Method expect

std/re/src/main/parser.rs:41–44

(&mut self, c: char)

    fn err(&self, msg: &'static str) -> ParseError { ParseError { msg, pos: self.pos } }

    fn expect(&mut self, c: char) -> Result<(), ParseError> {
        if self.peek() == Some(c) { self.bump(); Ok(()) }
        else { Err(self.err("missing closing parenthesis")) }
    }

    /* Lowest precedence, branches split on the pipe. */
    fn alternation(&mut self) -> Result<Node, ParseError> {