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HPC-Tools-for-Quantum-Computing


			
				
					
						
						
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<h1 class='fqn'><span class='in-band'>Macro <a href='index.html'>synom</a>::<wbr><a class="macro" href=''>peek</a></span><span class='out-of-band'><span id='render-detail'>
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               </span><a class='srclink' href='../src/synom/lib.rs.html#625-636' title='goto source code'>[src]</a></span></h1>
<pre class="rust macro">
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">peek</span> {
    (<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">submac</span>:<span class="macro">ident</span><span class="macro">!</span>( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">args</span>:<span class="ident">tt</span>)<span class="op">*</span> )) <span class="op">=&gt;</span> { ... };
    (<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>) <span class="op">=&gt;</span> { ... };
}</pre>
<div class='docblock'><p>Parse a value without consuming it from the input data.</p>
<ul>
<li><strong>Syntax:</strong> <code>peek!(THING)</code></li>
<li><strong>Output:</strong> <code>THING</code></li>
</ul>

<pre class="rust rust-example-rendered">
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">syn</span>;
<span class="attribute">#[<span class="ident">macro_use</span>]</span> <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">synom</span>;

<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">Expr</span>;
<span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">parse</span>::{<span class="ident">ident</span>, <span class="ident">expr</span>};
<span class="kw">use</span> <span class="ident">synom</span>::<span class="ident">IResult</span>;

<span class="comment">// Parse an expression that begins with an identifier.</span>
<span class="macro">named</span><span class="macro">!</span>(<span class="ident">ident_expr</span> <span class="op">-&gt;</span> <span class="ident">Expr</span>,
    <span class="macro">preceded</span><span class="macro">!</span>(<span class="macro">peek</span><span class="macro">!</span>(<span class="ident">ident</span>), <span class="ident">expr</span>)
);

<span class="kw">fn</span> <span class="ident">main</span>() {
    <span class="comment">// begins with an identifier</span>
    <span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="string">&quot;banana + 1&quot;</span>;
    <span class="kw">let</span> <span class="ident">parsed</span> <span class="op">=</span> <span class="ident">ident_expr</span>(<span class="ident">input</span>).<span class="ident">expect</span>(<span class="string">&quot;ident&quot;</span>);
    <span class="macro">println</span><span class="macro">!</span>(<span class="string">&quot;{:?}&quot;</span>, <span class="ident">parsed</span>);

    <span class="comment">// does not begin with an identifier</span>
    <span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="string">&quot;1 + banana&quot;</span>;
    <span class="kw">let</span> <span class="ident">err</span> <span class="op">=</span> <span class="ident">ident_expr</span>(<span class="ident">input</span>);
    <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">err</span>, <span class="ident">IResult</span>::<span class="ident">Error</span>);
}</pre>
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