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<!-- -->
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<p><strong>error</strong> <span><i>Function</i></span></p>
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<p><strong>Syntax:</strong></p>
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<p><span><b>error</b></span> <em>datum</em> &rest <em>arguments →</em></p>
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<p><strong>Arguments and Values:</strong></p>
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<p><em>datum</em>, <span><i>arguments</i></span>—<span><i>designators</i></span> for a <span><i>condition</i></span> of default type <span><b>simple-error</b></span>.</p>
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<p><strong>Description:</strong></p>
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<p><span><b>error</b></span> effectively invokes <span><b>signal</b></span> on the denoted <span><i>condition</i></span>.</p>
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<p>If the <span><i>condition</i></span> is not handled, (invoke-debugger <span><i>condition</i></span>) is done. As a consequence of calling <span><b>invoke-debugger</b></span>, <span><b>error</b></span> cannot directly return; the only exit from <span><b>error</b></span> can come by non-local transfer of control in a handler or by use of an interactive debugging command.</p>
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<p><strong>Examples:</strong></p>
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<div class="language-lisp codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-lisp codeBlock_bY9V thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token punctuation" style="color:#393A34">(</span><span class="token defun keyword" style="color:#00009f">defun</span><span class="token defun"> </span><span class="token defun function" style="color:#d73a49">factorial</span><span class="token defun"> </span><span class="token defun punctuation" style="color:#393A34">(</span><span class="token defun arguments argument variable" style="color:#36acaa">x</span><span class="token defun punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">cond</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">or</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">not</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">typep</span><span class="token plain"> x ’integer</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">minusp</span><span class="token plain"> x</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">error</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"~</span><span class="token string argument" style="color:#e3116c">S</span><span class="token string" style="color:#e3116c"> is not a valid argument to </span><span class="token string argument" style="color:#e3116c">FACTORIAL</span><span class="token string" style="color:#e3116c">."</span><span class="token plain"> x</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">zerop</span><span class="token plain"> x</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> **error** </span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token boolean" style="color:#36acaa">t</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">\* x </span><span class="tok
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<p><strong>Side Effects:</strong></p>
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<p><span><i>Handlers</i></span> for the specified condition, if any, are invoked and might have side effects. Program execution might stop, and the debugger might be entered.</p>
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<p><strong>Affected By:</strong></p>
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<p>Existing handler bindings.</p>
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<span><b>*break-on-signals*</b></span>
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<p>Signals an error of <span><i>type</i></span> <span><b>type-error</b></span> if <em>datum</em> and <span><i>arguments</i></span> are not <span><i>designators</i></span> for a <span><i>condition</i></span>.</p>
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<p><strong>See Also:</strong></p>
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<p><span><b>cerror</b></span>, <span><b>signal</b></span>, <span><b>format</b></span>, <span><b>ignore-errors</b></span>, <span><b>*break-on-signals*</b></span>, <span><b>handler-bind</b></span>, Section 9.1 (Condition</p>
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<p>System Concepts)</p>
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<p><strong>Notes:</strong></p>
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<p>Some implementations may provide debugger commands for interactively returning from individual stack frames. However, it should be possible for the programmer to feel confident about writing code like:</p>
