Function cond

pub fn cond<Input, Output, Error, ParseNext>(
    cond: bool,
    parser: ParseNext,
) -> impl Parser<Input, Option<Output>, Error>
where
    Input: Stream,
    ParseNext: Parser<Input, Output, Error>,
    Error: ParserError<Input>,

Calls the parser if the condition is met.

Example

use winnow::combinator::cond;
use winnow::ascii::alpha1;

fn parser<'i>(i: &mut &'i str) -> ModalResult<Option<&'i str>> {
  let prefix = opt("-").parse_next(i)?;
  let condition = prefix.is_some();
  cond(condition, alpha1).parse_next(i)
}

assert_eq!(parser.parse_peek("-abcd;"), Ok((";", Some("abcd"))));
assert_eq!(parser.parse_peek("abcd;"), Ok(("abcd;", None)));
assert!(parser.parse_peek("-123;").is_err());
assert_eq!(parser.parse_peek("123;"), Ok(("123;", None)));