expand-intervals/integers

;;;; function (-> don't know if this is already existing in opusmodus)

(defun expand-intervals/integers (seq &key (type 'add) (value 1))
  (cond ((equal type 'add)
         (loop for i in seq
           when (> i 0)
           collect (+ i value)
           when (< i 0)
           collect (- i value)
           when (= i 0)
           collect i))
        ((equal type 'multiply)
         (loop for i in seq
           collect (* i value)))
        ((equal type 'expt)
         (loop for i in seq
           when (>= i 0)
           collect (expt i value)
           else collect (* (expt i value) -1)))
        ((equal type 'fibonacci)
         (loop for i in seq
           when (>= i 0)
           collect (+ i (fibonacci i))
           else collect (- i (fibonacci (abs i)))))))
         
;;; examples 
             
(expand-intervals/integers '(0 -1 1 -2 2 -3 3)
                           :type 'add
                           :value 2)

(expand-intervals/integers '(0 -1 1 -2 2 -3 3)
                           :type 'multiply
                           :value 2)

(expand-intervals/integers '(0 -1 1 -2 2 -3 3)
                           :type 'expt
                           :value 2)
        
(expand-intervals/integers '(0 -1 1 -2 2 -3 3 -4 4 -5 5)
                           :type 'fibonacci)