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227 lines
13 KiB
HTML
<!DOCTYPE html>
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<html>
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<meta http-equiv="Content-type" content="text/html;charset=UTF-8" />
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<title>Values – Wren</title>
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</head>
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<body id="top">
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<header>
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<div class="page">
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<div class="main-column">
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<h1><a href="./">wren</a></h1>
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<h2>a classy little scripting language</h2>
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</div>
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</div>
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</header>
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<div class="page">
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<nav class="big">
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<ul>
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<li><a href="getting-started.html">Getting Started</a></li>
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<li><a href="contributing.html">Contributing</a></li>
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</ul>
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<section>
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<h2>language guide</h2>
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<ul>
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<li><a href="syntax.html">Syntax</a></li>
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<li><a href="values.html">Values</a></li>
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<li><a href="lists.html">Lists</a></li>
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<li><a href="maps.html">Maps</a></li>
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<li><a href="method-calls.html">Method Calls</a></li>
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<li><a href="control-flow.html">Control Flow</a></li>
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<li><a href="variables.html">Variables</a></li>
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<li><a href="functions.html">Functions</a></li>
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<li><a href="classes.html">Classes</a></li>
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<li><a href="concurrency.html">Concurrency</a></li>
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<li><a href="error-handling.html">Error Handling</a></li>
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<li><a href="modularity.html">Modularity</a></li>
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</ul>
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</section>
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<section>
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<h2>reference</h2>
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<ul>
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<li><a href="modules">Modules</a></li>
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<li><a href="embedding">Embedding</a></li>
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<li><a href="performance.html">Performance</a></li>
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<li><a href="qa.html">Q & A</a></li>
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<td><a href="getting-started.html">Getting Started</a></td>
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<td><a href="contributing.html">Contributing</a></td>
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</tr>
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<tr>
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<td colspan="2"><h2>language guide</h2></td>
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<td><h2>reference</h2></td>
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</tr>
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<tr>
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<td>
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<ul>
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<li><a href="syntax.html">Syntax</a></li>
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<li><a href="values.html">Values</a></li>
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<li><a href="lists.html">Lists</a></li>
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<li><a href="maps.html">Maps</a></li>
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<li><a href="method-calls.html">Method Calls</a></li>
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<li><a href="control-flow.html">Control Flow</a></li>
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</ul>
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</td>
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<td>
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<ul>
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<li><a href="variables.html">Variables</a></li>
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<li><a href="functions.html">Functions</a></li>
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<li><a href="classes.html">Classes</a></li>
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<li><a href="concurrency.html">Concurrency</a></li>
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<li><a href="error-handling.html">Error Handling</a></li>
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<li><a href="modularity.html">Modularity</a></li>
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</ul>
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</td>
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<td>
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<ul>
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<li><a href="modules">Modules</a></li>
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<li><a href="embedding">Embedding</a></li>
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<li><a href="performance.html">Performance</a></li>
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<li><a href="qa.html">Q & A</a></li>
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</ul>
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</td>
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</tr>
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</table>
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</nav>
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<main>
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<h1>Values</h1>
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<p>Values are the built-in atomic object types that all other objects are composed
