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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="Pick the first successful parser"><title>alt in winnow::combinator - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-ac92e1bbe349e143.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="winnow" data-themes="" data-resource-suffix="" data-rustdoc-version="1.76.0 (07dca489a 2024-02-04)" data-channel="1.76.0" data-search-js="search-2b6ce74ff89ae146.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../static.files/storage-f2adc0d6ca4d09fb.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../static.files/main-305769736d49e732.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-feafe1bb7466e4bd.css"></noscript><link rel="alternate icon" type="image/png" href="../../static.files/favicon-16x16-8b506e7a72182f1c.png"><link rel="alternate icon" type="image/png" href="../../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../../static.files/favicon-2c020d218678b618.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></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../winnow/index.html">winnow</a><span class="version">0.6.5</span></h2></div><div class="sidebar-elems"><h2><a href="index.html">In winnow::combinator</a></h2></div></nav><div class="sidebar-resizer"></div>
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<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../../winnow/all.html" title="show sidebar"></a></div><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" tabindex="-1"><a href="../../help.html" title="help">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Function <a href="../index.html">winnow</a>::<wbr><a href="index.html">combinator</a>::<wbr><a class="fn" href="#">alt</a><button id="copy-path" title="Copy item path to clipboard"><img src="../../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../../src/winnow/combinator/branch.rs.html#51-59">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><pre class="rust item-decl"><code>pub fn alt<Input: <a class="trait" href="../stream/trait.Stream.html" title="trait winnow::stream::Stream">Stream</a>, Output, Error, Alternatives>(
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alternatives: Alternatives
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) -> impl <a class="trait" href="../trait.Parser.html" title="trait winnow::Parser">Parser</a><Input, Output, Error><div class="where">where
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Alternatives: <a class="trait" href="trait.Alt.html" title="trait winnow::combinator::Alt">Alt</a><Input, Output, Error>,
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Error: <a class="trait" href="../error/trait.ParserError.html" title="trait winnow::error::ParserError">ParserError</a><Input>,</div></code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Pick the first successful parser</p>
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<p>To stop on an error, rather than trying further cases, see
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<a href="fn.cut_err.html" title="fn winnow::combinator::cut_err"><code>cut_err</code></a> ([example][crate::_tutorial::chapter_6]).</p>
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<p>For tight control over the error when no match is found, add a final case using <a href="fn.fail.html" title="fn winnow::combinator::fail"><code>fail</code></a>.
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Alternatively, with a [custom error type][crate::_topic::error], it is possible to track all
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errors or return the error of the parser that went the farthest in the input data.</p>
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<p>When the alternative cases have unique prefixes, <a href="macro.dispatch.html" title="macro winnow::combinator::dispatch"><code>dispatch</code></a> can offer better performance.</p>
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<h2 id="example"><a href="#example">Example</a></h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>winnow::ascii::{alpha1, digit1};
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<span class="kw">use </span>winnow::combinator::alt;
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<span class="kw">fn </span>parser(input: <span class="kw-2">&</span>str) -> IResult<<span class="kw-2">&</span>str, <span class="kw-2">&</span>str> {
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alt((alpha1, digit1)).parse_peek(input)
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};
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<span class="comment">// the first parser, alpha1, recognizes the input
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</span><span class="macro">assert_eq!</span>(parser(<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
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</span><span class="macro">assert_eq!</span>(parser(<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
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</span><span class="macro">assert_eq!</span>(parser(<span class="string">" "</span>), <span class="prelude-val">Err</span>(ErrMode::Backtrack(InputError::new(<span class="string">" "</span>, ErrorKind::Slice))));</code></pre></div>
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