src/combinator/core.rs - platform/external/rust/crates/winnow - Gitiles

 use crate::combinator::trace;
 use crate::error::{ErrMode, ErrorKind, Needed, ParserError};
 use crate::stream::Stream;
 use crate::*;

 /// Return the remaining input.
 ///
 /// # Example
 ///
 /// ```rust
 /// # use winnow::prelude::*;
 /// # use winnow::error::ErrorKind;
 /// # use winnow::error::InputError;
 /// use winnow::combinator::rest;
 /// assert_eq!(rest::<_,InputError<_>>.parse_peek("abc"), Ok(("", "abc")));
 /// assert_eq!(rest::<_,InputError<_>>.parse_peek(""), Ok(("", "")));
 /// ```
 #[inline]
 pub fn rest<I, E: ParserError<I>>(input: &mut I) -> PResult<<I as Stream>::Slice, E>
 where
     I: Stream,
 {
     trace("rest", move |input: &mut I| Ok(input.finish())).parse_next(input)
 }

 /// Return the length of the remaining input.
 ///
 /// Note: this does not advance the [`Stream`]
 ///
 /// # Example
 ///
 /// ```rust
 /// # use winnow::prelude::*;
 /// # use winnow::error::ErrorKind;
 /// # use winnow::error::InputError;
 /// use winnow::combinator::rest_len;
 /// assert_eq!(rest_len::<_,InputError<_>>.parse_peek("abc"), Ok(("abc", 3)));
 /// assert_eq!(rest_len::<_,InputError<_>>.parse_peek(""), Ok(("", 0)));
 /// ```
 #[inline]
 pub fn rest_len<I, E: ParserError<I>>(input: &mut I) -> PResult<usize, E>
 where
     I: Stream,
 {
     trace("rest_len", move |input: &mut I| {
         let len = input.eof_offset();
         Ok(len)
     })
     .parse_next(input)
 }

 /// Apply a [`Parser`], producing `None` on [`ErrMode::Backtrack`].
 ///
 /// To chain an error up, see [`cut_err`].
 ///
 /// # Example
 ///
 /// ```rust
 /// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError};
 /// # use winnow::prelude::*;
 /// use winnow::combinator::opt;
 /// use winnow::ascii::alpha1;
 /// # fn main() {
 ///
 /// fn parser(i: &str) -> IResult<&str, Option<&str>> {
 ///   opt(alpha1).parse_peek(i)
 /// }
 ///
 /// assert_eq!(parser("abcd;"), Ok((";", Some("abcd"))));
 /// assert_eq!(parser("123;"), Ok(("123;", None)));
 /// # }
 /// ```
 pub fn opt<I: Stream, O, E: ParserError<I>, F>(mut f: F) -> impl Parser<I, Option<O>, E>
 where
     F: Parser<I, O, E>,
 {
     trace("opt", move |input: &mut I| {
         let start = input.checkpoint();
         match f.parse_next(input) {
             Ok(o) => Ok(Some(o)),
             Err(ErrMode::Backtrack(_)) => {
                 input.reset(start);
                 Ok(None)
             }
             Err(e) => Err(e),
         }
     })
 }

 /// Calls the parser if the condition is met.
 ///
 /// # Example
 ///
 /// ```rust
 /// # use winnow::{error::ErrMode, error::{InputError, ErrorKind}, IResult};
 /// # use winnow::prelude::*;
 /// use winnow::combinator::cond;
 /// use winnow::ascii::alpha1;
 /// # fn main() {
 ///
 /// fn parser(b: bool, i: &str) -> IResult<&str, Option<&str>> {
 ///   cond(b, alpha1).parse_peek(i)
 /// }
 ///
 /// assert_eq!(parser(true, "abcd;"), Ok((";", Some("abcd"))));
 /// assert_eq!(parser(false, "abcd;"), Ok(("abcd;", None)));
 /// assert_eq!(parser(true, "123;"), Err(ErrMode::Backtrack(InputError::new("123;", ErrorKind::Slice))));
 /// assert_eq!(parser(false, "123;"), Ok(("123;", None)));
 /// # }
 /// ```
 pub fn cond<I, O, E: ParserError<I>, F>(b: bool, mut f: F) -> impl Parser<I, Option<O>, E>
 where
     I: Stream,
     F: Parser<I, O, E>,
 {
     trace("cond", move |input: &mut I| {
         if b {
             f.parse_next(input).map(Some)
         } else {
             Ok(None)
         }
     })
 }

