calculator.lisp

(defun prompt-read (prompt)
  (format *query-io* "~a:" prompt)
  (force-output *query-io*)
  (read-line *query-io*))

(defun make-calc-prompt ()
  (defparameter  num1 (parse-integer (prompt-read "First number")))
  (defparameter op (prompt-read "Operator (+-/*)"))
  (defparameter num2 (parse-integer (prompt-read "Second number")))
  (cond
    ((string= op "+") (return-from make-calc-prompt (+ num1 num2)))
    ((string= op "-") (return-from make-calc-prompt (- num1 num2)))
    ((string= op "*") (return-from make-calc-prompt (* num1 num2)))
    ((string= op "/") (return-from make-calc-prompt (/ num1 num2)))))