Forgetting compile time stuff

[Helmut Eller]

After compiling a file with content:

(eval-when (:compile-toplevel)
  (defun foo () (format t "foo~%")))

with (compile-file "foo.lisp") the function foo is defined
after compile-file returns.

Is there a knob to change that so that foo is defined only while
compiling?

Helmut