Expand description
attempt(p)
behaves as p
except it always acts as p
peeked instead of committed on its
parse.
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());