并行迭代

在 LOOP 中允许多个 FOR 条款。当第一个子句结束时，循环结束：

(loop for a in '(1 2 3 4 5)
      for b in '(a b c)
      collect (list a b))
;; Evaluates to: ((1 a) (2 b) (3 c))

确定循环是否应该继续的其他子句可以组合使用：

(loop for a in '(1 2 3 4 5 6 7)
      while (< a 4)
      collect a)
;; Evaluates to: (1 2 3)

(loop for a in '(1 2 3 4 5 6 7)
      while (< a 4)
      repeat 1
      collect a)
;; Evaluates to: (1)

确定哪个列表更长，一旦知道答案就切断迭代：

(defun longerp (list-1 list-2)
    (loop for cdr1 on list-1
          for cdr2 on list-2
          if (null cdr1) return nil
          else if (null cdr2) return t
          finally (return nil)))

编号列表的元素：

(loop for item in '(a b c d e f g)
      for x from 1
      collect (cons x item))
;; Returns ((1 . a) (2 . b) (3 . c) (4 . d) (5 . e) (6 . f) (7 . g))

确保列表中的所有数字均匀，但仅适用于前 100 个项目：

(assert
   (loop for number in list
         repeat 100
         always (evenp number)))