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367 lines
16 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>Syntax – Wren</title>
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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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<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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<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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</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">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>Syntax</h2>
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<p>Wren’s syntax is designed to be familiar to people coming from C-like languages
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while being a bit simpler and more streamlined. </p>
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<p>Scripts are stored in plain text files with a <code>.wren</code> file extension. Wren does
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not compile ahead of time: programs are run directly from source, from top to
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bottom like a typical scripting language. (Internally, programs are compiled to
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bytecode for <a href="performance.html">efficiency</a>, but that’s an implementation detail.) </p>
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<h2>Comments <a href="#comments" name="comments" class="header-anchor">#</a></h2>
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<p>Line comments start with <code>//</code> and end at the end of the line:</p>
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<div class="codehilite"><pre><span class="c1">// This is a comment.</span>
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</pre></div>
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<p>Block comments start with <code>/*</code> and end with <code>*/</code>. They can span multiple lines: </p>
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<div class="codehilite"><pre><span class="cm">/* This </span>
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<span class="cm"> is </span>
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<span class="cm"> a </span>
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<span class="cm"> multi-line </span>
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<span class="cm"> comment. */</span>
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</pre></div>
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<p>Unlike C, block comments can nest in Wren: </p>
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<div class="codehilite"><pre><span class="cm">/* This is /* a nested */ comment. */</span>
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</pre></div>
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<p>This is handy because it lets you easily comment out an entire block of code,
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even if the code already contains block comments. </p>
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<h2>Reserved words <a href="#reserved-words" name="reserved-words" class="header-anchor">#</a></h2>
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<p>One way to get a quick feel for a language’s style is to see what words it
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reserves. Here’s what Wren has: </p>
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<div class="codehilite"><pre><span class="k">break</span> <span class="k">class</span> <span class="k">construct</span> <span class="k">else</span> <span class="kc">false</span> <span class="k">for</span> <span class="k">foreign</span> <span class="k">if</span> <span class="k">import</span>
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<span class="k">in</span> <span class="k">is</span> <span class="kc">null</span> <span class="k">return</span> <span class="k">static</span> <span class="k">super</span> <span class="nb">this</span> <span class="kc">true</span> <span class="k">var</span> <span class="k">while</span>
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</pre></div>
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<h2>Identifiers <a href="#identifiers" name="identifiers" class="header-anchor">#</a></h2>
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<p>Naming rules are similar to other programming languages. Identifiers start with
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a letter or underscore and may contain letters, digits, and underscores. Case
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is sensitive. </p>
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<div class="codehilite"><pre><span class="n">hi</span>
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<span class="n">camelCase</span>
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<span class="vg">PascalCase</span>
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<span class="vi">_under_score</span>
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<span class="n">abc123</span>
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<span class="vg">ALL_CAPS</span>
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</pre></div>
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<p>Identifiers that start with underscore (<code>_</code>) are special in Wren. They are used
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to indicate <a href="classes.html#fields">fields</a> in classes. </p>
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<h2>Newlines <a href="#newlines" name="newlines" class="header-anchor">#</a></h2>
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<p>Newlines (<code>\n</code>) are meaningful in Wren. They are used to separate statements: </p>
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<div class="codehilite"><pre><span class="c1">// Two statements:</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="s">"hi"</span><span class="p">)</span> <span class="c1">// Newline.</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="s">"bye"</span><span class="p">)</span>
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</pre></div>
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<p>Sometimes, though, a statement doesn’t fit on a single line and jamming a
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newline in the middle would trip it up. To handle that, Wren has a very simple
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rule: It ignores a newline following any token that can’t end a statement. </p>
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<div class="codehilite"><pre><span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span> <span class="c1">// Newline here is ignored.</span>
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<span class="s">"hi"</span><span class="p">)</span>
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</pre></div>
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<p>In practice, this means you can put each statement on its own line and wrap
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them across lines as needed without too much trouble. </p>
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<h2>Blocks <a href="#blocks" name="blocks" class="header-anchor">#</a></h2>
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<p>Wren uses curly braces to define <em>blocks</em>. You can use a block anywhere a
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statement is allowed, like in <a href="control-flow.html">control flow</a> statements.
