1.1.2 Differences between LOOP and DO

1.1.2.3 Example 3

;;; These functions sum the elements of an array. Since the Loop 
;;; Facility supports iteration over arrays, the code is simple.
(defun sum-array-loop (array)               ; Use Loop Facility 
  (loop for a being the elements of array   ; constructs.
        sum a))

(defun sum-array-do (array)                 ; Use the DO macro.
  (do ((index 0 (1+ index))
        (sum 0))
      ((= index (length array)) sum)
    (incf sum (aref array index))))

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