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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="Tests a list of parsers one by one until one succeeds."><meta name="keywords" content="rust, rustlang, rust-lang, alt"><title>alt in nom::branch - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><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="../../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../../dark.css" disabled><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../favicon.svg"></head><body class="rustdoc fn"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../../nom/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2 class="location"></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../nom/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><div class="sidebar-elems"><h2 class="location"><a href="index.html">In nom::branch</a></h2></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../../nom/index.html"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></a><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><button type="button">?</button></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../wheel.svg"></a></div></div></form></nav></div><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn"><span class="in-band">Function <a href="../index.html">nom</a>::<wbr><a href="index.html">branch</a>::<wbr><a class="fn" href="#">alt</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></span></h1><span class="out-of-band"><a class="srclink" href="../../src/nom/branch/mod.rs.html#47-51">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="docblock item-decl"><pre class="rust fn"><code>pub fn alt<I: <a class="trait" href="https://doc.rust-lang.org/1.64.0/core/clone/trait.Clone.html" title="trait core::clone::Clone">Clone</a>, O, E: <a class="trait" href="../error/trait.ParseError.html" title="trait nom::error::ParseError">ParseError</a><I>, List: <a class="trait" href="trait.Alt.html" title="trait nom::branch::Alt">Alt</a><I, O, E>>(<br> l: List<br>) -> impl <a class="trait" href="https://doc.rust-lang.org/1.64.0/core/ops/function/trait.FnMut.html" title="trait core::ops::function::FnMut">FnMut</a>(I) -> <a class="type" href="../type.IResult.html" title="type nom::IResult">IResult</a><I, O, E></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Tests a list of parsers one by one until one succeeds.</p>
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<p>It takes as argument a tuple of parsers. There is a maximum of 21
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parsers. If you need more, it is possible to nest them in other <code>alt</code> calls,
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like this: <code>alt(parser_a, alt(parser_b, parser_c))</code></p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">nom::character::complete</span>::{<span class="ident">alpha1</span>, <span class="ident">digit1</span>};
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<span class="kw">use</span> <span class="ident">nom::branch::alt</span>;
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<span class="kw">fn</span> <span class="ident">parser</span>(<span class="ident">input</span>: <span class="kw-2">&</span><span class="ident">str</span>) -> <span class="ident">IResult</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">str</span>, <span class="kw-2">&</span><span class="ident">str</span><span class="op">></span> {
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<span class="ident">alt</span>((<span class="ident">alpha1</span>, <span class="ident">digit1</span>))(<span class="ident">input</span>)
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};
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<span class="comment">// the first parser, alpha1, recognizes the input</span>
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<span class="macro">assert_eq!</span>(<span class="ident">parser</span>(<span class="string">"abc"</span>), <span class="prelude-val">Ok</span>((<span class="string">""</span>, <span class="string">"abc"</span>)));
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<span class="comment">// the first parser returns an error, so alt tries the second one</span>
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<span class="macro">assert_eq!</span>(<span class="ident">parser</span>(<span class="string">"123456"</span>), <span class="prelude-val">Ok</span>((<span class="string">""</span>, <span class="string">"123456"</span>)));
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<span class="comment">// both parsers failed, and with the default error type, alt will return the last error</span>
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<span class="macro">assert_eq!</span>(<span class="ident">parser</span>(<span class="string">" "</span>), <span class="prelude-val">Err</span>(<span class="ident">Err::Error</span>(<span class="macro">error_position!</span>(<span class="string">" "</span>, <span class="ident">ErrorKind::Digit</span>))));</code></pre></div>
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<p>With a custom error type, it is possible to have alt return the error of the parser
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that went the farthest in the input data</p>
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