//! Choice combinators
#[cfg(test)]
mod tests;
use crate::error::ErrorKind;
use crate::error::ParseError;
use crate::internal::{Err, IResult, Parser};
/// Helper trait for the [alt()] combinator.
///
/// This trait is implemented for tuples of up to 21 elements
pub trait Alt<I, O, E> {
/// Tests each parser in the tuple and returns the result of the first one that succeeds
fn choice(&mut self, input: I) -> IResult<I, O, E>;
}
/// Tests a list of parsers one by one until one succeeds.
///
/// It takes as argument a tuple of parsers. There is a maximum of 21
/// parsers. If you need more, it is possible to nest them in other `alt` calls,
/// like this: `alt(parser_a, alt(parser_b, parser_c))`
///
/// ```rust
/// # use nom::error_position;
/// # use nom::{Err,error::ErrorKind, Needed, IResult};
/// use nom::character::complete::{alpha1, digit1};
/// use nom::branch::alt;
/// # fn main() {
/// fn parser(input: &str) -> IResult<&str, &str> {
/// alt((alpha1, digit1))(input)
/// };
///
/// // the first parser, alpha1, recognizes the input
/// assert_eq!(parser("abc"), Ok(("", "abc")));
///
/// // the first parser returns an error, so alt tries the second one
/// assert_eq!(parser("123456"), Ok(("", "123456")));
///
/// // both parsers failed, and with the default error type, alt will return the last error
/// assert_eq!(parser(" "), Err(Err::Error(error_position!(" ", ErrorKind::Digit))));
/// # }
/// ```
///
/// With a custom error type, it is possible to have alt return the error of the parser
/// that went the farthest in the input data
pub fn alt<I: Clone, O, E: ParseError<I>, List: Alt<I, O, E>>(
mut l: List,
) -> impl FnMut(I) -> IResult<I, O, E> {
move |i: I| l.choice(i)
}
/// Helper trait for the [permutation()] combinator.
///
/// This trait is implemented for tuples of up to 21 elements
pub trait Permutation<I, O, E> {
/// Tries to apply all parsers in the tuple in various orders until all of them succeed
fn permutation(&mut self, input: I) -> IResult<I, O, E>;
}
/// Applies a list of parsers in any order.
///
/// Permutation will succeed if all of the child parsers succeeded.
/// It takes as argument a tuple of parsers, and returns a
/// tuple of the parser results.
///
/// ```rust
/// # use nom::{Err,error::{Error, ErrorKind}, Needed, IResult};
/// use nom::character::complete::{alpha1, digit1};
/// use nom::branch::permutation;
/// # fn main() {
/// fn parser(input: &str) -> IResult<&str, (&str, &str)> {
/// permutation((alpha1, digit1))(input)
/// }
///
/// // permutation recognizes alphabetic characters then digit
/// assert_eq!(parser("abc123"), Ok(("", ("abc", "123"))));
///
/// // but also in inverse order
/// assert_eq!(parser("123abc"), Ok(("", ("abc", "123"))));
///
/// // it will fail if one of the parsers failed
/// assert_eq!(parser("abc;"), Err(Err::Error(Error::new(";", ErrorKind::Digit))));
/// # }
/// ```
///
/// The parsers are applied greedily: if there are multiple unapplied parsers
/// that could parse the next slice of input, the first one is used.
