title: Lisp - Convert symbol to string only if not already a string
body: <p>Is there a way to convert symbol to string only if it is not already a string in lisp?</p>
  
  <p>It should work like this:</p>
  
  <p>(only-if-convertion 'ABC) => "ABC"</p>
  
  <p>(only-if-convertion "ABC") => "ABC"</p>