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197 lines
6.9 KiB
HTML
197 lines
6.9 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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<script type="application/javascript" src="prism.js" data-manual></script>
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<script type="application/javascript" src="codejar.js"></script>
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<script type="application/javascript" src="wren.js"></script>
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<link rel="stylesheet" type="text/css" href="prism.css" />
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<link rel="stylesheet" type="text/css" href="style.css" />
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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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the viewport. -->
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<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1"/>
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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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<li><a href="try">Try it!</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>API docs</h2>
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<ul>
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<li><a href="modules">Modules</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="cli">Wren CLI</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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</section>
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</nav>
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<nav class="small">
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<table>
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<tr>
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<div><a href="getting-started.html">Getting Started</a></div>
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<div><a href="contributing.html">Contributing</a></div>
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<div><a href="blog">Blog</a></div>
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<div><a href="try">Try it!</a></div>
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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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</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">API/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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<pre class="snippet">
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var a = 1 + 2
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</pre>
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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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<pre class="snippet">
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var animal = "Slow Loris"
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System.print(animal) //> Slow Loris
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</pre>
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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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<pre class="snippet">
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{
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System.print(a) //! "a" doesn't exist yet.
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var a = 123
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System.print(a) //> 123
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}
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System.print(a) //! "a" doesn't exist anymore.
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</pre>
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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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<pre class="snippet">
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var a = "outer"
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{
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var a = "inner"
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System.print(a) //> inner
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}
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System.print(a) //> outer
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</pre>
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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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<pre class="snippet">
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var a = "hi"
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var a = "again" //! "a" is already declared.
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</pre>
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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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<pre class="snippet">
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var a = 123
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a = 234
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</pre>
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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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<pre class="snippet">
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var a = "before"
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System.print(a = "after") //> after
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</pre>
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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/main/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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</footer>
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</body>
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</html>
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