 /// Tries to apply its parser without consuming the input.
 ///
 /// # Example
 ///
 /// ```rust
 /// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError, IResult};
 /// # use winnow::prelude::*;
 /// use winnow::combinator::peek;
 /// use winnow::ascii::alpha1;
 /// # fn main() {
 ///
 /// let mut parser = peek(alpha1);
 ///
 /// assert_eq!(parser.parse_peek("abcd;"), Ok(("abcd;", "abcd")));
 /// assert_eq!(parser.parse_peek("123;"), Err(ErrMode::Backtrack(InputError::new("123;", ErrorKind::Slice))));
 /// # }
 /// ```
 #[doc(alias = "look_ahead")]
 #[doc(alias = "rewind")]
 pub fn peek<I: Stream, O, E: ParserError<I>, F>(mut f: F) -> impl Parser<I, O, E>
 where
     F: Parser<I, O, E>,
 {
     trace("peek", move |input: &mut I| {
         let start = input.checkpoint();
         let res = f.parse_next(input);
         input.reset(start);
         res
     })
 }

 /// Match the end of the [`Stream`]
 ///
 /// Otherwise, it will error.
 ///
 /// # Example
 ///
 /// ```rust
 /// # use std::str;
 /// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError};
 /// # use winnow::combinator::eof;
 /// # use winnow::prelude::*;
 ///
 /// let mut parser = eof;
 /// assert_eq!(parser.parse_peek("abc"), Err(ErrMode::Backtrack(InputError::new("abc", ErrorKind::Eof))));
 /// assert_eq!(parser.parse_peek(""), Ok(("", "")));
 /// ```
 #[doc(alias = "end")]
 #[doc(alias = "eoi")]
 pub fn eof<I, E: ParserError<I>>(input: &mut I) -> PResult<<I as Stream>::Slice, E>
 where
     I: Stream,
 {
     trace("eof", move |input: &mut I| {
         if input.eof_offset() == 0 {
             Ok(input.next_slice(0))
         } else {
             Err(ErrMode::from_error_kind(input, ErrorKind::Eof))
         }
     })
     .parse_next(input)
 }

 /// Succeeds if the child parser returns an error.
 ///
 /// **Note:** This does not advance the [`Stream`]
 ///
 /// # Example
 ///
 /// ```rust
 /// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError, IResult};
 /// # use winnow::prelude::*;
 /// use winnow::combinator::not;
 /// use winnow::ascii::alpha1;
 /// # fn main() {
 ///
 /// let mut parser = not(alpha1);
 ///
 /// assert_eq!(parser.parse_peek("123"), Ok(("123", ())));
 /// assert_eq!(parser.parse_peek("abcd"), Err(ErrMode::Backtrack(InputError::new("abcd", ErrorKind::Not))));
 /// # }
 /// ```
 pub fn not<I: Stream, O, E: ParserError<I>, F>(mut parser: F) -> impl Parser<I, (), E>
 where
     F: Parser<I, O, E>,
 {
     trace("not", move |input: &mut I| {
         let start = input.checkpoint();
         let res = parser.parse_next(input);
         input.reset(start);
         match res {
             Ok(_) => Err(ErrMode::from_error_kind(input, ErrorKind::Not)),
             Err(ErrMode::Backtrack(_)) => Ok(()),
             Err(e) => Err(e),
         }
     })
 }

