91 lines
3.9 KiB
HTML
91 lines
3.9 KiB
HTML
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>Eval Literal (Guile Reference Manual)</title>
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<div class="subsubsection-level-extent" id="Eval-Literal">
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<p>
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Next: <a href="Eval-Variable.html" accesskey="n" rel="next">Evaluating a Variable Reference</a>, Up: <a href="Evaluating.html" accesskey="u" rel="up">Evaluating Expressions and Executing Programs</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<hr>
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<h4 class="subsubsection" id="Evaluating-Literal-Data"><span>3.3.1.1 Evaluating Literal Data<a class="copiable-link" href="#Evaluating-Literal-Data"> ¶</a></span></h4>
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<p>When a literal data expression is evaluated, the value of the expression
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is simply the value that the expression describes. The evaluation of a
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literal data expression has no side effects.
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</p>
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<p>So, for example,
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</p>
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<ul class="itemize mark-bullet">
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<li>the value of the expression <code class="code">"abc"</code> is the string value
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<code class="code">"abc"</code>
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</li><li>the value of the expression <code class="code">3+4i</code> is the complex number 3 + 4i
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</li><li>the value of the expression <code class="code">#(1 2 3)</code> is a three-element vector
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containing the numeric values 1, 2 and 3.
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</li></ul>
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<p>For any data type which can be expressed literally like this, the syntax
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of the literal data expression for that data type — in other words,
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what you need to write in your code to indicate a literal value of that
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type — is known as the data type’s <em class="dfn">read syntax</em>. This manual
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specifies the read syntax for each such data type in the section that
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describes that data type.
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</p>
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<p>Some data types do not have a read syntax. Procedures, for example,
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cannot be expressed as literal data; they must be created using a
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<code class="code">lambda</code> expression (see <a class="pxref" href="Creating-a-Procedure.html">Creating and Using a New Procedure</a>) or implicitly
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using the shorthand form of <code class="code">define</code> (see <a class="pxref" href="Lambda-Alternatives.html">Lambda Alternatives</a>).
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</p>
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