P22 - Create a list containing all integers within a given range

lisp

;;; Function that generates a list containing all integers in ;;;
;;; a given interval. If the beginning is less than the end, it generates ;;;
;;; a descending list ;;;

(defun range (ini end)
    (if (> ini fim)
        ;; if the list is from a larger number to a smaller ;;
        (if (eql ini fim)
            (cons fim nil)
            (cons ini (range (- ini 1) end))
        
        ;; if the list is from a smaller number to a larger ;;
        (if (eql ini fim)
            (cons fim nil)
            (cons ini (range (+ ini 1) end)))