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diff --git a/devdocs/elisp/setcar.html b/devdocs/elisp/setcar.html deleted file mode 100644 index 67867eb1..00000000 --- a/devdocs/elisp/setcar.html +++ /dev/null @@ -1,70 +0,0 @@ - <h4 class="subsection">Altering List Elements with setcar</h4> <p>Changing the <small>CAR</small> of a cons cell is done with <code>setcar</code>. When used on a list, <code>setcar</code> replaces one element of a list with a different element. </p> <dl> <dt id="setcar">Function: <strong>setcar</strong> <em>cons object</em> -</dt> <dd> -<p>This function stores <var>object</var> as the new <small>CAR</small> of <var>cons</var>, replacing its previous <small>CAR</small>. In other words, it changes the <small>CAR</small> slot of <var>cons</var> to refer to <var>object</var>. It returns the value <var>object</var>. For example: </p> <div class="example"> <pre class="example">(setq x (list 1 2)) - ⇒ (1 2) -</pre> -<pre class="example">(setcar x 4) - ⇒ 4 -</pre> -<pre class="example">x - ⇒ (4 2) -</pre> -</div> </dd> -</dl> <p>When a cons cell is part of the shared structure of several lists, storing a new <small>CAR</small> into the cons changes one element of each of these lists. Here is an example: </p> <div class="example"> <pre class="example">;; <span class="roman">Create two lists that are partly shared.</span> -(setq x1 (list 'a 'b 'c)) - ⇒ (a b c) -(setq x2 (cons 'z (cdr x1))) - ⇒ (z b c) -</pre> - -<pre class="example">;; <span class="roman">Replace the CAR of a shared link.</span> -(setcar (cdr x1) 'foo) - ⇒ foo -x1 ; <span class="roman">Both lists are changed.</span> - ⇒ (a foo c) -x2 - ⇒ (z foo c) -</pre> - -<pre class="example">;; <span class="roman">Replace the CAR of a link that is not shared.</span> -(setcar x1 'baz) - ⇒ baz -x1 ; <span class="roman">Only one list is changed.</span> - ⇒ (baz foo c) -x2 - ⇒ (z foo c) -</pre> -</div> <p>Here is a graphical depiction of the shared structure of the two lists in the variables <code>x1</code> and <code>x2</code>, showing why replacing <code>b</code> changes them both: </p> <div class="example"> <pre class="example"> --- --- --- --- --- --- -x1---> | | |----> | | |--> | | |--> nil - --- --- --- --- --- --- - | --> | | - | | | | - --> a | --> b --> c - | - --- --- | -x2--> | | |-- - --- --- - | - | - --> z -</pre> -</div> <p>Here is an alternative form of box diagram, showing the same relationship: </p> <div class="example"> <pre class="example">x1: - -------------- -------------- -------------- -| car | cdr | | car | cdr | | car | cdr | -| a | o------->| b | o------->| c | nil | -| | | -->| | | | | | - -------------- | -------------- -------------- - | -x2: | - -------------- | -| car | cdr | | -| z | 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/Setcar.html" class="_attribution-link">https://www.gnu.org/software/emacs/manual/html_node/elisp/Setcar.html</a> - </p> -</div> |