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<h1 class='fqn'><span class='in-band'><a href='index.html'>nom</a>::<wbr><a class='macro' href=''>error!</a></span><span class='out-of-band'><span id='render-detail'>
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</span><a id='src-7384' class='srclink' href='../src/nom/macros.rs.html#201-221' 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'>error</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'>code</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'>=></span> (
{
<span class='kw'>let</span> <span class='ident'>cl</span> <span class='op'>=</span> <span class='op'>||</span> {
<span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>submac</span><span class='op'>!</span>(<span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>i</span>, $(<span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>args</span>)<span class='op'>*</span>)
};
<span class='kw'>match</span> <span class='ident'>cl</span>() {
<span class='comment'>//match cl($i) {</span>
<span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>crate</span>::<span class='ident'>IResult</span>::<span class='ident'>Incomplete</span>(<span class='ident'>x</span>) <span class='op'>=></span> <span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>crate</span>::<span class='ident'>IResult</span>::<span class='ident'>Incomplete</span>(<span class='ident'>x</span>),
<span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>crate</span>::<span class='ident'>IResult</span>::<span class='ident'>Done</span>(<span class='ident'>i</span>, <span class='ident'>o</span>) <span class='op'>=></span> <span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>crate</span>::<span class='ident'>IResult</span>::<span class='ident'>Done</span>(<span class='ident'>i</span>, <span class='ident'>o</span>),
<span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>crate</span>::<span class='ident'>IResult</span>::<span class='ident'>Error</span>(<span class='ident'>e</span>) <span class='op'>=></span> {
<span class='kw'>return</span> <span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>crate</span>::<span class='ident'>IResult</span>::<span class='ident'>Error</span>(<span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>crate</span>::<span class='prelude-val'>Err</span>::<span class='ident'>NodePosition</span>(<span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>code</span>, <span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>i</span>, <span class='ident'>Box</span>::<span class='ident'>new</span>(<span class='ident'>e</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'>code</span>:<span class='ident'>expr</span>, <span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>f</span>:<span class='ident'>expr</span>) <span class='op'>=></span> (
<span class='macro'>error</span><span class='macro'>!</span>(<span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>i</span>, <span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>code</span>, <span class='macro'>call</span><span class='macro'>!</span>(<span class='macro-nonterminal'>$</span><span class='macro-nonterminal'>f</span>));
);
);
</pre>
<div class='docblock'><p>Prevents backtracking if the child parser fails</p>
<p>This parser will do an early return instead of sending
its result to the parent parser.</p>
<p>If another <code>error!</code> combinator is present in the parent
chain, the error will be wrapped and another early
return will be made.</p>
<p>This makes it easy to build report on which parser failed,
where it failed in the input, and the chain of parsers
that led it there.</p>
<p>Additionally, the error chain contains number identifiers
that can be matched to provide useful error messages.</p>
<pre class='rust rust-example-rendered'>
<span class='macro'>named</span><span class='macro'>!</span>(<span class='ident'>err_test</span>, <span class='macro'>alt</span><span class='macro'>!</span>(
<span class='macro'>tag</span><span class='macro'>!</span>(<span class='string'>"abcd"</span>) <span class='op'>|</span>
<span class='macro'>preceded</span><span class='macro'>!</span>(<span class='macro'>tag</span><span class='macro'>!</span>(<span class='string'>"efgh"</span>), <span class='macro'>error</span><span class='macro'>!</span>(<span class='number'>42</span>,
<span class='macro'>chain</span><span class='macro'>!</span>(
<span class='macro'>tag</span><span class='macro'>!</span>(<span class='string'>"ijkl"</span>) <span class='kw-2'>~</span>
<span class='ident'>res</span>: <span class='macro'>error</span><span class='macro'>!</span>(<span class='number'>128</span>, <span class='macro'>tag</span><span class='macro'>!</span>(<span class='string'>"mnop"</span>)) ,
<span class='op'>||</span> { <span class='ident'>res</span> }
)
)
)
));
<span class='kw'>let</span> <span class='ident'>a</span> <span class='op'>=</span> <span class='kw-2'>&</span><span class='string'>b"efghblah"</span>[..];
<span class='kw'>let</span> <span class='ident'>b</span> <span class='op'>=</span> <span class='kw-2'>&</span><span class='string'>b"efghijklblah"</span>[..];
<span class='kw'>let</span> <span class='ident'>c</span> <span class='op'>=</span> <span class='kw-2'>&</span><span class='string'>b"efghijklmnop"</span>[..];
<span class='kw'>let</span> <span class='ident'>blah</span> <span class='op'>=</span> <span class='kw-2'>&</span><span class='string'>b"blah"</span>[..];
<span class='kw'>let</span> <span class='ident'>res_a</span> <span class='op'>=</span> <span class='ident'>err_test</span>(<span class='ident'>a</span>);
<span class='kw'>let</span> <span class='ident'>res_b</span> <span class='op'>=</span> <span class='ident'>err_test</span>(<span class='ident'>b</span>);
<span class='kw'>let</span> <span class='ident'>res_c</span> <span class='op'>=</span> <span class='ident'>err_test</span>(<span class='ident'>c</span>);
<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>res_a</span>, <span class='ident'>Error</span>(<span class='ident'>NodePosition</span>(<span class='number'>42</span>, <span class='ident'>blah</span>, <span class='ident'>Box</span>::<span class='ident'>new</span>(<span class='ident'>Position</span>(<span class='number'>0</span>, <span class='ident'>blah</span>)))));
<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>res_b</span>, <span class='ident'>Error</span>(<span class='ident'>NodePosition</span>(<span class='number'>42</span>, <span class='kw-2'>&</span><span class='string'>b"ijklblah"</span>[..], <span class='ident'>Box</span>::<span class='ident'>new</span>(<span class='ident'>NodePosition</span>(<span class='number'>128</span>, <span class='ident'>blah</span>, <span class='ident'>Box</span>::<span class='ident'>new</span>(<span class='ident'>Position</span>(<span class='number'>0</span>, <span class='ident'>blah</span>)))))));
</pre>
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