239 lines
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239 lines
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<div class="sidebar-menu">☰</div>
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<p class='location'>Module buffer</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#structs">Structs</a></li></ul></div><p class='location'><a href='../index.html'>syn</a></p><script>window.sidebarCurrent = {name: 'buffer', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script></div>
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<section id='main' class="content">
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<h1 class='fqn'><span class='in-band'>Module <a href='../index.html'>syn</a>::<wbr><a class="mod" href=''>buffer</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/buffer.rs.html#9-469' title='goto source code'>[src]</a></span></h1>
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<div class='docblock'><p>A stably addressed token buffer supporting efficient traversal based on a
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cheaply copyable cursor.</p>
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<p>The <a href="../synom/trait.Synom.html"><code>Synom</code></a> trait is implemented for syntax tree types that can be parsed
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from one of these token cursors.</p>
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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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<h1 id="example" class="section-header"><a href="#example">Example</a></h1>
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<p>This example shows a basic token parser for parsing a token stream without
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using Syn's parser combinator macros.</p>
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<pre class="rust rust-example-rendered">
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<span class="attribute">#![<span class="ident">feature</span>(<span class="ident">proc_macro_diagnostic</span>)]</span>
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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="kw">extern</span> <span class="kw">crate</span> <span class="ident">proc_macro</span>;
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<span class="attribute">#[<span class="ident">macro_use</span>]</span>
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<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">quote</span>;
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<span class="kw">use</span> <span class="ident">syn</span>::{<span class="ident">token</span>, <span class="ident">ExprTuple</span>};
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<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">buffer</span>::{<span class="ident">Cursor</span>, <span class="ident">TokenBuffer</span>};
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<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">spanned</span>::<span class="ident">Spanned</span>;
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<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">synom</span>::<span class="ident">Synom</span>;
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<span class="kw">use</span> <span class="ident">proc_macro</span>::{<span class="ident">Diagnostic</span>, <span class="ident">Span</span>, <span class="ident">TokenStream</span>};
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<span class="doccomment">/// A basic token parser for parsing a token stream without using Syn's</span>
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<span class="doccomment">/// parser combinator macros.</span>
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<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Parser</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
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<span class="ident">cursor</span>: <span class="ident">Cursor</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>,
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}
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<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="ident">Parser</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
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<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">cursor</span>: <span class="ident">Cursor</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>) <span class="op">-></span> <span class="self">Self</span> {
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<span class="ident">Parser</span> { <span class="ident">cursor</span> }
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}
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<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">current_span</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Span</span> {
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<span class="self">self</span>.<span class="ident">cursor</span>.<span class="ident">span</span>().<span class="ident">unstable</span>()
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}
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<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">parse</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Synom</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">Diagnostic</span><span class="op">></span> {
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<span class="kw">let</span> (<span class="ident">val</span>, <span class="ident">rest</span>) <span class="op">=</span> <span class="ident">T</span>::<span class="ident">parse</span>(<span class="self">self</span>.<span class="ident">cursor</span>)
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.<span class="ident">map_err</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="kw">match</span> <span class="ident">T</span>::<span class="ident">description</span>() {
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<span class="prelude-val">Some</span>(<span class="ident">desc</span>) <span class="op">=></span> {
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<span class="self">self</span>.<span class="ident">current_span</span>().<span class="ident">error</span>(<span class="macro">format</span><span class="macro">!</span>(<span class="string">"{}: expected {}"</span>, <span class="ident">e</span>, <span class="ident">desc</span>))
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}
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<span class="prelude-val">None</span> <span class="op">=></span> {
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<span class="self">self</span>.<span class="ident">current_span</span>().<span class="ident">error</span>(<span class="ident">e</span>.<span class="ident">to_string</span>())
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}
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})<span class="question-mark">?</span>;
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<span class="self">self</span>.<span class="ident">cursor</span> <span class="op">=</span> <span class="ident">rest</span>;
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<span class="prelude-val">Ok</span>(<span class="ident">val</span>)
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}
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<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">expect_eof</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Diagnostic</span><span class="op">></span> {
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<span class="kw">if</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">cursor</span>.<span class="ident">eof</span>() {