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of. They can be created through <em>literals</em>, expressions that evaluate to a
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value. All values are <em>immutable</em>—once created, they do not change. The
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number <code>3</code> is always the number <code>3</code>. The string <code>"frozen"</code> can never have its
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character array modified in place. </p>
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<h2>Booleans <a href="#booleans" name="booleans" class="header-anchor">#</a></h2>
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<p>A boolean value represents truth or falsehood. There are two boolean literals,
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<code>true</code> and <code>false</code>. Their class is <a href="modules/core/bool.html">Bool</a>. </p>
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<h2>Numbers <a href="#numbers" name="numbers" class="header-anchor">#</a></h2>
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<p>Like other scripting languages, Wren has a single numeric type:
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double-precision floating point. Number literals look like you expect coming
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from other languages: </p>
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<div class="codehilite"><pre><span></span><span class="mi">0</span>
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<span class="mi">1234</span>
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<span class="o">-</span><span class="mi">5678</span>
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<span class="mf">3.14159</span>
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<span class="mf">1.0</span>
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<span class="o">-</span><span class="mf">12.34</span>
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</pre></div>
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<p>Numbers are instances of the <a href="modules/core/num.html">Num</a> class. </p>
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<h2>Strings <a href="#strings" name="strings" class="header-anchor">#</a></h2>
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<p>A string is an array of bytes. Typically, they store characters encoded in
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UTF-8, but you can put any byte values in there, even zero or invalid UTF-8
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sequences. (You might have some trouble <em>printing</em> the latter to your terminal,
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though.) </p>
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<p>String literals are surrounded in double quotes: </p>
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<div class="codehilite"><pre><span></span><span class="s">"hi there"</span>
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</pre></div>
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<p>A handful of escape characters are supported: </p>
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<div class="codehilite"><pre><span></span><span class="s">"</span><span class="se">\0</span><span class="s">"</span> <span class="c1">// The NUL byte: 0.</span>
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<span class="s">"</span><span class="se">\"</span><span class="s">"</span> <span class="c1">// A double quote character.</span>
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<span class="s">"</span><span class="se">\\</span><span class="s">"</span> <span class="c1">// A backslash.</span>
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<span class="s">"</span><span class="se">\%</span><span class="s">"</span> <span class="c1">// A percent sign.</span>
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<span class="s">"</span><span class="se">\a</span><span class="s">"</span> <span class="c1">// Alarm beep. (Who uses this?)</span>
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<span class="s">"</span><span class="se">\b</span><span class="s">"</span> <span class="c1">// Backspace.</span>
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<span class="s">"</span><span class="se">\f</span><span class="s">"</span> <span class="c1">// Formfeed.</span>
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<span class="s">"</span><span class="se">\n</span><span class="s">"</span> <span class="c1">// Newline.</span>
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<span class="s">"</span><span class="se">\r</span><span class="s">"</span> <span class="c1">// Carriage return.</span>
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<span class="s">"</span><span class="se">\t</span><span class="s">"</span> <span class="c1">// Tab.</span>
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<span class="s">"</span><span class="se">\v</span><span class="s">"</span> <span class="c1">// Vertical tab.</span>
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</pre></div>
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<p>A <code>\u</code> followed by four hex digits can be used to specify a Unicode code point: </p>
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<div class="codehilite"><pre><span></span><span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="s">"</span><span class="se">\u0041\u0b83\u00DE</span><span class="s">"</span><span class="p">)</span> <span class="output">AஃÞ</span>
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</pre></div>
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<p>A capital <code>\U</code> followed by <em>eight</em> hex digits allows Unicode code points outside
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of the basic multilingual plane, like all-important emoji: </p>
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<div class="codehilite"><pre><span></span><span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="s">"</span><span class="se">\U0001F64A\U0001F680</span><span class="s">"</span><span class="p">)</span> <span class="output">🙊🚀</span>
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</pre></div>
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<p>A <code>\x</code> followed by two hex digits specifies a single unencoded byte: </p>
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<div class="codehilite"><pre><span></span><span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="s">"</span><span class="se">\x48\x69\x2e</span><span class="s">"</span><span class="p">)</span> <span class="output">Hi.</span>
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</pre></div>
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<p>Strings are instances of class <a href="modules/core/string.html">String</a>. </p>
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<h3>Interpolation <a href="#interpolation" name="interpolation" class="header-anchor">#</a></h3>