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<p>(defun wargames<!-- -->:no-win-scenario<!-- --> ()</p>
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<p>(if (error "pushing the button would be stupid."))</p>
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<p>(push-the-button))</p>
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<p>In this scenario, there should be no chance that <span><b>error</b></span> will return and the button will get pushed.</p>
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<p>While the meaning of this program is clear and it might be proven ‘safe’ by a formal theorem prover, such a proof is no guarantee that the program is safe to execute. Compilers have been known to have bugs, computers to have signal glitches, and human beings to manually intervene in ways that are not always possible to predict. Those kinds of errors, while beyond the scope of the condition system to formally model, are not beyond the scope of things that should seriously be considered when writing code that could have the kinds of sweeping effects hinted at by this example.</p>
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<h2 class="anchor anchorWithStickyNavbar_LWe7" id="expanded-reference-error">Expanded Reference: error<a href="error_function.html#expanded-reference-error" class="hash-link" aria-label="Direct link to Expanded Reference: error" title="Direct link to Expanded Reference: error"></a></h2>
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<div class="theme-admonition theme-admonition-tip admonition_xJq3 alert alert--success"><div class="admonitionHeading_Gvgb"><span class="admonitionIcon_Rf37"><svg viewBox="0 0 12 16"><path fill-rule="evenodd" d="M6.5 0C3.48 0 1 2.19 1 5c0 .92.55 2.25 1 3 1.34 2.25 1.78 2.78 2 4v1h5v-1c.22-1.22.66-1.75 2-4 .45-.75 1-2.08 1-3 0-2.81-2.48-5-5.5-5zm3.64 7.48c-.25.44-.47.8-.67 1.11-.86 1.41-1.25 2.06-1.45 3.23-.02.05-.02.11-.02.17H5c0-.06 0-.13-.02-.17-.2-1.17-.59-1.83-1.45-3.23-.2-.31-.42-.67-.67-1.11C2.44 6.78 2 5.65 2 5c0-2.2 2.02-4 4.5-4 1.22 0 2.36.42 3.22 1.19C10.55 2.94 11 3.94 11 5c0 .66-.44 1.78-.86 2.48zM4 14h5c-.23 1.14-1.3 2-2.5 2s-2.27-.86-2.5-2z"></path></svg></span>tip</div><div class="admonitionContent_BuS1"><p>TODO: Please contribute to this page by adding explanations and examples</p></div></div>
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<div class="language-lisp codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-lisp codeBlock_bY9V thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">error</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">)</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://github.com/lisp-docs/cl-language-reference/tree/main/docs/chap-9/j-c-dictionary/error_function.md" target="_blank" rel="noopener noreferrer" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 40" class="iconEdit_Z9Sw" aria-hidden="true"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 3.1-3q0.5-0.5 1.2-0.5t1.1 0.5l3.9 3.9q0.5 0.4 0.5 1.1t-0.5 1.2z m-29.5 17.1l18.4-18.5 6.3 6.3-18.4 18.4h-6.3v-6.2z"></path></g></svg>Edit this page</a></div><div class="col lastUpdated_vwxv"><span class="theme-last-updated">Last updated<!-- --> by <b>daninus14</b></span></div></div></footer></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages"><a class="pagination-nav__link pagination-nav__link--prev" href="error_condition-type.html"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">error</div></a><a class="pagination-nav__link pagination-nav__link--next" href="find-restart_function.html"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">find-restart</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="error_function.html#expanded-reference-error" class="table-of-contents__link toc-highlight">Expanded Reference: error</a></li></ul></div></div></div></div></main></div></div></div><footer class="footer footer--dark"><div class="container container-fluid"><div class="row footer__links"><div class="col footer__col"><div class="footer__title">Docs</div><ul class="footer__items clean-list"><li class="footer__item"><a href="../../../docs/tutorial.html" target="_blank" rel="noopener noreferrer" class="footer__link-item">Common Lisp Tutorial</a></li><li class="footer__item"><a href="../../index.html" target="_blank" rel="noopener noreferrer" class="footer__link-item">Common Lisp Technical Reference</a></li><li class="footer__item"><a href="../../../docs/help.html" target="_blank" rel="noopener noreferrer" class="footer__link-item">Help</a></li></ul></div><div class="col footer__col"><div class="footer__title">Community</div><ul class="footer__items clean-list"><li class="footer__item"><a href="https://stackoverflow.com/questions/tagged/common-lisp" target="_blank" rel="noopener noreferrer" class="footer__link-item">Stack Overflow<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li class="footer__item"><a href="https://discord.gg/hhk46CE" target="_blank" rel=
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