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| author | Craig Jennings <c@cjennings.net> | 2025-08-14 22:58:58 -0500 |
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| committer | Craig Jennings <c@cjennings.net> | 2025-08-14 22:58:58 -0500 |
| commit | 82ba818ff456bcd6d56a06226e3f27e98fbb55c3 (patch) | |
| tree | 158cfc17b2f644a10f063cb546752cfaae12c97f /devdocs/elisp/setcdr.html | |
| parent | 9278ddd4ea1a8b1a4c1edaa8894516e3f48d245b (diff) | |
| download | dotemacs-82ba818ff456bcd6d56a06226e3f27e98fbb55c3.tar.gz dotemacs-82ba818ff456bcd6d56a06226e3f27e98fbb55c3.zip | |
removing all downloaded devdocs files
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| -rw-r--r-- | devdocs/elisp/setcdr.html | 53 |
1 files changed, 0 insertions, 53 deletions
diff --git a/devdocs/elisp/setcdr.html b/devdocs/elisp/setcdr.html deleted file mode 100644 index cd7fe80e..00000000 --- a/devdocs/elisp/setcdr.html +++ /dev/null @@ -1,53 +0,0 @@ - <h4 class="subsection">Altering the CDR of a List</h4> <p>The lowest-level primitive for modifying a <small>CDR</small> is <code>setcdr</code>: </p> <dl> <dt id="setcdr">Function: <strong>setcdr</strong> <em>cons object</em> -</dt> <dd><p>This function stores <var>object</var> as the new <small>CDR</small> of <var>cons</var>, replacing its previous <small>CDR</small>. In other words, it changes the <small>CDR</small> slot of <var>cons</var> to refer to <var>object</var>. It returns the value <var>object</var>. </p></dd> -</dl> <p>Here is an example of replacing the <small>CDR</small> of a list with a different list. All but the first element of the list are removed in favor of a different sequence of elements. The first element is unchanged, because it resides in the <small>CAR</small> of the list, and is not reached via the <small>CDR</small>. </p> <div class="example"> <pre class="example">(setq x (list 1 2 3)) - ⇒ (1 2 3) -</pre> -<pre class="example">(setcdr x '(4)) - ⇒ (4) -</pre> -<pre class="example">x - ⇒ (1 4) -</pre> -</div> <p>You can delete elements from the middle of a list by altering the <small>CDR</small>s of the cons cells in the list. For example, here we delete the second element, <code>b</code>, from the list <code>(a b c)</code>, by changing the <small>CDR</small> of the first cons cell: </p> <div class="example"> <pre class="example">(setq x1 (list 'a 'b 'c)) - ⇒ (a b c) -(setcdr x1 (cdr (cdr x1))) - ⇒ (c) -x1 - ⇒ (a c) -</pre> -</div> <p>Here is the result in box notation: </p> <div class="example"> <pre class="example"> -------------------- - | | - -------------- | -------------- | -------------- -| car | cdr | | | car | cdr | -->| car | cdr | -| a | o----- | b | o-------->| c | nil | -| | | | | | | | | - -------------- -------------- -------------- -</pre> -</div> <p>The second cons cell, which previously held the element <code>b</code>, still exists and its <small>CAR</small> is still <code>b</code>, but it no longer forms part of this list. </p> <p>It is equally easy to insert a new element by changing <small>CDR</small>s: </p> <div class="example"> <pre class="example">(setq x1 (list 'a 'b 'c)) - ⇒ (a b c) -(setcdr x1 (cons 'd (cdr x1))) - ⇒ (d b c) -x1 - ⇒ (a d b c) -</pre> -</div> <p>Here is this result in box notation: </p> <div class="example"> <pre class="example"> -------------- ------------- ------------- -| car | cdr | | car | cdr | | car | cdr | -| a | o | -->| b | o------->| c | nil | -| | | | | | | | | | | - --------- | -- | ------------- ------------- - | | - ----- -------- - | | - | --------------- | - | | car | cdr | | - -->| d | o------ - | | | - --------------- -</pre> -</div><div class="_attribution"> - <p class="_attribution-p"> - Copyright © 1990-1996, 1998-2022 Free Software Foundation, Inc. <br>Licensed under the GNU GPL license.<br> - <a href="https://www.gnu.org/software/emacs/manual/html_node/elisp/Setcdr.html" class="_attribution-link">https://www.gnu.org/software/emacs/manual/html_node/elisp/Setcdr.html</a> - </p> -</div> |