Enum Lookahead

pub enum Lookahead {
    Positive,
    Negative,
    None,
}

The current lookahead status of a ParserState.

Variants

Positive

The positive predicate, written as an ampersand &, attempts to match its inner expression. If the inner expression succeeds, parsing continues, but at the same position as the predicate — &foo ~ bar is thus a kind of “AND” statement: “the input string must match foo AND bar”. If the inner expression fails, the whole expression fails too.

Negative

The negative predicate, written as an exclamation mark !, attempts to match its inner expression. If the inner expression fails, the predicate succeeds and parsing continues at the same position as the predicate. If the inner expression succeeds, the predicate fails — !foo ~ bar is thus a kind of “NOT” statement: “the input string must match bar but NOT foo”.

None

No lookahead (i.e. it will consume input).

Trait Implementations

impl Clone for Lookahead

fn clone(&self) -> Lookahead

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Lookahead

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for Lookahead

fn eq(&self, other: &Lookahead) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for Lookahead

impl Eq for Lookahead

impl StructuralPartialEq for Lookahead