From cassidoo's November 20, 2023 newsletter

between-nums.lisp

(defun range (x y)
  (let ((start (min x y)) (end (max x y)))
    (loop for i from start to end
          collect i)))

(defun primep (num)
  (cond
    ((<= num 1) nil)
    ((= num 2) t)
    (t
     (let ((divisor-count 0))
       (loop for i from 2 to (isqrt num)
             until (= 2 divisor-count)
             do (when (zerop (rem num i))
                  (incf divisor-count))
             finally (return (zerop divisor-count)))))))

(defun between-nums (start end action)
  (let ((act (if (equal action "even")   #'evenp
             (if (equal action "odd")    #'oddp
             (if (equal action "prime")  #'primep
                (return-from between-nums nil))))))
    (remove-if-not act
      (range start end))))