 /// Transforms an [`ErrMode::Backtrack`] (recoverable) to [`ErrMode::Cut`] (unrecoverable)
 ///
 /// This commits the parse result, preventing alternative branch paths like with
 /// [`winnow::combinator::alt`][crate::combinator::alt].
 ///
 /// See the [tutorial][crate::_tutorial::chapter_6] for more details.
 ///
 /// # Example
 ///
 /// Without `cut_err`:
 /// ```rust
 /// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError};
 /// # use winnow::token::one_of;
 /// # use winnow::ascii::digit1;
 /// # use winnow::combinator::rest;
 /// # use winnow::combinator::alt;
 /// # use winnow::combinator::preceded;
 /// # use winnow::prelude::*;
 /// # fn main() {
 ///
 /// fn parser(input: &str) -> IResult<&str, &str> {
 ///   alt((
 ///     preceded(one_of(['+', '-']), digit1),
 ///     rest
 ///   )).parse_peek(input)
 /// }
 ///
 /// assert_eq!(parser("+10 ab"), Ok((" ab", "10")));
 /// assert_eq!(parser("ab"), Ok(("", "ab")));
 /// assert_eq!(parser("+"), Ok(("", "+")));
 /// # }
 /// ```
 ///
 /// With `cut_err`:
 /// ```rust
 /// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError};
 /// # use winnow::prelude::*;
 /// # use winnow::token::one_of;
 /// # use winnow::ascii::digit1;
 /// # use winnow::combinator::rest;
 /// # use winnow::combinator::alt;
 /// # use winnow::combinator::preceded;
 /// use winnow::combinator::cut_err;
 /// # fn main() {
 ///
 /// fn parser(input: &str) -> IResult<&str, &str> {
 ///   alt((
 ///     preceded(one_of(['+', '-']), cut_err(digit1)),
 ///     rest
 ///   )).parse_peek(input)
 /// }
 ///
 /// assert_eq!(parser("+10 ab"), Ok((" ab", "10")));
 /// assert_eq!(parser("ab"), Ok(("", "ab")));
 /// assert_eq!(parser("+"), Err(ErrMode::Cut(InputError::new("", ErrorKind::Slice ))));
 /// # }
 /// ```
 pub fn cut_err<I, O, E: ParserError<I>, F>(mut parser: F) -> impl Parser<I, O, E>
 where
     I: Stream,
     F: Parser<I, O, E>,
 {
     trace("cut_err", move |input: &mut I| {
         parser.parse_next(input).map_err(|e| e.cut())
     })
 }

 /// Transforms an [`ErrMode::Cut`] (unrecoverable) to [`ErrMode::Backtrack`] (recoverable)
 ///
 /// This attempts the parse, allowing other parsers to be tried on failure, like with
 /// [`winnow::combinator::alt`][crate::combinator::alt].
 pub fn backtrack_err<I, O, E: ParserError<I>, F>(mut parser: F) -> impl Parser<I, O, E>
 where
     I: Stream,
     F: Parser<I, O, E>,
 {
     trace("backtrack_err", move |input: &mut I| {
         parser.parse_next(input).map_err(|e| e.backtrack())
     })
 }

 /// A placeholder for a not-yet-implemented [`Parser`]
 ///
 /// This is analogous to the [`todo!`] macro and helps with prototyping.
 ///
 /// # Panic
 ///
 /// This will panic when parsing
 ///
 /// # Example
 ///
 /// ```rust
 /// # use winnow::prelude::*;
 /// # use winnow::combinator::todo;
 ///
 /// fn parser(input: &mut &str) -> PResult<u64> {
 ///     todo(input)
 /// }
 /// ```
 #[track_caller]
 pub fn todo<I, O, E>(input: &mut I) -> PResult<O, E>
 where
     I: Stream,
 {
     #![allow(clippy::todo)]
     trace("todo", move |_input: &mut I| todo!("unimplemented parse")).parse_next(input)
 }

 /// Repeats the embedded parser, lazily returning the results
 ///
 /// Call the iterator's [`ParserIterator::finish`] method to get the remaining input if successful,
 /// or the error value if we encountered an error.
 ///
 /// On [`ErrMode::Backtrack`], iteration will stop. To instead chain an error up, see [`cut_err`].
 ///
 /// # Example
 ///
 /// ```rust
 /// use winnow::{combinator::iterator, IResult, token::tag, ascii::alpha1, combinator::terminated};
 /// use std::collections::HashMap;
 ///
 /// let data = "abc|defg|hijkl|mnopqr|123";
 /// let mut it = iterator(data, terminated(alpha1, "|"));
 ///
 /// let parsed = it.map(|v| (v, v.len())).collect::<HashMap<_,_>>();
 /// let res: IResult<_,_> = it.finish();
 ///
 /// assert_eq!(parsed, [("abc", 3usize), ("defg", 4), ("hijkl", 5), ("mnopqr", 6)].iter().cloned().collect());
 /// assert_eq!(res, Ok(("123", ())));
 /// ```
 pub fn iterator<I, O, E, F>(input: I, parser: F) -> ParserIterator<F, I, O, E>
 where
     F: Parser<I, O, E>,
     I: Stream,
     E: ParserError<I>,
 {
     ParserIterator {
         parser,
         input,
         state: Some(State::Running),
         o: Default::default(),
     }
 }

