Function bparse::not

pub const fn not<P: Pattern>(pattern: P) -> Not<P>

Expresses pattern negation

Returns a new pattern that will match only if pattern does not match

Note: This is a peek-like operation. It will always return Some((&[], _)) (i.e. an empty slice) in the successful case. It does not advance Parser. It is useful for “negative lookahead”

Example

Say you want to match a string of multiple ’a’s and ’b’s, except the string must not end in a ‘b’:

use bparse::{Pattern, not, end};

let input1 = b"aabaaaa";
let input2 = b"aaaab";

// a pattern of either a's or b's that do not occur at the input
let pattern = "a".or("b".and(not(end))).repeats(0..);

assert_eq!(b"aabaaaa", pattern.test(input1).unwrap().0);
assert_eq!(b"aaaa", pattern.test(input2).unwrap().0);

Example

use bparse::{Pattern, not};

let input = b"b";
let pattern = not("a");

assert!(matches!(pattern.test(input), Some((&[], _))));