<!DOCTYPE html><htmllang="en"><head><metacharset="utf-8"><metaname="viewport"content="width=device-width, initial-scale=1.0"><metaname="generator"content="rustdoc"><metaname="description"content="Parsing interface for parsing a token stream into a syntax tree node."><title>syn::parse - Rust</title><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><linkrel="stylesheet"href="../../static.files/normalize-76eba96aa4d2e634.css"><linkrel="stylesheet"href="../../static.files/rustdoc-5bc39a1768837dd0.css"><metaname="rustdoc-vars"data-root-path="../../"data-static-root-path="../../static.files/"data-current-crate="syn"data-themes=""data-resource-suffix=""data-rustdoc-version="1.77.0 (aedd173a2 2024-03-17)"data-channel="1.77.0"data-search-js="search-dd67cee4cfa65049.js"data-settings-js="settings-4313503d2e1961c2.js"><scriptsrc="../../static.files/storage-4c98445ec4002617.js"></script><scriptdefersrc="../sidebar-items.js"></script><scriptdefersrc="../../static.files/main-48f368f3872407c8.js"></script><noscript><linkrel="stylesheet"href="../../static.files/noscript-04d5337699b92874.css"></noscript><linkrel="alternate icon"type="image/png"href="../../static.files/favicon-16x16-8b506e7a72182f1c.png"><linkrel="alternate icon"type="image/png"href="../../static.files/favicon-32x32-422f7d1d52889060.png"><linkrel="icon"type="image/svg+xml"href="../../static.files/favicon-2c020d218678b618.svg"></head><bodyclass="rustdoc mod"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><navclass="mobile-topbar"><buttonclass="sidebar-menu-toggle"title="show sidebar"></button></nav><navclass="sidebar"><divclass="sidebar-crate"><h2><ahref="../../syn/index.html">syn</a><spanclass="version">2.0.52</span></h2></div><h2class="location"><ahref="#">Module parse</a></h2><divclass="sidebar-elems"><section><ulclass="block"><li><ahref="#modules">Modules</a></li><li><ahref="#structs">Structs</a></li><li><ahref="#traits">Traits</a></li><li><ahref="#types">Type Aliases</a></li></ul></section><h2><ahref="../index.html">In crate syn</a></h2></div></nav><divclass="sidebar-resizer"></div>
<main><divclass="width-limiter"><navclass="sub"><formclass="search-form"><span></span><divid="sidebar-button"tabindex="-1"><ahref="../../syn/all.html"title="show sidebar"></a></div><inputclass="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"><divid="help-button"tabindex="-1"><ahref="../../help.html"title="help">?</a></div><divid="settings-menu"tabindex="-1"><ahref="../../settings.html"title="settings"><imgwidth="22"height="22"alt="Change settings"src="../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><sectionid="main-content"class="content"><divclass="main-heading"><h1>Module <ahref="../index.html">syn</a>::<wbr><aclass="mod"href="#">parse</a><buttonid="copy-path"title="Copy item path to clipboard"><imgsrc="../../static.files/clipboard-7571035ce49a181d.svg"width="19"height="18"alt="Copy item path"></button></h1><spanclass="out-of-band"><aclass="src"href="../../src/syn/parse.rs.html#1-1381">source</a> · <buttonid="toggle-all-docs"title="collapse all docs">[<span>−</span>]</button></span></div><detailsclass="toggle top-doc"open><summaryclass="hideme"><span>Expand description</span></summary><divclass="docblock"><p>Parsing interface for parsing a token stream into a syntax tree node.</p>
<p>Parsing in Syn is built on parser functions that take in a <ahref="type.ParseStream.html"title="type syn::parse::ParseStream"><code>ParseStream</code></a>
and produce a <ahref="type.Result.html"title="type syn::parse::Result"><code>Result<T></code></a> where <code>T</code> is some syntax tree node. Underlying
these parser functions is a lower level mechanism built around the
<ahref="../buffer/struct.Cursor.html"title="struct syn::buffer::Cursor"><code>Cursor</code></a> type. <code>Cursor</code> is a cheaply copyable cursor over a range of
<p>Here is a snippet of parsing code to get a feel for the style of the
library. We define data structures for a subset of Rust syntax including
enums (not shown) and structs, then provide implementations of the <ahref="trait.Parse.html"title="trait syn::parse::Parse"><code>Parse</code></a>
trait to parse these syntax tree data structures from a token stream.</p>
<p>Once <code>Parse</code> impls have been defined, they can be called conveniently from a
