48 lines
61 KiB
HTML
48 lines
61 KiB
HTML
|
<!doctype html>
|
|||
|
|
<html lang="en" dir="ltr" class="docs-wrapper plugin-docs plugin-id-default docs-version-current docs-doc-page docs-doc-id-chap-3/d-i-dictionary/load-time-value_special-operator" data-has-hydrated="false">
|
|||
|
|
<head>
|
|||
|
|
<meta charset="UTF-8">
|
|||
|
|
<meta name="generator" content="Docusaurus v3.0.1">
|
|||
|
|
<title data-rh="true">load-time-value | Common Lisp (New) Language Reference</title><meta data-rh="true" name="viewport" content="width=device-width,initial-scale=1"><meta data-rh="true" name="twitter:card" content="summary_large_image"><meta data-rh="true" property="og:image" content="https://lisp-docs.github.io/cl-language-reference/img/1024px-Lisp_logo.svg.png"><meta data-rh="true" name="twitter:image" content="https://lisp-docs.github.io/cl-language-reference/img/1024px-Lisp_logo.svg.png"><meta data-rh="true" property="og:url" content="https://lisp-docs.github.io/cl-language-reference/chap-3/d-i-dictionary/load-time-value_special-operator"><meta data-rh="true" property="og:locale" content="en"><meta data-rh="true" name="docusaurus_locale" content="en"><meta data-rh="true" name="docsearch:language" content="en"><meta data-rh="true" name="google-site-verification" content="Vzaw013_bfdKeUVG89Ch3W1zC9_vH9ID2dPB9Dz0vr0"><meta data-rh="true" name="docusaurus_version" content="current"><meta data-rh="true" name="docusaurus_tag" content="docs-default-current"><meta data-rh="true" name="docsearch:version" content="current"><meta data-rh="true" name="docsearch:docusaurus_tag" content="docs-default-current"><meta data-rh="true" property="og:title" content="load-time-value | Common Lisp (New) Language Reference"><meta data-rh="true" name="description" content="Expanded Reference: load-time-value"><meta data-rh="true" property="og:description" content="Expanded Reference: load-time-value"><link data-rh="true" rel="icon" href="../../img/favicon.ico"><link data-rh="true" rel="canonical" href="load-time-value_special-operator.html"><link data-rh="true" rel="alternate" href="load-time-value_special-operator.html" hreflang="en"><link data-rh="true" rel="alternate" href="load-time-value_special-operator.html" hreflang="x-default"><link data-rh="true" rel="preconnect" href="https://C1F2Q5VM6X-dsn.algolia.net" crossorigin="anonymous"><link rel="preconnect" href="https://www.google-analytics.com">
|
|||
|
|
<link rel="preconnect" href="https://www.googletagmanager.com">
|
|||
|
|
<script async src="https://www.googletagmanager.com/gtag/js?id=G-8TJCE4NSF8"></script>
|
|||
|
|
<script>function gtag(){dataLayer.push(arguments)}window.dataLayer=window.dataLayer||[],gtag("js",new Date),gtag("config","G-8TJCE4NSF8",{})</script>
|
|||
|
|
|
|||
|
|
|
|||
|
|
<link rel="search" type="application/opensearchdescription+xml" title="Common Lisp (New) Language Reference" href="../../opensearch.xml"><link rel="stylesheet" href="../../assets/css/styles.f13b59fe.css">
|
|||
|
|
<script src="../../assets/js/runtime~main.02699c25.js" defer="defer"></script>
|
|||
|
|
<script src="../../assets/js/main.4f0a7a76.js" defer="defer"></script>
|
|||
|
|
</head>
|
|||
|
|
<body class="navigation-with-keyboard">
|
|||
|
|
<script>!function(){function t(t){document.documentElement.setAttribute("data-theme",t)}var e=function(){try{return new URLSearchParams(window.location.search).get("docusaurus-theme")}catch(t){}}()||function(){try{return localStorage.getItem("theme")}catch(t){}}();t(null!==e?e:"light")}(),function(){try{const c=new URLSearchParams(window.location.search).entries();for(var[t,e]of c)if(t.startsWith("docusaurus-data-")){var a=t.replace("docusaurus-data-","data-");document.documentElement.setAttribute(a,e)}}catch(t){}}()</script><div id="__docusaurus"><div role="region" aria-label="Skip to main content"><a class="skipToContent_fXgn" href="load-time-value_special-operator.html#__docusaurus_skipToContent_fallback">Skip to main content</a></div><nav aria-label="Main" class="navbar navbar--fixed-top"><div class="navbar__inner"><div class="navbar__items"><button aria-label="Toggle navigation bar" aria-expanded="false" class="navbar__toggle clean-btn" type="button"><svg width="30" height="30" viewBox="0 0 30 30" aria-hidden="true"><path stroke="currentColor" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2" d="M4 7h22M4 15h22M4 23h22"></path></svg></button><a href="../../../index.html" target="_blank" rel="noopener noreferrer" class="navbar__brand"><div class="navbar__logo"><img src="../../img/logo.svg" alt="Lisp Logo" class="themedComponent_mlkZ themedComponent--light_NVdE"><img src="../../img/logo.svg" alt="Lisp Logo" class="themedComponent_mlkZ themedComponent--dark_xIcU"></div><b class="navbar__title text--truncate">Common Lisp Docs</b></a><a href="../../../docs/tutorial/index.html" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link">Tutorial</a><a href="../../index.html" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link">Technical Reference</a><a href="../../../docs/whylisp.html" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link">Why Lisp?