When pure function lie

https://coredumped.dev/2021/04/07/when-pure-function-lie/ · Here is a simple question. Given the lisp function below (and that the function is not advised) what will the output be of (foo)? (defun foo () "foo") Seems pretty simple right? How could the answer be anything other then "foo"? It is just returning a constant string. Or is it? The real answer to this question is… We have no idea. It can could be any string of length 3.