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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="API documentation for the Rust `cond` macro in crate `synom`."><meta name="keywords" content="rust, rustlang, rust-lang, cond"><title>synom::cond - Rust</title><link rel="stylesheet" type="text/css" href="../normalize.css"><link rel="stylesheet" type="text/css" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../dark.css"><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script src="../storage.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="shortcut icon" href="../favicon.ico"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc macro"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../synom/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><div class="sidebar-elems"><p class='location'><a href='index.html'>synom</a></p><script>window.sidebarCurrent = {name: 'cond', ty: 'macro', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../settings.html"><img src="../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../src/synom/lib.rs.html#307-322' title='goto source code'>[src]</a></span><span class='in-band'>Macro <a href='index.html'>synom</a>::<wbr><a class="macro" href=''>cond</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><div class="example-wrap"><pre class="rust macro">
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<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">cond</span> {
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">cond</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">submac</span>:<span class="macro">ident</span><span class="macro">!</span>( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">args</span>:<span class="ident">tt</span>)<span class="op">*</span> )) <span class="op">=</span><span class="op">></span> { ... };
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">cond</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>) <span class="op">=</span><span class="op">></span> { ... };
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}</pre></div>
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</div><div class='docblock'><p>Conditionally execute the given parser.</p>
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<p>If you are familiar with nom, this is nom's <code>cond_with_error</code> parser.</p>
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<ul>
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<li><strong>Syntax:</strong> <code>cond!(CONDITION, THING)</code></li>
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<li><strong>Output:</strong> <code>Some(THING)</code> if the condition is true, else <code>None</code></li>
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</ul>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">syn</span>;
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<span class="attribute">#[<span class="ident">macro_use</span>]</span> <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">synom</span>;
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<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">parse</span>::<span class="ident">boolean</span>;
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<span class="comment">// Parses a tuple of booleans like `(true, false, false)`, possibly with a</span>
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<span class="comment">// dotdot indicating omitted values like `(true, true, .., true)`. Returns</span>
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<span class="comment">// separate vectors for the booleans before and after the dotdot. The second</span>
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<span class="comment">// vector is None if there was no dotdot.</span>
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">bools_with_dotdot</span> <span class="op">-</span><span class="op">></span> (<span class="ident">Vec</span><span class="op"><</span><span class="ident">bool</span><span class="op">></span>, <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Vec</span><span class="op"><</span><span class="ident">bool</span><span class="op">></span><span class="op">></span>), <span class="macro">do_parse</span><span class="macro">!</span>(
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<span class="macro">punct</span><span class="macro">!</span>(<span class="string">"("</span>) <span class="op">></span><span class="op">></span>
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<span class="ident">before</span>: <span class="macro">separated_list</span><span class="macro">!</span>(<span class="macro">punct</span><span class="macro">!</span>(<span class="string">","</span>), <span class="ident">boolean</span>) <span class="op">></span><span class="op">></span>
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<span class="ident">after</span>: <span class="macro">option</span><span class="macro">!</span>(<span class="macro">do_parse</span><span class="macro">!</span>(
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<span class="comment">// Only allow comma if there are elements before dotdot, i.e. cannot</span>
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<span class="comment">// be `(, .., true)`.</span>
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<span class="macro">cond</span><span class="macro">!</span>(<span class="op">!</span><span class="ident">before</span>.<span class="ident">is_empty</span>(), <span class="macro">punct</span><span class="macro">!</span>(<span class="string">","</span>)) <span class="op">></span><span class="op">></span>
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<span class="macro">punct</span><span class="macro">!</span>(<span class="string">".."</span>) <span class="op">></span><span class="op">></span>