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<a href="classes.html#methods">Method</a> and <a href="functions.html">function</a> bodies are also
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blocks. For example, here we have a block for the then case, and a single
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statement for the else: </p>
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<div class="codehilite"><pre><span class="k">if</span> <span class="p">(</span><span class="n">happy</span> <span class="o">&&</span> <span class="n">knowIt</span><span class="p">)</span> <span class="p">{</span>
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<span class="n">hands</span><span class="o">.</span><span class="n">clap</span><span class="p">()</span>
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<span class="p">}</span> <span class="k">else</span> <span class="vg">System</span><span class="o">.</span><span class="n">print</span><span class="p">(</span><span class="s">"sad"</span><span class="p">)</span>
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</pre></div>
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<p>Blocks have two similar but not identical forms. Typically, blocks contain a
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series of statements like: </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="s">"one"</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="s">"two"</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="s">"three"</span><span class="p">)</span>
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<span class="p">}</span>
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</pre></div>
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<p>Blocks of this form when used for method and function bodies automatically
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return <code>null</code> after the block has completed. If you want to return a different
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value, you need an explicit <code>return</code> statement. </p>
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<p>However, it’s pretty common to have a method or function that just evaluates and
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returns the result of a single expression. Some other languages use <code>=></code> to
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define these. Wren uses: </p>
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<div class="codehilite"><pre><span class="p">{</span> <span class="s">"single expression"</span> <span class="p">}</span>
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</pre></div>
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<p>If there is no newline after the <code>{</code> (or after the parameter list in a
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<a href="functions.html">function</a>), then the block may only contain a single
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expression, and it automatically returns the result of it. It’s exactly the same
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as doing: </p>
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<div class="codehilite"><pre><span class="p">{</span>
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<span class="k">return</span> <span class="s">"single expression"</span>
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<span class="p">}</span>
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</pre></div>
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<p>Statements are not allowed in this form (since they don’t produce values), which
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means nothing starting with <code>class</code>, <code>for</code>, <code>if</code>, <code>import</code>, <code>return</code>,
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<code>var</code>, or <code>while</code>. If you want a block that contains a single statement,
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put a newline in there: </p>
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<div class="codehilite"><pre><span class="p">{</span>
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<span class="k">if</span> <span class="p">(</span><span class="n">happy</span><span class="p">)</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="s">"I'm feelin' it!"</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</pre></div>
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<p>Using an initial newline after the <code>{</code> does feel a little weird or magical, but
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newlines are already significant in Wren, so it’s not totally crazy. The nice
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thing about this syntax as opposed to something like <code>=></code> is that the <em>end</em> of
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the block has an explicit delimiter. That helps when chaining: </p>
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<div class="codehilite"><pre><span class="n">numbers</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="mi">2</span> <span class="p">}</span><span class="o">.</span><span class="n">where</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="mi">100</span> <span class="p">}</span>
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</pre></div>
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<h2>Precedence and Associativity <a href="#precedence-and-associativity" name="precedence-and-associativity" class="header-anchor">#</a></h2>
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<p>We’ll talk about Wren’s different expression forms and what they mean in the
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next few pages. But if you want to see how they interact with each other
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grammatically, here’s the whole table. </p>
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<p>It shows which expressions have higher <em>precedence</em>—which ones bind more
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tightly than others—and their <em>associativity</em>—how a series of the
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same kind of expression is ordered. Wren mostly follows C, except that it fixes
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<a href="http://www.lysator.liu.se/c/dmr-on-or.html">the bitwise operator mistake</a>. The full precedence table, from
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tightest to loosest, is: </p>
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<table class="precedence">
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<tbody>
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<tr>
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<th>Prec</th>
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<th>Operator</th>
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<th>Description</th>
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<th>Associates</th>
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</tr>
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<tr>
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<td>1</td>
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<td><code>()</code> <code>[]</code> <code>.</code></td>
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<td>Grouping, <a href="method-calls.html">Subscript, Method call</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>2</td>
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<td><code>-</code> <code>!</code> <code>~</code></td>
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<td><a href="method-calls.html#operators">Negate, Not, Complement</a></td>
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<td>Right</td>
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</tr>
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<tr>
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<td>3</td>
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<td><code>*</code> <code>/</code> <code>%</code></td>
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<td><a href="method-calls.html#operators">Multiply, Divide, Modulo</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>4</td>
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<td><code>+</code> <code>-</code></td>
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<td><a href="method-calls.html#operators">Add, Subtract</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>5</td>
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<td><code>..</code> <code>...</code></td>
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<td><a href="method-calls.html#operators">Inclusive range, Exclusive range</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>6</td>
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<td><code><<</code> <code>>></code></td>
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<td><a href="method-calls.html#operators">Left shift, Right shift</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>7</td>
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<td><code>&</code></td>
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<td><a href="method-calls.html#operators">Bitwise and</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>8</td>
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<td><code>^</code></td>
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<td><a href="method-calls.html#operators">Bitwise xor</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>9</td>
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<td><code>|</code></td>
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<td><a href="method-calls.html#operators">Bitwise or</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>10</td>
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<td><code><</code> <code><=</code> <code>></code> <code>>=</code></td>
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<td><a href="method-calls.html#operators">Comparison</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>11</td>
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<td><code>is</code></td>
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<td><a href="method-calls.html#operators">Type test</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>12</td>
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<td><code>==</code> <code>!=</code></td>
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<td><a href="method-calls.html#operators">Equals, Not equal</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>13</td>
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<td><code>&&</code></td>
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<td><a href="control-flow.html#logical-operators">Logical and</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>14</td>
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<td><code>||</code></td>
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<td><a href="control-flow.html#logical-operators">Logical or</a></td>
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<td>Left</td>
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</tr>
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<tr>
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<td>15</td>
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<td><code>?:</code></td>
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<td><a href="control-flow.html#the-conditional-operator-">Conditional</a></td>
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<td>Right</td>
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</tr>
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<tr>
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<td>16</td>
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<td><code>=</code></td>
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<td><a href="variables.html#assignment">Assignment</a>, <a href="method-calls.html#setters">Setter</a></td>
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<td>Right</td>
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</tr>
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</tbody>
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</table>
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<p><br><hr>
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<a class="right" href="values.html">Values →</a>
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<a href="getting-started.html">← Getting Started</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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</footer>
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</body>
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</html>
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