Interactive option for command application

[Heime <heimeborgia@protonmail.com>]

What would be a convenient way for the user to select whether a change is to be made to
a buffer or to a frame?  Currently the user has to enter "yes" or "no' to the question
to set the boolean flag.  Generally, users would perform the change only upon the buffer,
and only occasionally upon the frame.

(defun monfont (face-family face-height okvir)

  (interactive

    (list

      (let ( (cseq '("Wargames" "URW Chancery L" "Century Schoolbook L")) )

        (completing-read " Family Name: " cseq nil t "Century Schoolbook L"))


      (let ( (hseq '("260" "220" "180")) )

        (completing-read " Face Height: " hseq nil t "180")) 


      (yes-or-no-p "Apply to Frame ? ") )) 

  (if okvir
      (do-this)
    (do-that)) )