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<p>String literals also allow <em>interpolation</em>. If you have a percent sign (<code>%</code>)
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followed by a parenthesized expression, the expression is evaluated. The
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resulting object’s <code>toString</code> method is called and the result is inserted in the
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string: </p>
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<div class="codehilite"><pre><span></span><span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="s">"Math </span><span class="si">%(</span><span class="mi">3</span> <span class="o">+</span> <span class="mi">4</span> <span class="o">*</span> <span class="mi">5</span><span class="si">)</span><span class="s"> is fun!"</span><span class="p">)</span> <span class="output">Math 23 is fun!</span>
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</pre></div>
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<p>Arbitrarily complex expressions are allowed inside the parentheses: </p>
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<div class="codehilite"><pre><span></span><span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="s">"wow </span><span class="si">%(</span><span class="p">(</span><span class="mi">1</span><span class="o">..</span><span class="mi">3</span><span class="p">)</span><span class="o">.</span><span class="n">map</span> <span class="p">{</span><span class="o">|</span><span class="err">n</span><span class="o">|</span> <span class="err">n</span> <span class="o">*</span> <span class="err">n</span><span class="p">}</span><span class="o">.</span><span class="n">join</span><span class="p">()</span><span class="si">)</span><span class="s">"</span><span class="p">)</span> <span class="output">wow 149</span>
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</pre></div>
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<p>An interpolated expression can even contain a string literal which in turn has
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its own nested interpolations, but doing that gets unreadable pretty quickly. </p>
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<h2>Ranges <a href="#ranges" name="ranges" class="header-anchor">#</a></h2>
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<p>A range is a little object that represents a consecutive range of numbers. They
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don’t have their own dedicated literal syntax. Instead, the number class
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implements the <code>..</code> and <code>...</code> <a href="method-calls.html#operators">operators</a> to create them: </p>
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<div class="codehilite"><pre><span></span><span class="mi">3</span><span class="o">..</span><span class="mi">8</span>
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</pre></div>
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<p>This creates a range from three to eight, including eight itself. If you want a
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half-inclusive range, use <code>...</code>: </p>
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<div class="codehilite"><pre><span></span><span class="mi">4</span><span class="o">...</span><span class="mi">6</span>
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</pre></div>
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<p>This creates a range from four to six <em>not</em> including six itself. Ranges are
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commonly used for <a href="control-flow.html#for-statements">iterating</a> over a
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sequences of numbers, but are useful in other places too. You can pass them to
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a <a href="lists.html">list</a>‘s subscript operator to return a subset of the list, for
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example: </p>
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<div class="codehilite"><pre><span></span><span class="k">var</span> <span class="n">list</span> <span class="o">=</span> <span class="p">[</span><span class="s">"a"</span><span class="p">,</span> <span class="s">"b"</span><span class="p">,</span> <span class="s">"c"</span><span class="p">,</span> <span class="s">"d"</span><span class="p">,</span> <span class="s">"e"</span><span class="p">]</span>
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<span class="k">var</span> <span class="n">slice</span> <span class="o">=</span> <span class="n">list</span><span class="p">[</span><span class="mi">1</span><span class="o">..</span><span class="mi">3</span><span class="p">]</span>
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<span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="n">slice</span><span class="p">)</span> <span class="output">[b, c, d]</span>
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</pre></div>
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<p>Their class is <a href="modules/core/range.html">Range</a>. </p>
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<h2>Null <a href="#null" name="null" class="header-anchor">#</a></h2>
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<p>Wren has a special value <code>null</code>, which is the only instance of the class
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<a href="modules/core/null.html">Null</a>. (Note the difference in case.) It functions a bit like <code>void</code> in some
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languages: it indicates the absence of a value. If you call a method that
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doesn’t return anything and get its returned value, you get <code>null</code> back. </p>
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<p><a class="right" href="lists.html">Lists →</a>
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<a href="syntax.html">← Syntax</a> </p>
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</main>
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<footer>
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<div class="main-column">
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<p>Wren lives
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<a href="https://github.com/munificent/wren">on GitHub</a>
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— Made with ❤ by
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<a href="http://journal.stuffwithstuff.com/">Bob Nystrom</a> and
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<a href="https://github.com/munificent/wren/blob/master/AUTHORS">friends</a>.
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</p>
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