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|
/// `match` for parsers
///
/// When parsers have unique prefixes to test for, this offers better performance over
/// [`alt`][crate::combinator::alt] though it might be at the cost of duplicating parts of your grammar
/// if you needed to [`peek`][crate::combinator::peek].
///
/// For tight control over the error in a catch-all case, use [`fail`][crate::combinator::fail].
///
/// # Example
///
/// ```rust
/// use winnow::prelude::*;
/// use winnow::combinator::dispatch;
/// # use winnow::token::any;
/// # use winnow::combinator::peek;
/// # use winnow::combinator::preceded;
/// # use winnow::combinator::success;
/// # use winnow::combinator::fail;
///
/// fn escaped(input: &mut &str) -> PResult<char> {
/// preceded('\\', escape_seq_char).parse_next(input)
/// }
///
/// fn escape_seq_char(input: &mut &str) -> PResult<char> {
/// dispatch! {any;
/// 'b' => success('\u{8}'),
/// 'f' => success('\u{c}'),
/// 'n' => success('\n'),
/// 'r' => success('\r'),
/// 't' => success('\t'),
/// '\\' => success('\\'),
/// '"' => success('"'),
/// _ => fail::<_, char, _>,
/// }
/// .parse_next(input)
/// }
///
/// assert_eq!(escaped.parse_peek("\\nHello"), Ok(("Hello", '\n')));
/// ```
#[macro_export]
#[doc(hidden)] // forced to be visible in intended location
macro_rules! dispatch {
($match_parser: expr; $( $pat:pat $(if $pred:expr)? => $expr: expr ),+ $(,)? ) => {
$crate::trace::trace("dispatch", move |i: &mut _|
{
use $crate::Parser;
let initial = $match_parser.parse_next(i)?;
match initial {
$(
$pat $(if $pred)? => $expr.parse_next(i),
)*
}
})
}
}
macro_rules! succ (
(0, $submac:ident ! ($($rest:tt)*)) => ($submac!(1, $($rest)*));
(1, $submac:ident ! ($($rest:tt)*)) => ($submac!(2, $($rest)*));
(2, $submac:ident ! ($($rest:tt)*)) => ($submac!(3, $($rest)*));
(3, $submac:ident ! ($($rest:tt)*)) => ($submac!(4, $($rest)*));
(4, $submac:ident ! ($($rest:tt)*)) => ($submac!(5, $($rest)*));
(5, $submac:ident ! ($($rest:tt)*)) => ($submac!(6, $($rest)*));
(6, $submac:ident ! ($($rest:tt)*)) => ($submac!(7, $($rest)*));
(7, $submac:ident ! ($($rest:tt)*)) => ($submac!(8, $($rest)*));
(8, $submac:ident ! ($($rest:tt)*)) => ($submac!(9, $($rest)*));
(9, $submac:ident ! ($($rest:tt)*)) => ($submac!(10, $($rest)*));
(10, $submac:ident ! ($($rest:tt)*)) => ($submac!(11, $($rest)*));
(11, $submac:ident ! ($($rest:tt)*)) => ($submac!(12, $($rest)*));
(12, $submac:ident ! ($($rest:tt)*)) => ($submac!(13, $($rest)*));
(13, $submac:ident ! ($($rest:tt)*)) => ($submac!(14, $($rest)*));
(14, $submac:ident ! ($($rest:tt)*)) => ($submac!(15, $($rest)*));
(15, $submac:ident ! ($($rest:tt)*)) => ($submac!(16, $($rest)*));
(16, $submac:ident ! ($($rest:tt)*)) => ($submac!(17, $($rest)*));
(17, $submac:ident ! ($($rest:tt)*)) => ($submac!(18, $($rest)*));
(18, $submac:ident ! ($($rest:tt)*)) => ($submac!(19, $($rest)*));
(19, $submac:ident ! ($($rest:tt)*)) => ($submac!(20, $($rest)*));
(20, $submac:ident ! ($($rest:tt)*)) => ($submac!(21, $($rest)*));
);
|
