(defun digits (n) (map 'vector #'digit-char-p (princ-to-string n)))
(defun num (digits)
  (let ((num 0)
        (wdigits (reverse digits)))
    (loop for digit across digits do
         (incf num digit)
         (setf num (* num 10)))
    (/ num 10)))

(defun prime-p (num)
  (if (< num 3)
      (equal num 2)
      (not
       (loop for i from 2 to (floor (sqrt num)) do
            (when (zerop (mod num i))
              (return t))))))

(defun rtrunc (number)
  (labels ((work (dgts)
             (when (prime-p (num dgts))
               (if (equal 1 (length dgts))
                   t
                   (rtrnc (subseq dgts 0 (1- (length dgts))))))))
    (work (digits number))))

(defmacro ltrunc (number)
  (labels ((work (dgts)
               (when (prime-p (num dgts))
                 (if (equal 1 (length dgts))
                     t
                     (ltrnc (subseq dgts 1))))))
    (work (digits number))))


(defun problem-37 ()
  (let ((count 0)
        (current 8)
        (nums nil))
    (loop while (< count 11) do
         (when (and (ltrunc current) (rtrunc current))
           (print current)
           (push current nums)
           (incf count))
         (incf current))
    (reduce #'+ nums)))