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<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="self">self</span>.<span class="ident">current_span</span>().<span class="ident">error</span>(<span class="string">"trailing characters; expected eof"</span>));
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}
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<span class="prelude-val">Ok</span>(())
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}
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}
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<span class="kw">fn</span> <span class="ident">eval</span>(<span class="ident">input</span>: <span class="ident">TokenStream</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">TokenStream</span>, <span class="ident">Diagnostic</span><span class="op">></span> {
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<span class="kw">let</span> <span class="ident">buffer</span> <span class="op">=</span> <span class="ident">TokenBuffer</span>::<span class="ident">new</span>(<span class="ident">input</span>);
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">parser</span> <span class="op">=</span> <span class="ident">Parser</span>::<span class="ident">new</span>(<span class="ident">buffer</span>.<span class="ident">begin</span>());
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<span class="comment">// Parse some syntax tree types out of the input tokens. In this case we</span>
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<span class="comment">// expect something like:</span>
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<span class="comment">//</span>
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<span class="comment">// (a, b, c) = (1, 2, 3)</span>
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<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="ident">parser</span>.<span class="ident">parse</span>::<span class="op"><</span><span class="ident">ExprTuple</span><span class="op">></span>()<span class="question-mark">?</span>;
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<span class="ident">parser</span>.<span class="ident">parse</span>::<span class="op"><</span><span class="ident">token</span>::<span class="ident">Eq</span><span class="op">></span>()<span class="question-mark">?</span>;
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<span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="ident">parser</span>.<span class="ident">parse</span>::<span class="op"><</span><span class="ident">ExprTuple</span><span class="op">></span>()<span class="question-mark">?</span>;
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<span class="ident">parser</span>.<span class="ident">expect_eof</span>()<span class="question-mark">?</span>;
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<span class="comment">// Perform some validation and report errors.</span>
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<span class="kw">let</span> (<span class="ident">a_len</span>, <span class="ident">b_len</span>) <span class="op">=</span> (<span class="ident">a</span>.<span class="ident">elems</span>.<span class="ident">len</span>(), <span class="ident">b</span>.<span class="ident">elems</span>.<span class="ident">len</span>());
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<span class="kw">if</span> <span class="ident">a_len</span> <span class="op">!=</span> <span class="ident">b_len</span> {
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<span class="kw">let</span> <span class="ident">diag</span> <span class="op">=</span> <span class="ident">b</span>.<span class="ident">span</span>().<span class="ident">unstable</span>()
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.<span class="ident">error</span>(<span class="macro">format</span><span class="macro">!</span>(<span class="string">"expected {} element(s), got {}"</span>, <span class="ident">a_len</span>, <span class="ident">b_len</span>))
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.<span class="ident">span_note</span>(<span class="ident">a</span>.<span class="ident">span</span>().<span class="ident">unstable</span>(), <span class="string">"because of this"</span>);
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<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">diag</span>);
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}
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<span class="comment">// Build the output tokens.</span>
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<span class="kw">let</span> <span class="ident">out</span> <span class="op">=</span> <span class="macro">quote</span><span class="macro">!</span> {
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"All good! Received two tuples of size {}"</span>, #<span class="ident">a_len</span>);
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};
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<span class="prelude-val">Ok</span>(<span class="ident">out</span>.<span class="ident">into</span>())
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}</pre>
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</div><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.Cursor.html"
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title='struct syn::buffer::Cursor'>Cursor</a></td>
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<td class='docblock-short'>
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<p>A cheaply copyable cursor into a <code>TokenBuffer</code>.</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="struct" href="struct.TokenBuffer.html"
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title='struct syn::buffer::TokenBuffer'>TokenBuffer</a></td>
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<td class='docblock-short'>
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<p>A buffer that can be efficiently traversed multiple times, unlike
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<code>TokenStream</code> which requires a deep copy in order to traverse more than
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once.</p>
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</td>
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</tr></table></section>
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<div class="infos">
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<h2>Search Tricks</h2>
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<p>
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Prefix searches with a type followed by a colon (e.g.
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<code>fn:</code>) to restrict the search to a given type.
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</p>
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<p>
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Accepted types are: <code>fn</code>, <code>mod</code>,
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<code>struct</code>, <code>enum</code>,
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<code>trait</code>, <code>type</code>, <code>macro</code>,
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and <code>const</code>.
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</p>
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<p>
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Search functions by type signature (e.g.
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<code>vec -> usize</code> or <code>* -> vec</code>)
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<script>
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window.rootPath = "../../";
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window.currentCrate = "syn";
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</script>
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<script src="../../main.js"></script>
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<script defer src="../../search-index.js"></script>
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