 /// Main structure associated to [`iterator`].
 pub struct ParserIterator<F, I, O, E>
 where
     F: Parser<I, O, E>,
     I: Stream,
 {
     parser: F,
     input: I,
     state: Option<State<E>>,
     o: core::marker::PhantomData<O>,
 }

 impl<F, I, O, E> ParserIterator<F, I, O, E>
 where
     F: Parser<I, O, E>,
     I: Stream,
 {
     /// Returns the remaining input if parsing was successful, or the error if we encountered an error.
     pub fn finish(mut self) -> PResult<(I, ()), E> {
         match self.state.take().unwrap() {
             State::Running | State::Done => Ok((self.input, ())),
             State::Failure(e) => Err(ErrMode::Cut(e)),
             State::Incomplete(i) => Err(ErrMode::Incomplete(i)),
         }
     }
 }

 impl<'a, F, I, O, E> core::iter::Iterator for &'a mut ParserIterator<F, I, O, E>
 where
     F: Parser<I, O, E>,
     I: Stream,
 {
     type Item = O;

     fn next(&mut self) -> Option<Self::Item> {
         if let State::Running = self.state.take().unwrap() {
             let start = self.input.checkpoint();

             match self.parser.parse_next(&mut self.input) {
                 Ok(o) => {
                     self.state = Some(State::Running);
                     Some(o)
                 }
                 Err(ErrMode::Backtrack(_)) => {
                     self.input.reset(start);
                     self.state = Some(State::Done);
                     None
                 }
                 Err(ErrMode::Cut(e)) => {
                     self.state = Some(State::Failure(e));
                     None
                 }
                 Err(ErrMode::Incomplete(i)) => {
                     self.state = Some(State::Incomplete(i));
                     None
                 }
             }
         } else {
             None
         }
     }
 }

 enum State<E> {
     Running,
     Done,
     Failure(E),
     Incomplete(Needed),
 }

 /// Succeed, consuming no input
 ///
 /// For example, it can be used as the last alternative in `alt` to
 /// specify the default case.
 ///
 /// Useful with:
 /// - [`Parser::value`]
 /// - [`Parser::default_value`]
 /// - [`Parser::map`]
 ///
 /// **Note:** This never advances the [`Stream`]
 ///
 /// # Example
 ///
 /// ```rust
 /// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError};
 /// # use winnow::prelude::*;
 /// use winnow::combinator::alt;
 /// use winnow::combinator::empty;
 ///
 /// fn sign(input: &str) -> IResult<&str, isize> {
 ///     alt((
 ///         '-'.value(-1),
 ///         '+'.value(1),
 ///         empty.value(1)
 ///     )).parse_peek(input)
 /// }
 /// assert_eq!(sign("+10"), Ok(("10", 1)));
 /// assert_eq!(sign("-10"), Ok(("10", -1)));
 /// assert_eq!(sign("10"), Ok(("10", 1)));
 /// ```
 #[doc(alias = "value")]
 #[doc(alias = "success")]
 pub fn empty<I: Stream, E: ParserError<I>>(_input: &mut I) -> PResult<(), E> {
     Ok(())
 }

 /// Deprecated, replaced with [`empty`] + [`Parser::value`]
 #[deprecated(since = "0.5.35", note = "Replaced with empty.value(...)`")]
 pub fn success<I: Stream, O: Clone, E: ParserError<I>>(val: O) -> impl Parser<I, O, E> {
     trace("success", move |_input: &mut I| Ok(val.clone()))
 }

 /// A parser which always fails.
 ///
 /// For example, it can be used as the last alternative in `alt` to
 /// control the error message given.
 ///
 /// # Example
 ///
 /// ```rust
 /// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError, IResult};
 /// # use winnow::prelude::*;
 /// use winnow::combinator::fail;
 ///
 /// let s = "string";
 /// assert_eq!(fail::<_, &str, _>.parse_peek(s), Err(ErrMode::Backtrack(InputError::new(s, ErrorKind::Fail))));
 /// ```
 #[doc(alias = "unexpected")]
 pub fn fail<I: Stream, O, E: ParserError<I>>(i: &mut I) -> PResult<O, E> {
     trace("fail", |i: &mut I| {
         Err(ErrMode::from_error_kind(i, ErrorKind::Fail))
     })
     .parse_next(i)
 }
	use crate::combinator::trace;
	use crate::error::{ErrMode, ErrorKind, Needed, ParserError};
	use crate::stream::Stream;
	use crate::*;

