The Yin Yang Puzzle

David Madore posted the following puzzle to comp.lang.scheme in late 1999:

    (let* ((yin ((lambda (foo) (newline) foo)
                 (call/cc (lambda (bar) bar))))
           (yang ((lambda (foo) (write-char #\*) foo)
                  (call/cc (lambda (bar) bar)))))
      (yin yang))

What does the program print - and why?

Spoiler: https://stackoverflow.com/q/2694679/23567