Function snarkvm_circuit::environment::prelude::opt

pub fn opt<I, O, E, F>(f: F) -> impl FnMut(I)where
    I: Clone,
    E: ParseError<I>,
    F: Parser<I, O, E>,

Optional parser, will return None on [Err::Error].

To chain an error up, see [cut].

use nom::combinator::opt;
use nom::character::complete::alpha1;

fn parser(i: &str) -> IResult<&str, Option<&str>> {
  opt(alpha1)(i)
}

assert_eq!(parser("abcd;"), Ok((";", Some("abcd"))));
assert_eq!(parser("123;"), Ok(("123;", None)));