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<p class='location'>Module synom</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li><li><a href="#traits">Traits</a></li><li><a href="#types">Type Definitions</a></li></ul></div><p class='location'><a href='../index.html'>syn</a></p><script>window.sidebarCurrent = {name: 'synom', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script></div>
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<section id='main' class="content"><h1 class='fqn'><span class='in-band'>Module <a href='../index.html'>syn</a>::<wbr><a class="mod" href=''>synom</a></span><span class='out-of-band'><span id='render-detail'>
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<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
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[<span class='inner'>−</span>]
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</a>
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</span><a class='srclink' href='../../src/syn/synom.rs.html#9-415' title='goto source code'>[src]</a></span></h1><div class='docblock'><p>Parsing interface for parsing a token stream into a syntax tree node.</p>
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<p>Parsing in Syn is built on parser functions that take in a <a href="../buffer/index.html"><code>Cursor</code></a> and
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produce a <a href="type.PResult.html"><code>PResult<T></code></a> where <code>T</code> is some syntax tree node. <code>Cursor</code> is a
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cheaply copyable cursor over a range of tokens in a token stream, and
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<code>PResult</code> is a result that packages together a parsed syntax tree node <code>T</code>
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with a stream of remaining unparsed tokens after <code>T</code> represented as another
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<code>Cursor</code>, or a <a href="struct.ParseError.html"><code>ParseError</code></a> if parsing failed.</p>
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<p>This <code>Cursor</code>- and <code>PResult</code>-based interface is convenient for parser
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combinators and parser implementations, but not necessarily when you just
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have some tokens that you want to parse. For that we expose the following
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two entry points.</p>
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<h2 id="the-synparse-functions" class="section-header"><a href="#the-synparse-functions">The <code>syn::parse*</code> functions</a></h2>
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<p>The <a href="../fn.parse.html"><code>syn::parse</code></a>, <a href="../fn.parse2.html"><code>syn::parse2</code></a>, and <a href="../fn.parse_str.html"><code>syn::parse_str</code></a> functions serve
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as an entry point for parsing syntax tree nodes that can be parsed in an
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obvious default way. These functions can return any syntax tree node that
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implements the <a href="trait.Synom.html"><code>Synom</code></a> trait, which includes most types in Syn.</p>
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<pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">Type</span>;
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<span class="kw">let</span> <span class="ident">t</span>: <span class="ident">Type</span> <span class="op">=</span> <span class="ident">syn</span>::<span class="ident">parse_str</span>(<span class="string">"std::collections::HashMap<String, Value>"</span>)<span class="question-mark">?</span>;</pre>
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<p>The <a href="../macro.parse_quote.html"><code>parse_quote!</code></a> macro also uses this approach.</p>
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<h2 id="the-parser-trait" class="section-header"><a href="#the-parser-trait">The <code>Parser</code> trait</a></h2>
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<p>Some types can be parsed in several ways depending on context. For example
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an <a href="../struct.Attribute.html"><code>Attribute</code></a> can be either "outer" like <code>#[...]</code> or "inner" like
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<code>#![...]</code> and parsing the wrong one would be a bug. Similarly <a href="../punctuated/index.html"><code>Punctuated</code></a>
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may or may not allow trailing punctuation, and parsing it the wrong way
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would either reject valid input or accept invalid input.</p>
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<p>The <code>Synom</code> trait is not implemented in these cases because there is no good
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behavior to consider the default.</p>
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<div class='information'><div class='tooltip ignore'>ⓘ<span class='tooltiptext'>This example is not tested</span></div></div><pre class="rust rust-example-rendered ignore">
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<span class="comment">// Can't parse `Punctuated` without knowing whether trailing punctuation</span>
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<span class="comment">// should be allowed in this context.</span>
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<span class="kw">let</span> <span class="ident">path</span>: <span class="ident">Punctuated</span><span class="op"><</span><span class="ident">PathSegment</span>, <span class="macro">Token</span><span class="macro">!</span>[::]<span class="op">></span> <span class="op">=</span> <span class="ident">syn</span>::<span class="ident">parse</span>(<span class="ident">tokens</span>)<span class="question-mark">?</span>;</pre>
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<p>In these cases the types provide a choice of parser functions rather than a
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single <code>Synom</code> implementation, and those parser functions can be invoked
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through the <a href="trait.Parser.html"><code>Parser</code></a> trait.</p>
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<pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">synom</span>::<span class="ident">Parser</span>;
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<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">punctuated</span>::<span class="ident">Punctuated</span>;
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<span class="kw">use</span> <span class="ident">syn</span>::{<span class="ident">PathSegment</span>, <span class="ident">Expr</span>, <span class="ident">Attribute</span>};
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<span class="comment">// Parse a nonempty sequence of path segments separated by `::` punctuation</span>
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<span class="comment">// with no trailing punctuation.</span>
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<span class="kw">let</span> <span class="ident">parser</span> <span class="op">=</span> <span class="ident">Punctuated</span>::<span class="op"><</span><span class="ident">PathSegment</span>, <span class="macro">Token</span><span class="macro">!</span>[::]<span class="op">></span>::<span class="ident">parse_separated_nonempty</span>;
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<span class="kw">let</span> <span class="ident">path</span> <span class="op">=</span> <span class="ident">parser</span>.<span class="ident">parse</span>(<span class="ident">tokens</span>)<span class="question-mark">?</span>;
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<span class="comment">// Parse a possibly empty sequence of expressions terminated by commas with</span>
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<span class="comment">// an optional trailing punctuation.</span>