procedural macro through <ahref="../macro.parse_macro_input.html"title="macro syn::parse_macro_input"><code>parse_macro_input!</code></a> as shown at the bottom of
the snippet. If the caller provides syntactically invalid input to the
procedural macro, they will receive a helpful compiler error message
pointing out the exact token that triggered the failure to parse.</p>
<p>Some types can be parsed in several ways depending on context. For example
an <ahref="../struct.Attribute.html"title="struct syn::Attribute"><code>Attribute</code></a> can be either “outer” like <code>#[...]</code> or “inner” like
<code>#![...]</code> and parsing the wrong one would be a bug. Similarly <ahref="../punctuated/index.html"title="mod syn::punctuated"><code>Punctuated</code></a>
may or may not allow trailing punctuation, and parsing it the wrong way
would either reject valid input or accept invalid input.</p>
<p>The <code>Parse</code> trait is not implemented in these cases because there is no good
behavior to consider the default.</p>
<divclass="example-wrap compile_fail"><ahref="#"class="tooltip"title="This example deliberately fails to compile">ⓘ</a><preclass="rust rust-example-rendered"><code><spanclass="comment">// Can't parse `Punctuated` without knowing whether trailing punctuation
</div></details><h2id="modules"class="section-header">Modules<ahref="#modules"class="anchor">§</a></h2><ulclass="item-table"><li><divclass="item-name"><aclass="mod"href="discouraged/index.html"title="mod syn::parse::discouraged">discouraged</a></div><divclass="desc docblock-short">Extensions to the parsing API with niche applicability.</div></li></ul><h2id="structs"class="section-header">Structs<ahref="#structs"class="anchor">§</a></h2><ulclass="item-table"><li><divclass="item-name"><aclass="struct"href="struct.Error.html"title="struct syn::parse::Error">Error</a></div><divclass="desc docblock-short">Error returned when a Syn parser cannot parse the input tokens.</div></li><li><divclass="item-name"><aclass="struct"href="struct.Lookahead1.html"title="struct syn::parse::Lookahead1">Lookahead1</a></div><divclass="desc docblock-short">Support for checking the next token in a stream to decide how to parse.</div></li><li><divclass="item-name"><aclass="struct"href="struct.Nothing.html"title="struct syn::parse::Nothing">Nothing</a></div><divclass="desc docblock-short">An empty syntax tree node that consumes no tokens when parsed.</div></li><li><divclass="item-name"><aclass="struct"href="struct.ParseBuffer.html"title="struct syn::parse::ParseBuffer">ParseBuffer</a></div><divclass="desc docblock-short">Cursor position within a buffered token stream.</div></li><li><divclass="item-name"><aclass="struct"href="struct.StepCursor.html"title="struct syn::parse::StepCursor">StepCursor</a></div><divclass="desc docblock-short">Cursor state associated with speculative parsing.</div></li></ul><h2id="traits"class="section-header">Traits<ahref="#traits"class="anchor">§</a></h2><ulclass="item-table"><li><divclass="item-name"><aclass="trait"href="trait.Parse.html"title="trait syn::parse::Parse">Parse</a></div><divclass="desc docblock-short">Parsing interface implemented by all types that can be parsed in a default
way from a token stream.</div></li><li><divclass="item-name"><aclass="trait"href="trait.Parser.html"title="trait syn::parse::Parser">Parser</a></div><divclass="desc docblock-short">Parser that can parse Rust tokens into a particular syntax tree node.</div></li><li><divclass="item-name"><aclass="trait"href="trait.Peek.html"title="trait syn::parse::Peek">Peek</a></div><divclass="desc docblock-short">Types that can be parsed by looking at just one token.</div></li></ul><h2id="types"class="section-header">Type Aliases<ahref="#types"class="anchor">§</a></h2><ulclass="item-table"><li><divclass="item-name"><aclass="type"href="type.ParseStream.html"title="type syn::parse::ParseStream">ParseStream</a></div><divclass="desc docblock-short">Input to a Syn parser function.</div></li><li><divclass="item-name"><aclass="type"href="type.Result.html"title="type syn::parse::Result">Result</a></div><divclass="desc docblock-short">The result of a Syn parser.</div></li></ul></section></div></main></body></html>
