/// if the expr is a non null literal string, returns the string value
if the expr is a non null literal string, returns the string value
if the expr is a non null literal string returns the string value
fn as_str_lit(expr: &Expr) -> Option<&str> {
    if let Expr::Literal(ScalarValue::Utf8(Some(name))) = &expr {
        Some(name.as_str())
    } else {
        None
    }
}
fn as_str_lit ( expr : & Expr ) -> Option < & str > { if let Expr :: Literal ( ScalarValue :: Utf8 ( Some ( name ) ) ) = & expr { Some ( name . as_str ( ) ) } else { None } }
if the expr is a non null literal string, returns the string value
if the expr is a non null literal string returns the string value
expr
&Expr