	/// Return the remaining input.
	///
	/// # Example
	///
	/// ```rust
	/// # use winnow::prelude::*;
	/// # use winnow::error::ErrorKind;
	/// # use winnow::error::InputError;
	/// use winnow::combinator::rest;
	/// assert_eq!(rest::<_,InputError<_>>.parse_peek("abc"), Ok(("", "abc")));
	/// assert_eq!(rest::<_,InputError<_>>.parse_peek(""), Ok(("", "")));
	/// ```
	#[inline]
	pub fn rest<I, E: ParserError<I>>(input: &mut I) -> PResult<<I as Stream>::Slice, E>
	where
	I: Stream,
	{
	trace("rest", move \|input: &mut I\| Ok(input.finish())).parse_next(input)
	}

	/// Return the length of the remaining input.
	///
	/// Note: this does not advance the [`Stream`]
	///
	/// # Example
	///
	/// ```rust
	/// # use winnow::prelude::*;
	/// # use winnow::error::ErrorKind;
	/// # use winnow::error::InputError;
	/// use winnow::combinator::rest_len;
	/// assert_eq!(rest_len::<_,InputError<_>>.parse_peek("abc"), Ok(("abc", 3)));
	/// assert_eq!(rest_len::<_,InputError<_>>.parse_peek(""), Ok(("", 0)));
	/// ```
	#[inline]
	pub fn rest_len<I, E: ParserError<I>>(input: &mut I) -> PResult<usize, E>
	where
	I: Stream,
	{
	trace("rest_len", move \|input: &mut I\| {
	let len = input.eof_offset();
	Ok(len)
	})
	.parse_next(input)
	}

	/// Apply a [`Parser`], producing `None` on [`ErrMode::Backtrack`].
	///
	/// To chain an error up, see [`cut_err`].
	///
	/// # Example
	///
	/// ```rust
	/// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError};
	/// # use winnow::prelude::*;
	/// use winnow::combinator::opt;
	/// use winnow::ascii::alpha1;
	/// # fn main() {
	///
	/// fn parser(i: &str) -> IResult<&str, Option<&str>> {
	/// opt(alpha1).parse_peek(i)
	/// }
	///
	/// assert_eq!(parser("abcd;"), Ok((";", Some("abcd"))));
	/// assert_eq!(parser("123;"), Ok(("123;", None)));
	/// # }
	/// ```
	pub fn opt<I: Stream, O, E: ParserError<I>, F>(mut f: F) -> impl Parser<I, Option<O>, E>
	where
	F: Parser<I, O, E>,
	{
	trace("opt", move \|input: &mut I\| {
	let start = input.checkpoint();
	match f.parse_next(input) {
	Ok(o) => Ok(Some(o)),
	Err(ErrMode::Backtrack(_)) => {
	input.reset(start);
	Ok(None)
	}
	Err(e) => Err(e),
	}
	})
	}

	/// Calls the parser if the condition is met.
	///
	/// # Example
	///
	/// ```rust
	/// # use winnow::{error::ErrMode, error::{InputError, ErrorKind}, IResult};
	/// # use winnow::prelude::*;
	/// use winnow::combinator::cond;
	/// use winnow::ascii::alpha1;
	/// # fn main() {
	///
	/// fn parser(b: bool, i: &str) -> IResult<&str, Option<&str>> {
	/// cond(b, alpha1).parse_peek(i)
	/// }
	///
	/// assert_eq!(parser(true, "abcd;"), Ok((";", Some("abcd"))));
	/// assert_eq!(parser(false, "abcd;"), Ok(("abcd;", None)));
	/// assert_eq!(parser(true, "123;"), Err(ErrMode::Backtrack(InputError::new("123;", ErrorKind::Slice))));
	/// assert_eq!(parser(false, "123;"), Ok(("123;", None)));
	/// # }
	/// ```
	pub fn cond<I, O, E: ParserError<I>, F>(b: bool, mut f: F) -> impl Parser<I, Option<O>, E>
	where
	I: Stream,
	F: Parser<I, O, E>,
	{
	trace("cond", move \|input: &mut I\| {
	if b {
	f.parse_next(input).map(Some)
	} else {
	Ok(None)
	}
	})
	}

