ANSI Common Lisp   6 Iteration   6.1 The LOOP Facility

6.1.8 Examples of Miscellaneous Loop Features

 (let ((i 0))                     ; no loop keywords are used
    (loop (incf i) (if (= i 3) (return i))))  3
 (let ((i 0)(j 0))
    (tagbody
      (loop (incf j 3) (incf i) (if (= i 3) (go exit)))
      exit)
    j)  9

In the following example, the variable x is stepped before y is stepped; thus, the value of y reflects the updated value of x:

 (loop for x from 1 to 10 
       for y = nil then x 
       collect (list x y))
 ((1 NIL) (2 2) (3 3) (4 4) (5 5) (6 6) (7 7) (8 8) (9 9) (10 10))

In this example, x and y are stepped in parallel:

 (loop for x from 1 to 10 
       and y = nil then x 
       collect (list x y))
 ((1 NIL) (2 1) (3 2) (4 3) (5 4) (6 5) (7 6) (8 7) (9 8) (10 9))

6.1.8.1  Examples of clause grouping