Function combine::attempt

pub fn attempt<P>(p: P) -> Try<P>where
    P: Parser,

attempt(p) behaves as p except it acts as if the parser hadn’t consumed any input if p fails after consuming input. (alias for try)

let mut p = attempt(string("let"))
    .or(string("lex"));
let result = p.parse("lex").map(|x| x.0);
assert_eq!(result, Ok("lex"));
let result = p.parse("aet").map(|x| x.0);
assert!(result.is_err());

attempt is an alias for try. It was added because try is now a keyword in Rust 2018.