	/// Tries to apply its parser without consuming the input.
	///
	/// # Example
	///
	/// ```rust
	/// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError, IResult};
	/// # use winnow::prelude::*;
	/// use winnow::combinator::peek;
	/// use winnow::ascii::alpha1;
	/// # fn main() {
	///
	/// let mut parser = peek(alpha1);
	///
	/// assert_eq!(parser.parse_peek("abcd;"), Ok(("abcd;", "abcd")));
	/// assert_eq!(parser.parse_peek("123;"), Err(ErrMode::Backtrack(InputError::new("123;", ErrorKind::Slice))));
	/// # }
	/// ```
	#[doc(alias = "look_ahead")]
	#[doc(alias = "rewind")]
	pub fn peek<I: Stream, O, E: ParserError<I>, F>(mut f: F) -> impl Parser<I, O, E>
	where
	F: Parser<I, O, E>,
	{
	trace("peek", move \|input: &mut I\| {
	let start = input.checkpoint();
	let res = f.parse_next(input);
	input.reset(start);
	res
	})
	}

	/// Match the end of the [`Stream`]
	///
	/// Otherwise, it will error.
	///
	/// # Example
	///
	/// ```rust
	/// # use std::str;
	/// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError};
	/// # use winnow::combinator::eof;
	/// # use winnow::prelude::*;
	///
	/// let mut parser = eof;
	/// assert_eq!(parser.parse_peek("abc"), Err(ErrMode::Backtrack(InputError::new("abc", ErrorKind::Eof))));
	/// assert_eq!(parser.parse_peek(""), Ok(("", "")));
	/// ```
	#[doc(alias = "end")]
	#[doc(alias = "eoi")]
	pub fn eof<I, E: ParserError<I>>(input: &mut I) -> PResult<<I as Stream>::Slice, E>
	where
	I: Stream,
	{
	trace("eof", move \|input: &mut I\| {
	if input.eof_offset() == 0 {
	Ok(input.next_slice(0))
	} else {
	Err(ErrMode::from_error_kind(input, ErrorKind::Eof))
	}
	})
	.parse_next(input)
	}

	/// Succeeds if the child parser returns an error.
	///
	/// Note: This does not advance the [`Stream`]
	///
	/// # Example
	///
	/// ```rust
	/// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError, IResult};
	/// # use winnow::prelude::*;
	/// use winnow::combinator::not;
	/// use winnow::ascii::alpha1;
	/// # fn main() {
	///
	/// let mut parser = not(alpha1);
	///
	/// assert_eq!(parser.parse_peek("123"), Ok(("123", ())));
	/// assert_eq!(parser.parse_peek("abcd"), Err(ErrMode::Backtrack(InputError::new("abcd", ErrorKind::Not))));
	/// # }
	/// ```
	pub fn not<I: Stream, O, E: ParserError<I>, F>(mut parser: F) -> impl Parser<I, (), E>
	where
	F: Parser<I, O, E>,
	{
	trace("not", move \|input: &mut I\| {
	let start = input.checkpoint();
	let res = parser.parse_next(input);
	input.reset(start);
	match res {
	Ok(_) => Err(ErrMode::from_error_kind(input, ErrorKind::Not)),
	Err(ErrMode::Backtrack(_)) => Ok(()),
	Err(e) => Err(e),
	}
	})
	}