</a><a href="../../../docs/howto.html" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link">Guides</a></div><div class="navbar__items navbar__items--right"><a href="../../../docs/contribute.html" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link">Contribute!</a><a href="../../../docs/help.html" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link">Getting Help</a><a href="../../../docs/about.html" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link">About</a><a href="../../../blog.html" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link">Blog</a><a href="https://github.com/lisp-docs" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link">GitHub<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><div class="toggle_vylO colorModeToggle_DEke"><button class="clean-btn toggleButton_gllP toggleButtonDisabled_aARS" type="button" disabled="" title="Switch between dark and light mode (currently light mode)" aria-label="Switch between dark and light mode (currently light mode)" aria-live="polite"><svg viewBox="0 0 24 24" width="24" height="24" class="lightToggleIcon_pyhR"><path fill="currentColor" d="M12,9c1.65,0,3,1.35,3,3s-1.35,3-3,3s-3-1.35-3-3S10.35,9,12,9 M12,7c-2.76,0-5,2.24-5,5s2.24,5,5,5s5-2.24,5-5 S14.76,7,12,7L12,7z M2,13l2,0c0.55,0,1-0.45,1-1s-0.45-1-1-1l-2,0c-0.55,0-1,0.45-1,1S1.45,13,2,13z M20,13l2,0c0.55,0,1-0.45,1-1 s-0.45-1-1-1l-2,0c-0.55,0-1,0.45-1,1S19.45,13,20,13z M11,2v2c0,0.55,0.45,1,1,1s1-0.45,1-1V2c0-0.55-0.45-1-1-1S11,1.45,11,2z M11,20v2c0,0.55,0.45,1,1,1s1-0.45,1-1v-2c0-0.55-0.45-1-1-1C11.45,19,11,19.45,11,20z M5.99,4.58c-0.39-0.39-1.03-0.39-1.41,0 c-0.39,0.39-0.39,1.03,0,1.41l1.06,1.06c0.39,0.39,1.03,0.39,1.41,0s0.39-1.03,0-1.41L5.99,4.58z M18.36,16.95 c-0.39-0.39-1.03-0.39-1.41,0c-0.39,0.39-0.39,1.03,0,1.41l1.06,1.06c0.39,0.39,1.03,0.39,1.41,0c0.39-0
|
|||
|
|
<!-- -->
|
|||
|
|
<!-- -->
|
|||
|
|
<p><strong>load-time-value</strong> <span><i>Special Operator</i></span></p>
|
|||
|
|
<p><strong>Syntax:</strong></p>
|
|||
|
|
<p><span><b>load-time-value</b></span> <span><i>form</i></span> &optional <em>read-only-p → object</em></p>
|
|||
|
|
<p><strong>Arguments and Values:</strong></p>
|
|||
|
|
<p><span><i>form</i></span>—a <span><i>form</i></span>; evaluated as described below.</p>
|
|||
|
|
<p><em>read-only-p</em>—a <span><i>boolean</i></span>; not evaluated.</p>
|
|||
|
|
<p><span><i>object</i></span>—the <span><i>primary value</i></span> resulting from evaluating <span><i>form</i></span>.</p>
|
|||
|
|
<p><strong>Description:</strong></p>
|
|||
|
|
<p><span><b>load-time-value</b></span> provides a mechanism for delaying evaluation of <span><i>form</i></span> until the expression is in the run-time environment; see Section 3.2 (Compilation).</p>
|
|||
|
|
<p><em>Read-only-p</em> designates whether the result can be considered a <span><i>constant object</i></span>. If <span><b>t</b></span>, the result is a read-only quantity that can, if appropriate to the <span><i>implementation</i></span>, be copied into read-only space and/or <em>coalesced</em> with <em>similar constant objects</em> from other <span><i>programs</i></span>. If <span><b>nil</b></span> (the default), the result must be neither copied nor coalesced; it must be considered to be potentially modifiable data.</p>
|
|||
|
|
<p>If a <span><b>load-time-value</b></span> expression is processed by <span><b>compile-file</b></span>, the compiler performs its normal semantic processing (such as macro expansion and translation into machine code) on <span><i>form</i></span>, but arranges for the execution of <span><i>form</i></span> to occur at load time in a <span><i>null lexical environment</i></span>, with the result of this <span><i>evaluation</i></span> then being treated as a <em>literal object</em> at run time. It is guaranteed that</p>
|
|||
|
|
<p>the evaluation of <span><i>form</i></span> will take place only once when the <span><i>file</i></span> is <em>loaded</em>, but the order of evaluation with respect to the evaluation of <span><i>top level forms</i></span> in the file is <span><i>implementation-dependent</i></span>.</p>
|
|||
|
|
<p>If a <span><b>load-time-value</b></span> expression appears within a function compiled with <span><b>compile</b></span>, the <span><i>form</i></span> is evaluated at compile time in a <span><i>null lexical environment</i></span>. The result of this compile-time evaluation is treated as a <em>literal object</em> in the compiled code.</p>
|
|||
|
|
<span><b>load-time-value</b></span>
|
|||
|
|
<p>If a <span><b>load-time-value</b></span> expression is processed by <span><b>eval</b></span>, <span><i>form</i></span> is evaluated in a <span><i>null lexical environment</i></span>, and one value is returned. Implementations that implicitly compile (or partially compile) expressions processed by <span><b>eval</b></span> might evaluate <span><i>form</i></span> only once, at the time this compilation is performed.</p>
|
|||
|
|
