Function winnow::combinator::fold_repeat

pub fn fold_repeat<I, O, E, F, G, H, R>(
    range: impl Into<Range>,
    f: F,
    init: H,
    g: G,
) -> impl Parser<I, R, E>
where
    I: Stream,
    F: Parser<I, O, E>,
    G: FnMut(R, O) -> R,
    H: FnMut() -> R,
    E: ParserError<I>,

Repeats the embedded parser m..=n times, calling g to gather the results

This stops before n when the parser returns ErrMode::Backtrack. To instead chain an error up, see cut_err.

Arguments

• m The minimum number of iterations.
• n The maximum number of iterations.
• f The parser to apply.
• init A function returning the initial value.
• g The function that combines a result of f with the current accumulator.

Warning: If the parser passed to fold_repeat accepts empty inputs (like alpha0 or digit0), fold_repeat will return an error, to prevent going into an infinite loop.

Example

Zero or more repetitions:

use winnow::combinator::fold_repeat;
use winnow::token::tag;

fn parser(s: &str) -> IResult<&str, Vec<&str>> {
  fold_repeat(
    0..,
    "abc",
    Vec::new,
    |mut acc: Vec<_>, item| {
      acc.push(item);
      acc
    }
  ).parse_peek(s)
}

assert_eq!(parser("abcabc"), Ok(("", vec!["abc", "abc"])));
assert_eq!(parser("abc123"), Ok(("123", vec!["abc"])));
assert_eq!(parser("123123"), Ok(("123123", vec![])));
assert_eq!(parser(""), Ok(("", vec![])));

One or more repetitions:

use winnow::combinator::fold_repeat;
use winnow::token::tag;

fn parser(s: &str) -> IResult<&str, Vec<&str>> {
  fold_repeat(
    1..,
    "abc",
    Vec::new,
    |mut acc: Vec<_>, item| {
      acc.push(item);
      acc
    }
  ).parse_peek(s)
}

assert_eq!(parser("abcabc"), Ok(("", vec!["abc", "abc"])));
assert_eq!(parser("abc123"), Ok(("123", vec!["abc"])));
assert_eq!(parser("123123"), Err(ErrMode::Backtrack(InputError::new("123123", ErrorKind::Many))));
assert_eq!(parser(""), Err(ErrMode::Backtrack(InputError::new("", ErrorKind::Many))));

Arbitrary number of repetitions:

use winnow::combinator::fold_repeat;
use winnow::token::tag;

fn parser(s: &str) -> IResult<&str, Vec<&str>> {
  fold_repeat(
    0..=2,
    "abc",
    Vec::new,
    |mut acc: Vec<_>, item| {
      acc.push(item);
      acc
    }
  ).parse_peek(s)
}

assert_eq!(parser("abcabc"), Ok(("", vec!["abc", "abc"])));
assert_eq!(parser("abc123"), Ok(("123", vec!["abc"])));
assert_eq!(parser("123123"), Ok(("123123", vec![])));
assert_eq!(parser(""), Ok(("", vec![])));
assert_eq!(parser("abcabcabc"), Ok(("abc", vec!["abc", "abc"])));