	/// Transforms an [`ErrMode::Backtrack`] (recoverable) to [`ErrMode::Cut`] (unrecoverable)
	///
	/// This commits the parse result, preventing alternative branch paths like with
	/// [`winnow::combinator::alt`][crate::combinator::alt].
	///
	/// See the [tutorial][crate::_tutorial::chapter_6] for more details.
	///
	/// # Example
	///
	/// Without `cut_err`:
	/// ```rust
	/// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError};
	/// # use winnow::token::one_of;
	/// # use winnow::ascii::digit1;
	/// # use winnow::combinator::rest;
	/// # use winnow::combinator::alt;
	/// # use winnow::combinator::preceded;
	/// # use winnow::prelude::*;
	/// # fn main() {
	///
	/// fn parser(input: &str) -> IResult<&str, &str> {
	/// alt((
	/// preceded(one_of(['+', '-']), digit1),
	/// rest
	/// )).parse_peek(input)
	/// }
	///
	/// assert_eq!(parser("+10 ab"), Ok((" ab", "10")));
	/// assert_eq!(parser("ab"), Ok(("", "ab")));
	/// assert_eq!(parser("+"), Ok(("", "+")));
	/// # }
	/// ```
	///
	/// With `cut_err`:
	/// ```rust
	/// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError};
	/// # use winnow::prelude::*;
	/// # use winnow::token::one_of;
	/// # use winnow::ascii::digit1;
	/// # use winnow::combinator::rest;
	/// # use winnow::combinator::alt;
	/// # use winnow::combinator::preceded;
	/// use winnow::combinator::cut_err;
	/// # fn main() {
	///
	/// fn parser(input: &str) -> IResult<&str, &str> {
	/// alt((
	/// preceded(one_of(['+', '-']), cut_err(digit1)),
	/// rest
	/// )).parse_peek(input)
	/// }
	///
	/// assert_eq!(parser("+10 ab"), Ok((" ab", "10")));
	/// assert_eq!(parser("ab"), Ok(("", "ab")));
	/// assert_eq!(parser("+"), Err(ErrMode::Cut(InputError::new("", ErrorKind::Slice ))));
	/// # }
	/// ```
	pub fn cut_err<I, O, E: ParserError<I>, F>(mut parser: F) -> impl Parser<I, O, E>
	where
	I: Stream,
	F: Parser<I, O, E>,
	{
	trace("cut_err", move \|input: &mut I\| {
	parser.parse_next(input).map_err(\|e\| e.cut())
	})
	}

	/// Transforms an [`ErrMode::Cut`] (unrecoverable) to [`ErrMode::Backtrack`] (recoverable)
	///
	/// This attempts the parse, allowing other parsers to be tried on failure, like with
	/// [`winnow::combinator::alt`][crate::combinator::alt].
	pub fn backtrack_err<I, O, E: ParserError<I>, F>(mut parser: F) -> impl Parser<I, O, E>
	where
	I: Stream,
	F: Parser<I, O, E>,
	{
	trace("backtrack_err", move \|input: &mut I\| {
	parser.parse_next(input).map_err(\|e\| e.backtrack())
	})
	}

	/// A placeholder for a not-yet-implemented [`Parser`]
	///
	/// This is analogous to the [`todo!`] macro and helps with prototyping.
	///
	/// # Panic
	///
	/// This will panic when parsing
	///
	/// # Example
	///
	/// ```rust
	/// # use winnow::prelude::*;
	/// # use winnow::combinator::todo;
	///
	/// fn parser(input: &mut &str) -> PResult<u64> {
	/// todo(input)
	/// }
	/// ```
	#[track_caller]
	pub fn todo<I, O, E>(input: &mut I) -> PResult<O, E>
	where
	I: Stream,
	{
	#![allow(clippy::todo)]
	trace("todo", move \|_input: &mut I\| todo!("unimplemented parse")).parse_next(input)
	}

	/// Repeats the embedded parser, lazily returning the results
	///
	/// Call the iterator's [`ParserIterator::finish`] method to get the remaining input if successful,
	/// or the error value if we encountered an error.
	///
	/// On [`ErrMode::Backtrack`], iteration will stop. To instead chain an error up, see [`cut_err`].
	///
	/// # Example
	///
	/// ```rust
	/// use winnow::{combinator::iterator, IResult, token::tag, ascii::alpha1, combinator::terminated};
	/// use std::collections::HashMap;
	///
	/// let data = "abc\|defg\|hijkl\|mnopqr\|123";
	/// let mut it = iterator(data, terminated(alpha1, "\|"));
	///
	/// let parsed = it.map(\|v\| (v, v.len())).collect::<HashMap<_,_>>();
	/// let res: IResult<_,_> = it.finish();
	///
	/// assert_eq!(parsed, [("abc", 3usize), ("defg", 4), ("hijkl", 5), ("mnopqr", 6)].iter().cloned().collect());
	/// assert_eq!(res, Ok(("123", ())));
	/// ```
	pub fn iterator<I, O, E, F>(input: I, parser: F) -> ParserIterator<F, I, O, E>
	where
	F: Parser<I, O, E>,
	I: Stream,
	E: ParserError<I>,
	{
	ParserIterator {
	parser,
	input,
	state: Some(State::Running),
	o: Default::default(),
	}
	}