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<span class="kw">let</span> <span class="ident">parser</span> <span class="op">=</span> <span class="ident">Punctuated</span>::<span class="op"><</span><span class="ident">Expr</span>, <span class="macro">Token</span><span class="macro">!</span>[,]<span class="op">></span>::<span class="ident">parse_terminated</span>;
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<span class="kw">let</span> <span class="ident">args</span> <span class="op">=</span> <span class="ident">parser</span>.<span class="ident">parse</span>(<span class="ident">tokens</span>)<span class="question-mark">?</span>;
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<span class="comment">// Parse zero or more outer attributes but not inner attributes.</span>
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<span class="macro">named</span><span class="macro">!</span>(<span class="ident">outer_attrs</span> <span class="op">-></span> <span class="ident">Vec</span><span class="op"><</span><span class="ident">Attribute</span><span class="op">></span>, <span class="macro">many0</span><span class="macro">!</span>(<span class="ident">Attribute</span>::<span class="ident">parse_outer</span>));
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<span class="kw">let</span> <span class="ident">attrs</span> <span class="op">=</span> <span class="ident">outer_attrs</span>.<span class="ident">parse</span>(<span class="ident">tokens</span>)<span class="question-mark">?</span>;</pre>
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<h1 id="implementing-a-parser-function" class="section-header"><a href="#implementing-a-parser-function">Implementing a parser function</a></h1>
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<p>Parser functions are usually implemented using the <a href="https://github.com/Geal/nom"><code>nom</code></a>-style parser
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combinator macros provided by Syn, but may also be implemented without
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macros be using the low-level <a href="../buffer/index.html"><code>Cursor</code></a> API directly.</p>
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<p>The following parser combinator macros are available and a <code>Synom</code> parsing
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example is provided for each one.</p>
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<ul>
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<li><a href="../macro.alt.html"><code>alt!</code></a></li>
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<li><a href="../macro.braces.html"><code>braces!</code></a></li>
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<li><a href="../macro.brackets.html"><code>brackets!</code></a></li>
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<li><a href="../macro.call.html"><code>call!</code></a></li>
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<li><a href="../macro.cond.html"><code>cond!</code></a></li>
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<li><a href="../macro.cond_reduce.html"><code>cond_reduce!</code></a></li>
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<li><a href="../macro.custom_keyword.html"><code>custom_keyword!</code></a></li>
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<li><a href="../macro.do_parse.html"><code>do_parse!</code></a></li>
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<li><a href="../macro.epsilon.html"><code>epsilon!</code></a></li>
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<li><a href="../macro.input_end.html"><code>input_end!</code></a></li>
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<li><a href="../macro.keyword.html"><code>keyword!</code></a></li>
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<li><a href="../macro.many0.html"><code>many0!</code></a></li>
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<li><a href="../macro.map.html"><code>map!</code></a></li>
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<li><a href="../macro.not.html"><code>not!</code></a></li>
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<li><a href="../macro.option.html"><code>option!</code></a></li>
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<li><a href="../macro.parens.html"><code>parens!</code></a></li>
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<li><a href="../macro.punct.html"><code>punct!</code></a></li>
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<li><a href="../macro.reject.html"><code>reject!</code></a></li>
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<li><a href="../macro.switch.html"><code>switch!</code></a></li>
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<li><a href="../macro.syn.html"><code>syn!</code></a></li>
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<li><a href="../macro.tuple.html"><code>tuple!</code></a></li>
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<li><a href="../macro.value.html"><code>value!</code></a></li>
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</ul>
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<p><em>This module is available if Syn is built with the <code>"parsing"</code> feature.</em></p>
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</div><h2 id='modules' class='section-header'><a href="#modules">Modules</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="mod" href="ext/index.html"
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title='mod syn::synom::ext'>ext</a></td>
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<td class='docblock-short'>
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<p>Extension traits that are made available within the <code>call!</code> parser.</p>
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</td>
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</tr></table><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.ParseError.html"
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title='struct syn::synom::ParseError'>ParseError</a></td>
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<td class='docblock-short'>
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<p>Error returned when a <code>Synom</code> parser cannot parse the input tokens.</p>
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</td>
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</tr></table><h2 id='traits' class='section-header'><a href="#traits">Traits</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="trait" href="trait.Parser.html"
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title='trait syn::synom::Parser'>Parser</a></td>
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<td class='docblock-short'>
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<p>Parser that can parse Rust tokens into a particular syntax tree node.</p>
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</td>
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</tr>
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<tr class=' module-item'>
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<td><a class="trait" href="trait.Synom.html"
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title='trait syn::synom::Synom'>Synom</a></td>
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<td class='docblock-short'>
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<p>Parsing interface implemented by all types that can be parsed in a default
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way from a token stream.</p>
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</td>
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</tr></table><h2 id='types' class='section-header'><a href="#types">Type Definitions</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="type" href="type.PResult.html"
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title='type syn::synom::PResult'>PResult</a></td>
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<td class='docblock-short'>
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<p>The result of a <code>Synom</code> parser.</p>
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</td>
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</tr></table></section>
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<h1 class="hidden">Help</h1>
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</html>
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