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<span class="ident">after</span>: <span class="macro">many0</span><span class="macro">!</span>(<span class="macro">preceded</span><span class="macro">!</span>(<span class="macro">punct</span><span class="macro">!</span>(<span class="string">","</span>), <span class="ident">boolean</span>)) <span class="op">></span><span class="op">></span>
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<span class="comment">// Only allow trailing comma if there are elements after dotdot,</span>
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<span class="comment">// i.e. cannot be `(true, .., )`.</span>
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<span class="macro">cond</span><span class="macro">!</span>(<span class="op">!</span><span class="ident">after</span>.<span class="ident">is_empty</span>(), <span class="macro">option</span><span class="macro">!</span>(<span class="macro">punct</span><span class="macro">!</span>(<span class="string">","</span>))) <span class="op">></span><span class="op">></span>
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(<span class="ident">after</span>)
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)) <span class="op">></span><span class="op">></span>
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<span class="comment">// Allow trailing comma if there is no dotdot but there are elements.</span>
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<span class="macro">cond</span><span class="macro">!</span>(<span class="op">!</span><span class="ident">before</span>.<span class="ident">is_empty</span>() <span class="kw-2">&</span><span class="op">&</span> <span class="ident">after</span>.<span class="ident">is_none</span>(), <span class="macro">option</span><span class="macro">!</span>(<span class="macro">punct</span><span class="macro">!</span>(<span class="string">","</span>))) <span class="op">></span><span class="op">></span>
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<span class="macro">punct</span><span class="macro">!</span>(<span class="string">")"</span>) <span class="op">></span><span class="op">></span>
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(<span class="ident">before</span>, <span class="ident">after</span>)
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));
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<span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="string">"(true, false, false)"</span>;
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<span class="kw">let</span> <span class="ident">parsed</span> <span class="op">=</span> <span class="ident">bools_with_dotdot</span>(<span class="ident">input</span>).<span class="ident">expect</span>(<span class="string">"bools with dotdot"</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">parsed</span>, (<span class="macro">vec</span><span class="macro">!</span>[<span class="bool-val">true</span>, <span class="bool-val">false</span>, <span class="bool-val">false</span>], <span class="prelude-val">None</span>));
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<span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="string">"(true, true, .., true)"</span>;
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<span class="kw">let</span> <span class="ident">parsed</span> <span class="op">=</span> <span class="ident">bools_with_dotdot</span>(<span class="ident">input</span>).<span class="ident">expect</span>(<span class="string">"bools with dotdot"</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">parsed</span>, (<span class="macro">vec</span><span class="macro">!</span>[<span class="bool-val">true</span>, <span class="bool-val">true</span>], <span class="prelude-val">Some</span>(<span class="macro">vec</span><span class="macro">!</span>[<span class="bool-val">true</span>])));
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<span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="string">"(.., true)"</span>;
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<span class="kw">let</span> <span class="ident">parsed</span> <span class="op">=</span> <span class="ident">bools_with_dotdot</span>(<span class="ident">input</span>).<span class="ident">expect</span>(<span class="string">"bools with dotdot"</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">parsed</span>, (<span class="macro">vec</span><span class="macro">!</span>[], <span class="prelude-val">Some</span>(<span class="macro">vec</span><span class="macro">!</span>[<span class="bool-val">true</span>])));
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<span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="string">"(true, true, ..)"</span>;
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<span class="kw">let</span> <span class="ident">parsed</span> <span class="op">=</span> <span class="ident">bools_with_dotdot</span>(<span class="ident">input</span>).<span class="ident">expect</span>(<span class="string">"bools with dotdot"</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">parsed</span>, (<span class="macro">vec</span><span class="macro">!</span>[<span class="bool-val">true</span>, <span class="bool-val">true</span>], <span class="prelude-val">Some</span>(<span class="macro">vec</span><span class="macro">!</span>[])));
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<span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="string">"(..)"</span>;
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<span class="kw">let</span> <span class="ident">parsed</span> <span class="op">=</span> <span class="ident">bools_with_dotdot</span>(<span class="ident">input</span>).<span class="ident">expect</span>(<span class="string">"bools with dotdot"</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">parsed</span>, (<span class="macro">vec</span><span class="macro">!</span>[], <span class="prelude-val">Some</span>(<span class="macro">vec</span><span class="macro">!</span>[])));
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}</pre></div>
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