{"ast_node_type":"variable","tokens":[{"end":50,"kind":"keyword","start":0,"text":"if"}]}
    if let Some(expected_token) = expected_token {
fn parse_failure_msg(tok: &Token, expected_token: Option<&Token>) -> Cow<'static, str> {
        Cow::from(format!("expected {}, found {}", token_descr(expected_token), token_descr(tok)))