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menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-1/b-b-scope-purpose-and-history.html">1. Introduction</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-2/c-b-character-syntax.html">2. Syntax</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret menu__link--active" aria-expanded="true" href="../d-b-evaluation.html">3. 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href="../d-f-error-checking-in-function-calls.html">3.5 Error Checking in Function Calls</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="../d-g-traversal-rules-and-side-effects.html">3.6 Traversal Rules and Side Effects</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="../d-h-destructive-operations.html">3.7 Destructive Operations</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-2 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--active" aria-expanded="true" tabindex="0" href="../../category/38-evaluation-and-compilation-dictionary.html">3.8 Evaluation and Compilation Dictionary</a><button aria-label="Collapse sidebar category '3.8 Evaluation and Compilation Dictionary'" type="button" class="clean-btn 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href="macroexpand_macroexpand-1_function.html">macroexpand, macroexpand-1</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="optimize_declaration.html">optimize</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="proclaim_function.html">proclaim</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="quote_special-operator.html">quote</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="special-operator-p_function.html">special-operator-p</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="special_declaration.html">special</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="symbol-macrolet_special-operator.html">symbol-macrolet</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="the_special-operator.html">the</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="type_declaration.html">type</a></li></ul></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-4/e-b-introduction.html">4. Types and Classes</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-5/f-b-generalized-reference.html">5. Data and Control Flow</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-6/g-b-the-loop-facility.html">6. Iteration</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-7/h-b-object-creation-and-initialization.html">7. Objects</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../category/81-structures-dictionary.html">8. Structures</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-9/j-b-condition-system-concepts.html">9. Conditions</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-10/ba-b-symbol-concepts.html">10. Symbols</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-11/bb-b-package-concepts.html">11. Packages</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-12/bc-b-number-concepts.html">12. Numbers</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-13/bd-b-character-concepts.html">13. Characters</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-14/be-b-cons-concepts.html">14. Conses</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-15/bf-b-array-concepts.html">15. Arrays</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-16/bg-b-string-concepts.html">16. Strings</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-17/bh-b-sequence-concepts.html">17. Sequences</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-18/bi-b-hash-table-concepts.html">18. Hash Tables</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-19/bj-b-overview-of-filenames.html">19. Filenames</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-20/ca-b-file-system-concepts.html">20. Files</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-21/cb-b-stream-concepts.html">21. Streams</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-22/cc-b-the-lisp-printer.html">22. Printer</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-23/cd-b-reader-concepts.html">23. Reader</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-24/ce-b-system-construction-concepts.html">24. System Construction</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-25/cf-b-the-external-environment.html">25. External Environment</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../environments.html">26. Environments</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../meta-object-protocol.html">27. Meta Object Protocol</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../data-structures.html">28. Data Structures</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../portability/trivial-packages.html">29. Portability</a></div></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-1 menu__list-item"><a class="menu__link" href="../../dictionary-entries.html">dictionary-entries</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="../../chap-26/intro.html">Glossary</a></div></li></ul></nav></div></div></aside><main class="docMainContainer_TBSr"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Z_bl" aria-label="Breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a aria-label="Home page" class="breadcrumbs__link" href="../../index.html"><svg viewBox="0 0 24 24" class="breadcrumbHomeIcon_YNFT"><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">3. Evaluation and Compilation</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item"><a class="breadcrumbs__link" itemprop="item" href="../../category/38-evaluation-and-compilation-dictionary.html"><span itemprop="name">3.8 Evaluation and Compilation Dictionary</span></a><meta itemprop="position" content="2"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">load-time-value</span><meta itemprop="position" content="3"></li></ul></nav><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><h1>load-time-value</h1>
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<p><strong>load-time-value</strong> <span><i>Special Operator</i></span></p>
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<p><strong>Syntax:</strong></p>
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<p><span><b>load-time-value</b></span> <span><i>form</i></span> &optional <em>read-only-p → object</em></p>
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<p><strong>Arguments and Values:</strong></p>
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<p><span><i>form</i></span>—a <span><i>form</i></span>; evaluated as described below.</p>
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<p><em>read-only-p</em>—a <span><i>boolean</i></span>; not evaluated.</p>
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<p><span><i>object</i></span>—the <span><i>primary value</i></span> resulting from evaluating <span><i>form</i></span>.</p>
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<p><strong>Description:</strong></p>
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<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>
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<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>
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<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>
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<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>
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<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>
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<span><b>load-time-value</b></span>
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<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>
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<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>
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<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>
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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 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"></span><span class="token heading comment title" style="color:#999988;font-style:italic">;;; that array to be modified (e.g., by SET-FOO1-REF); FOO1-REF will see the </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">;;; updated values. </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 car">defvar</span><span class="token plain"> \*foo-arrays\* </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">list</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">make-array</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">7</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">make-array</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">8</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">foo1-ref</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">n</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">aref</span><span class="token plain"> </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">first</span><span class="token plain"> \*my-arrays\*</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token boolean" style="color:#36acaa">nil</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> n</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">set-foo1-ref</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">n</span><span class="token defun arguments"> </span><span class="token defun arguments argument variable" style="color:#36acaa">val</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 car">setf</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">aref</span><span class="token plain"> </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">first</span><span class="token plain"> \*my-arrays\*</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token boolean" style="color:#36acaa">nil</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> n</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> val</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 BAR1-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 \*BAR-ARRAYS\* that is available at load time. The programmer has </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">;;; promised that the array will be treated as read-only, so the system </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">;;; can copy or coalesce the array. </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 car">defvar</span><span class="token plain"> \*bar-arrays\* </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">list</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">make-array</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">7</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">make-array</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">8</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">bar1-ref</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">n</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">aref</span><span class="token plain"> </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">first</span><span class="token plain"> \*my-arrays\*</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token boolean" style="color:#36acaa">t</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> n</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">;;; This use of LOAD-TIME-VALUE permits the indicated vector to be coalesced </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">;;; even though NIL was specified, because the object was already read-only </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">;;; when it was written as a literal vector rather than created by a constructor. ;;; User programs must treat the vector v as read-only. </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">baz-ref</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">n</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">let</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 car">v</span><span class="token plain"> </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">A</span><span class="token plain"> B C</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token boolean" style="color:#36acaa">nil</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 car">values</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">svref</span><span class="token plain"> v n</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> v</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">;;; This use of LOAD-TIME-VALUE permits the indicated vector to be coalesced </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">;;; even though NIL was specified in the outer situation because T was specified ;;; in the inner situation. User programs must treat the vector v as read-only. (defun baz-ref (n) </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">let</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 car">v</span><span class="token plain"> </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">load-time-value</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">vector</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">2</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">3</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token boolean" style="color:#36acaa">t</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token boolean" style="color:#36acaa">nil</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 car">values</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token car">svref</span><span class="token plain"> v n</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> v</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></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>
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<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>
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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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