There are poorly designed parser rules but the namespace operator is not due to that. It's due to the fact that a single PHP file will be compiled to byte code without knowing what the symbols represent until runtime. The separate operator is needed because names are resolved before execution begins and before the symbols are known.

> Also, magically, I can't use empty(functionResult()); but I can say $result = functionResult(); empty($result);

Empty is identical to the not (!) operator except that empty() can operate on undefined variables, undefinted array keys, or undefined properties. empty(functionResult()) doesn't make any sense because functionResult() can never be an undefined variable. You just use !functionResult().