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184 lines
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HTML
184 lines
8.9 KiB
HTML
<!DOCTYPE html>
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<html>
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<head>
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<meta http-equiv="Content-type" content="text/html;charset=UTF-8" />
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<title>Variables – Wren</title>
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<link href='//fonts.googleapis.com/css?family=Source+Sans+Pro:400,700,400italic,700italic|Source+Code+Pro:400|Lato:400|Sanchez:400italic,400' rel='stylesheet' type='text/css'>
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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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<a href="./"><img src="./wren.svg" class="logo"></a>
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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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<li><a href="blog">Blog</a></li>
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</ul>
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<section>
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<h2>guides</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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<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>guides</h2></td>
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<td><h2>reference</h2></td>
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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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<h2>Variables</h2>
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<p>Variables are named slots for storing values. You define a new variable in Wren
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using a <code>var</code> statement, like so: </p>
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<div class="codehilite"><pre><span class="k">var</span> <span class="err">a</span> <span class="o">=</span> <span class="mi">1</span> <span class="o">+</span> <span class="mi">2</span>
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</pre></div>
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<p>This creates a new variable <code>a</code> in the current scope and initializes it with
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the result of the expression following the <code>=</code>. Once a variable has been
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defined, it can be accessed by name as you would expect. </p>
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<div class="codehilite"><pre><span class="k">var</span> <span class="n">animal</span> <span class="o">=</span> <span class="s">"Slow Loris"</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">animal</span><span class="p">)</span> <span class="output">Slow Loris</span>
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</pre></div>
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<h2>Scope <a href="#scope" name="scope" class="header-anchor">#</a></h2>
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<p>Wren has true block scope: a variable exists from the point where it is defined
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until the end of the <a href="syntax.html#blocks">block</a> where that definition appears. </p>
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<div class="codehilite"><pre><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="err">a</span><span class="p">)</span> <span class="error">"a" doesn't exist yet.</span>
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<span class="k">var</span> <span class="err">a</span> <span class="o">=</span> <span class="mi">123</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="err">a</span><span class="p">)</span> <span class="output">123</span>
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<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="err">a</span><span class="p">)</span> <span class="error">"a" doesn't exist anymore.</span>
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</pre></div>
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<p>Variables defined at the top level of a script are <em>top-level</em> and are visible
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to the <a href="modules.html">module</a> system. All other variables are <em>local</em>.
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Declaring a variable in an inner scope with the same name as an outer one is
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called <em>shadowing</em> and is not an error (although it’s not something you likely
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intend to do much). </p>
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<div class="codehilite"><pre><span class="k">var</span> <span class="err">a</span> <span class="o">=</span> <span class="s">"outer"</span>
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<span class="p">{</span>
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<span class="k">var</span> <span class="err">a</span> <span class="o">=</span> <span class="s">"inner"</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="err">a</span><span class="p">)</span> <span class="output">inner</span>
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<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="err">a</span><span class="p">)</span> <span class="output">outer</span>
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</pre></div>
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<p>Declaring a variable with the same name in the <em>same</em> scope <em>is</em> an error. </p>
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<div class="codehilite"><pre><span class="k">var</span> <span class="err">a</span> <span class="o">=</span> <span class="s">"hi"</span>
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<span class="k">var</span> <span class="err">a</span> <span class="o">=</span> <span class="s">"again"</span> <span class="error">"a" is already declared.</span>
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</pre></div>
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<h2>Assignment <a href="#assignment" name="assignment" class="header-anchor">#</a></h2>
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<p>After a variable has been declared, you can assign to it using <code>=</code>: </p>
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<div class="codehilite"><pre><span class="k">var</span> <span class="err">a</span> <span class="o">=</span> <span class="mi">123</span>
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<span class="err">a</span> <span class="o">=</span> <span class="mi">234</span>
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</pre></div>
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<p>An assignment walks up the scope stack to find where the named variable is
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declared. It’s an error to assign to a variable that isn’t defined. Wren
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doesn’t roll with implicit variable definition. </p>
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<p>When used in a larger expression, an assignment expression evaluates to the
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assigned value. </p>
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<div class="codehilite"><pre><span class="k">var</span> <span class="err">a</span> <span class="o">=</span> <span class="s">"before"</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="err">a</span> <span class="o">=</span> <span class="s">"after"</span><span class="p">)</span> <span class="output">after</span>
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</pre></div>
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<p>If the left-hand side is some more complex expression than a bare variable name,
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then it isn’t an assignment. Instead, it’s calling a <a href="method-calls.html#setters">setter method</a>. </p>
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<p><br><hr>
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<a class="right" href="functions.html">Functions →</a>
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<a href="control-flow.html">← Control Flow</a> </p>
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</main>
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</div>
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<footer>
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<div class="page">
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<div class="main-column">
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<p>Wren lives
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<a href="https://github.com/wren-lang/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/wren-lang/wren/blob/master/AUTHORS">friends</a>.
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</p>
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<div class="main-column">
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</div>
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