Method expect

perro_source/core/perro_animation/src/anim_tree.rs:479–485

(&mut self, token: Token<'a>)

    }

    fn expect(&mut self, token: Token<'a>) -> Result<(), String> {
        if self.current != token {
            return Err(format!("expected {token:?}, got {:?}", self.current));
        }
        self.advance();
        Ok(())
    }

    fn expect_ident(&mut self) -> Result<String, String> {
        match std::mem::replace(&mut self.current, Token::Eof) {