	/// Main structure associated to [`iterator`].
	pub struct ParserIterator<F, I, O, E>
	where
	F: Parser<I, O, E>,
	I: Stream,
	{
	parser: F,
	input: I,
	state: Option<State<E>>,
	o: core::marker::PhantomData<O>,
	}

	impl<F, I, O, E> ParserIterator<F, I, O, E>
	where
	F: Parser<I, O, E>,
	I: Stream,
	{
	/// Returns the remaining input if parsing was successful, or the error if we encountered an error.
	pub fn finish(mut self) -> PResult<(I, ()), E> {
	match self.state.take().unwrap() {
	State::Running \| State::Done => Ok((self.input, ())),
	State::Failure(e) => Err(ErrMode::Cut(e)),
	State::Incomplete(i) => Err(ErrMode::Incomplete(i)),
	}
	}
	}

	impl<'a, F, I, O, E> core::iter::Iterator for &'a mut ParserIterator<F, I, O, E>
	where
	F: Parser<I, O, E>,
	I: Stream,
	{
	type Item = O;

	fn next(&mut self) -> Option<Self::Item> {
	if let State::Running = self.state.take().unwrap() {
	let start = self.input.checkpoint();

	match self.parser.parse_next(&mut self.input) {
	Ok(o) => {
	self.state = Some(State::Running);
	Some(o)
	}
	Err(ErrMode::Backtrack(_)) => {
	self.input.reset(start);
	self.state = Some(State::Done);
	None
	}
	Err(ErrMode::Cut(e)) => {
	self.state = Some(State::Failure(e));
	None
	}
	Err(ErrMode::Incomplete(i)) => {
	self.state = Some(State::Incomplete(i));
	None
	}
	}
	} else {
	None
	}
	}
	}

	enum State<E> {
	Running,
	Done,
	Failure(E),
	Incomplete(Needed),
	}

	/// Succeed, consuming no input
	///
	/// For example, it can be used as the last alternative in `alt` to
	/// specify the default case.
	///
	/// Useful with:
	/// - [`Parser::value`]
	/// - [`Parser::default_value`]
	/// - [`Parser::map`]
	///
	/// Note: This never advances the [`Stream`]
	///
	/// # Example
	///
	/// ```rust
	/// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError};
	/// # use winnow::prelude::*;
	/// use winnow::combinator::alt;
	/// use winnow::combinator::empty;
	///
	/// fn sign(input: &str) -> IResult<&str, isize> {
	/// alt((
	/// '-'.value(-1),
	/// '+'.value(1),
	/// empty.value(1)
	/// )).parse_peek(input)
	/// }
	/// assert_eq!(sign("+10"), Ok(("10", 1)));
	/// assert_eq!(sign("-10"), Ok(("10", -1)));
	/// assert_eq!(sign("10"), Ok(("10", 1)));
	/// ```
	#[doc(alias = "value")]
	#[doc(alias = "success")]
	pub fn empty<I: Stream, E: ParserError<I>>(_input: &mut I) -> PResult<(), E> {
	Ok(())
	}

	/// Deprecated, replaced with [`empty`] + [`Parser::value`]
	#[deprecated(since = "0.5.35", note = "Replaced with empty.value(...)`")]
	pub fn success<I: Stream, O: Clone, E: ParserError<I>>(val: O) -> impl Parser<I, O, E> {
	trace("success", move \|_input: &mut I\| Ok(val.clone()))
	}

	/// A parser which always fails.
	///
	/// For example, it can be used as the last alternative in `alt` to
	/// control the error message given.
	///
	/// # Example
	///
	/// ```rust
	/// # use winnow::{error::ErrMode, error::ErrorKind, error::InputError, IResult};
	/// # use winnow::prelude::*;
	/// use winnow::combinator::fail;
	///
	/// let s = "string";
	/// assert_eq!(fail::<_, &str, _>.parse_peek(s), Err(ErrMode::Backtrack(InputError::new(s, ErrorKind::Fail))));
	/// ```
	#[doc(alias = "unexpected")]
	pub fn fail<I: Stream, O, E: ParserError<I>>(i: &mut I) -> PResult<O, E> {
	trace("fail", \|i: &mut I\| {
	Err(ErrMode::from_error_kind(i, ErrorKind::Fail))
	})
	.parse_next(i)
	}