From: <tomas@tuxteam.de>
To: help-gnu-emacs@gnu.org
Subject: Re: Lisp Live buffer
Date: Wed, 28 Dec 2022 10:25:24 +0100 [thread overview]
Message-ID: <Y6wLhGQo6kn1J0LN@tuxteam.de> (raw)
In-Reply-To: <878rismkp7.fsf@dataswamp.org>
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On Wed, Dec 28, 2022 at 01:32:52AM +0100, Emanuel Berg wrote:
> Why doesn't this work?
>
> For sure, there is a mistake somewhere but it seems now matter how
> I change it I get the same result ...
>
> ;;; -*- lexical-binding: t -*-
> ;;
> ;; this file:
> ;; https://dataswamp.org/~incal/emacs-init/mvc/model.el
>
> (require 'cl-lib)
>
> (defun make-world (dim len &optional init)
> (or init (setq init "."))
> (if (zerop dim)
> init
> (make-list len (make-world (1- dim) len init)) ))
Heh. When you are making a higher-order world, you are
storing a ref to the same list in each of its slots.
So if you change something at a lower level *poof*
all are changed. Read the subsection "samenes and change"
in 3.1 of SICP [1] for a beautiful treatment (actually,
re-read SICP: a beautiful book)
Oh, I nearly forgot: if you want it to work, you'll
have to regenerate the lower-level worlds (or deep
copy them).
Cheers
[1] https://mitp-content-server.mit.edu/books/content/sectbyfn/books_pres_0/6515/sicp.zip/full-text/book/book-Z-H-20.html
(Sorry: fragment links seem to be disfunctional)
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next prev parent reply other threads:[~2022-12-28 9:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-06 15:44 Lisp Live buffer Emanuel Berg
2022-12-07 3:06 ` Jean Louis
2022-12-07 3:54 ` Emanuel Berg
2022-12-23 8:15 ` Jean Louis
2022-12-26 20:26 ` Emanuel Berg
2022-12-27 1:12 ` Emanuel Berg
2022-12-28 0:32 ` Emanuel Berg
2022-12-28 2:04 ` Emanuel Berg
2022-12-28 2:08 ` Emanuel Berg
2022-12-28 9:25 ` tomas [this message]
2022-12-28 19:53 ` Emanuel Berg
2022-12-28 23:20 ` Emanuel Berg
2022-12-08 11:32 ` Madhu
2022-12-23 8:23 ` Jean Louis
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