/// ```rust
/// # use nom::{Err, error::{Error, ErrorKind}, IResult};
/// use nom::branch::permutation;
/// use nom::character::complete::{anychar, char};
///
/// fn parser(input: &str) -> IResult<&str, (char, char)> {
/// permutation((anychar, char('a')))(input)
/// }
///
/// // anychar parses 'b', then char('a') parses 'a'
/// assert_eq!(parser("ba"), Ok(("", ('b', 'a'))));
///
/// // anychar parses 'a', then char('a') fails on 'b',
/// // even though char('a') followed by anychar would succeed
/// assert_eq!(parser("ab"), Err(Err::Error(Error::new("b", ErrorKind::Char))));
/// ```
///
pub fn permutation<I: Clone, O, E: ParseError<I>, List: Permutation<I, O, E>>(
mut l: List,
) -> impl FnMut(I) -> IResult<I, O, E> {
move |i: I| l.permutation(i)
}
macro_rules! alt_trait(
($first:ident $second:ident $($id: ident)+) => (
alt_trait!(__impl $first $second; $($id)+);
);
(__impl $($current:ident)*; $head:ident $($id: ident)+) => (
alt_trait_impl!($($current)*);
alt_trait!(__impl $($current)* $head; $($id)+);
);
(__impl $($current:ident)*; $head:ident) => (
alt_trait_impl!($($current)*);
alt_trait_impl!($($current)* $head);
);
);
macro_rules! alt_trait_impl(
($($id:ident)+) => (
impl<
Input: Clone, Output, Error: ParseError<Input>,
$($id: Parser<Input, Output, Error>),+
> Alt<Input, Output, Error> for ( $($id),+ ) {
fn choice(&mut self, input: Input) -> IResult<Input, Output, Error> {
match self.0.parse(input.clone()) {
Err(Err::Error(e)) => alt_trait_inner!(1, self, input, e, $($id)+),
res => res,
}
}
}
);
);
macro_rules! alt_trait_inner(
($it:tt, $self:expr, $input:expr, $err:expr, $head:ident $($id:ident)+) => (
match $self.$it.parse($input.clone()) {
Err(Err::Error(e)) => {
let err = $err.or(e);
succ!($it, alt_trait_inner!($self, $input, err, $($id)+))
}
res => res,
}
);
($it:tt, $self:expr, $input:expr, $err:expr, $head:ident) => (
Err(Err::Error(Error::append($input, ErrorKind::Alt, $err)))
);
);
alt_trait!(A B C D E F G H I J K L M N O P Q R S T U);
// Manually implement Alt for (A,), the 1-tuple type
impl<Input, Output, Error: ParseError<Input>, A: Parser<Input, Output, Error>>
Alt<Input, Output, Error> for (A,)
{
fn choice(&mut self, input: Input) -> IResult<Input, Output, Error> {
self.0.parse(input)
}
}
macro_rules! permutation_trait(
(
$name1:ident $ty1:ident $item1:ident
$name2:ident $ty2:ident $item2:ident
$($name3:ident $ty3:ident $item3:ident)*
) => (
permutation_trait!(__impl $name1 $ty1 $item1, $name2 $ty2 $item2; $($name3 $ty3 $item3)*);
);
(
__impl $($name:ident $ty:ident $item:ident),+;
$name1:ident $ty1:ident $item1:ident $($name2:ident $ty2:ident $item2:ident)*
) => (
permutation_trait_impl!($($name $ty $item),+);
permutation_trait!(__impl $($name $ty $item),+ , $name1 $ty1 $item1; $($name2 $ty2 $item2)*);
);
(__impl $($name:ident $ty:ident $item:ident),+;) => (
permutation_trait_impl!($($name $ty $item),+);
);
);
macro_rules! permutation_trait_impl(
($($name:ident $ty:ident $item:ident),+) => (
impl<
Input: Clone, $($ty),+ , Error: ParseError<Input>,
$($name: Parser<Input, $ty, Error>),+
> Permutation<Input, ( $($ty),+ ), Error> for ( $($name),+ ) {
fn permutation(&mut self, mut input: Input) -> IResult<Input, ( $($ty),+ ), Error> {
let mut res = ($(Option::<$ty>::None),+);
loop {
let mut err: Option<Error> = None;
permutation_trait_inner!(0, self, input, res, err, $($name)+);
// If we reach here, every iterator has either been applied before,
// or errored on the remaining input
if let Some(err) = err {
// There are remaining parsers, and all errored on the remaining input
return Err(Err::Error(Error::append(input, ErrorKind::Permutation, err)));
}
// All parsers were applied
match res {
($(Some($item)),+) => return Ok((input, ($($item),+))),
_ => unreachable!(),
}
}
}
}
);
);
macro_rules! permutation_trait_inner(
($it:tt, $self:expr, $input:ident, $res:expr, $err:expr, $head:ident $($id:ident)*) => (
if $res.$it.is_none() {
match $self.$it.parse($input.clone()) {
Ok((i, o)) => {
$input = i;
$res.$it = Some(o);
continue;
}
Err(Err::Error(e)) => {
$err = Some(match $err {
Some(err) => err.or(e),
None => e,
});
}
Err(e) => return Err(e),
};
}
succ!($it, permutation_trait_inner!($self, $input, $res, $err, $($id)*));
);
($it:tt, $self:expr, $input:ident, $res:expr, $err:expr,) => ();
);
permutation_trait!(
FnA A a
FnB B b
FnC C c
FnD D d
FnE E e
FnF F f
FnG G g
FnH H h
FnI I i
FnJ J j
FnK K k
FnL L l
FnM M m
FnN N n
FnO O o
FnP P p
FnQ Q q
FnR R r
FnS S s
FnT T t
FnU U u
);
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