rustmax::nom::combinator

Function peek

Source 
pub fn peek<I, F>(
    parser: F,
) -> impl Parser<I, Output = <F as Parser<I>>::Output, Error = <F as Parser<I>>::Error>
where
    I: Clone,
    F: Parser<I>,
Expand description

Tries to apply its parser without consuming the input.

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

let mut parser = peek(alpha1);

assert_eq!(parser.parse("abcd;"), Ok(("abcd;", "abcd")));
assert_eq!(parser.parse("123;"), Err(Err::Error(("123;", ErrorKind::Alpha))));