
>
>> The thing is, if you can car a string people will
>> wonder why you can't cdr it. And with mutable
>> objects it's hard to make cdr work right. (fsvo
>> "right")
>
> You can't `car' a string or do anything with it that
> requires it to be a list, because it isn't. If you try
> to car it, the string will fail the `listp' test.
> But because it is natural to think of strings as lists
> of chars, perhaps from the C days of, say
>
> char *str = malloc(strlen(argv[argc - 1]));
>
> or actually because it is normal for humans to think
> of strings that way, it should be pointed out - and
> now that has happened - that the "string" syntax isn't
> a shorthand for creating lists of chars.
In emacs lisp it'd be difficult to do it, but in Common Lisp it's
trivial:
(defpackage "EB-LISP"
(:use "COMMON-LISP")
(:shadow "CAR" "CDR" "CONSP" "LISTP")
(:export . #.(let ((syms '()))
(do-external-symbols (s "COMMON-LISP" syms)
(push (symbol-name s) syms)))))
(in-package "EB-LISP")
(defun car (x)
(if (vectorp x)
(aref x 0)
(cl:car x)))
(defun cdr (x)
(if (vectorp x)
(if (< 1 (length x))
(make-array (1- (length x))
:element-type (array-element-type x)
:displaced-to x
:displaced-index-offset 1)
'())
(cl:cdr x)))
(defun consp (x)
(or (vectorp x) (cl:consp x)))
(defun listp (x)
(or (vectorp x) (cl:listp x)))
(defpackage "EB-LISP-USER"
(:use "EB-LISP"))
(in-package "EB-LISP-USER")
(loop :for string := "hello world" :then (cdr string)
:while string
:collect (car string))
;; --> (#\h #\e #\l #\l #\o #\ #\w #\o #\r #\l #\d)
Instead, in emacs-lisp you can prefix your symbols: eb-lisp-car
eb-lisp-cdr etc… (and you have to implement more things yourself, since
there are no displaced arrays, etc).
--
__Pascal Bourguignon__ http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk
next prev parent reply other threads:[~2015-10-17 1:55 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.428.1444957396.7904.help-gnu-emacs@gnu.org>
2015-10-16 1:51 ` why are there [v e c t o r s] in Lisp? Pascal J. Bourguignon
2015-10-16 2:31 ` Emanuel Berg
2015-10-16 2:29 ` Random832
2015-10-16 2:51 ` Emanuel Berg
2015-10-16 2:56 ` Random832
2015-10-16 23:30 ` Emanuel Berg
[not found] ` <mailman.482.1445037713.7904.help-gnu-emacs@gnu.org>
2015-10-17 1:55 ` Pascal J. Bourguignon [this message]
2015-10-17 4:47 ` Emanuel Berg
[not found] ` <mailman.494.1445057637.7904.help-gnu-emacs@gnu.org>
2015-10-17 15:25 ` Pascal J. Bourguignon
2015-10-17 21:12 ` Emanuel Berg
[not found] ` <mailman.519.1445115776.7904.help-gnu-emacs@gnu.org>
2015-10-18 1:08 ` Pascal J. Bourguignon
[not found] ` <mailman.432.1444964227.7904.help-gnu-emacs@gnu.org>
2015-10-16 3:57 ` Pascal J. Bourguignon
2015-10-16 4:17 ` Random832
[not found] ` <mailman.434.1444970033.7904.help-gnu-emacs@gnu.org>
2015-10-16 5:16 ` Pascal J. Bourguignon
[not found] ` <mailman.429.1444962165.7904.help-gnu-emacs@gnu.org>
2015-10-16 3:31 ` Pascal J. Bourguignon
2015-10-16 23:46 ` Emanuel Berg
[not found] ` <mailman.483.1445038647.7904.help-gnu-emacs@gnu.org>
2015-10-17 2:04 ` Pascal J. Bourguignon
2015-10-17 4:40 ` Random832
2015-10-17 5:00 ` Emanuel Berg
2015-10-17 4:40 ` Emanuel Berg
2015-10-17 5:56 ` Barry Margolin
2015-10-17 15:06 ` Emanuel Berg
[not found] ` <mailman.491.1445056308.7904.help-gnu-emacs@gnu.org>
2015-10-17 5:53 ` Barry Margolin
2015-10-17 15:16 ` Pascal J. Bourguignon
2015-10-17 21:06 ` Emanuel Berg
[not found] ` <mailman.518.1445115463.7904.help-gnu-emacs@gnu.org>
2015-10-18 1:07 ` Pascal J. Bourguignon
2015-10-18 12:32 ` Emanuel Berg
[not found] ` <mailman.551.1445171034.7904.help-gnu-emacs@gnu.org>
2015-10-18 12:55 ` Pascal J. Bourguignon
2015-10-18 14:28 ` Emanuel Berg
2015-10-18 21:17 ` Robert Thorpe
[not found] ` <mailman.557.1445177952.7904.help-gnu-emacs@gnu.org>
2015-10-18 19:48 ` Barry Margolin
2015-10-18 21:25 ` Emanuel Berg
2015-10-18 21:39 ` Random832
2015-10-19 0:46 ` Pascal J. Bourguignon
2015-10-16 13:32 ` Barry Margolin
2015-10-16 23:47 ` Emanuel Berg
[not found] <mailman.581.1445203060.7904.help-gnu-emacs@gnu.org>
2015-10-19 0:45 ` Pascal J. Bourguignon
2015-10-16 1:12 Emanuel Berg
2015-10-17 1:11 ` Aurélien Aptel
2015-10-17 4:22 ` Emanuel Berg
2015-10-17 7:58 ` Jude DaShiell
2015-10-19 16:33 ` Nick Dokos
[not found] ` <mailman.490.1445055179.7904.help-gnu-emacs@gnu.org>
2015-10-17 15:09 ` Pascal J. Bourguignon
[not found] ` <mailman.488.1445044303.7904.help-gnu-emacs@gnu.org>
2015-10-17 2:22 ` Pascal J. Bourguignon
2015-10-17 4:56 ` Emanuel Berg
2015-10-17 5:49 ` Barry Margolin
2015-10-17 15:04 ` Emanuel Berg
[not found] ` <mailman.506.1445093727.7904.help-gnu-emacs@gnu.org>
2015-10-17 15:20 ` Pascal J. Bourguignon
2015-10-17 15:38 ` Emanuel Berg
[not found] ` <mailman.511.1445095810.7904.help-gnu-emacs@gnu.org>
2015-10-17 16:01 ` Javier
2015-10-17 16:03 ` Javier
2015-10-17 16:34 ` Pascal J. Bourguignon
2015-10-17 21:18 ` Emanuel Berg
2015-10-17 16:15 ` Pascal J. Bourguignon
2015-10-17 21:37 ` Emanuel Berg
2015-10-17 15:18 ` Pascal J. Bourguignon
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