<p>If the <em>same list</em> (load-time-value <span><i>form</i></span>) is evaluated or compiled more than once, it is <span><i>implementation-dependent</i></span> whether <span><i>form</i></span> is evaluated only once or is evaluated more than once. This can happen both when an expression being evaluated or compiled shares substructure, and when the <em>same form</em> is processed by <span><b>eval</b></span> or <span><b>compile</b></span> multiple times. Since a <span><b>load-time-value</b></span> expression can be referenced in more than one place and can be evaluated multiple times by <span><b>eval</b></span>, it is <span><i>implementation-dependent</i></span> whether each execution returns a fresh <span><i>object</i></span> or returns the same <span><i>object</i></span> as some other execution. Users must use caution when destructively modifying the resulting <span><i>object</i></span>.</p>
|
|||
|
|
<p>If two lists (load-time-value <span><i>form</i></span>) that are the <span><i>same</i></span> under <span><b>equal</b></span> but are not <span><i>identical</i></span> are evaluated or compiled, their values always come from distinct evaluations of <span><i>form</i></span>. Their <span><i>values</i></span> may not be coalesced unless <em>read-only-p</em> is <span><b>t</b></span>.</p>
|
|||
|
|
<p><strong>Examples:</strong></p>
|
|||
|
|
<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 heading comment title" style="color:#999988;font-style:italic">;;; The function INCR1 always returns the same value, even in different images. ;;; The function INCR2 always returns the same value in a given image, </span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token heading comment title" style="color:#999988;font-style:italic">;;; but the value it returns might vary from image to image. </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 defun keyword" style="color:#00009f">defun</span><span class="token defun"> </span><span class="token defun function" style="color:#d73a49">incr1</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><span class="token punctuation" style="color:#393A34">(</span><span class="token car">+</span><span class="token plain"> x #.</span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">random</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">17</span><span class="token punctuation" style="color:#393A34">)</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 defun keyword" style="color:#00009f">defun</span><span class="token defun"> </span><span class="token defun function" style="color:#d73a49">incr2</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><span class="token punctuation" style="color:#393A34">(</span><span class="token car">+</span><span class="token plain"> x </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">load-time-value</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">random</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">17</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</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 heading comment title" style="color:#999988;font-style:italic">;;; The function FOO1-REF references the nth element of the first of </span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token heading comment title" style="color:#999988;font-style:italic">;;; the \*FOO-ARRAYS\* that is available at load time. It is permissible for </span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></spa
|
|||
|
|
<p><strong>See Also:</strong></p>
|
|||
|
|
<p><span><b>compile-file</b></span>, <span><b>compile</b></span>, <span><b>eval</b></span>, Section 3.2.2.2 (Minimal Compilation), Section 3.2 (Compilation)</p>
|
|||
|
|
<p><strong>Notes:</strong></p>
|
|||
|
|
<p><span><b>load-time-value</b></span> must appear outside of quoted structure in a “for <span><i>evaluation</i></span>” position. In situations which would appear to call for use of <span><b>load-time-value</b></span> within a quoted structure, the <em>backquote reader macro</em> is probably called for; see Section 2.4.6 (Backquote).</p>
|
|||
|
|
<p>Specifying <span><b>nil</b></span> for <em>read-only-p</em> is not a way to force an object to become modifiable if it has already been made read-only. It is only a way to say that, for an object that is modifiable, this operation is not intended to make that object read-only.</p>
|
|||
|
|
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="expanded-reference-load-time-value">Expanded Reference: load-time-value<a href="load-time-value_special-operator.html#expanded-reference-load-time-value" class="hash-link" aria-label="Direct link to Expanded Reference: load-time-value" title="Direct link to Expanded Reference: load-time-value"></a></h2>
|
|||
|
|
<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>
|
|||
|
|
<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 car">load-time-value</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-3/d-i-dictionary/load-time-value_special-operator.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="lambda_symbol.html"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">lambda</div></a><a class="pagination-nav__link pagination-nav__link--next" href="locally_special-operator.html"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">locally</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="load-time-value_special-operator.html#expanded-reference-load-time-value" class="table-of-contents__link toc-highlight">Expanded Reference: load-time-value</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.
|
|||
|
|
</body>
|
|||
|
|
</html>
|