第拾伍章學習 Lisp 3rd Edition, Winston & Horn

LEXICAL VARIABLES GENERATORS AND ENCAPSULATION
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LETS PRODUCE NESTED FENCES

(defun both-ends-with-let (whole-list)
  (let ((leading (first whole-list))             ;Bind LEADING.
        (trailing (first (last whole-list))))    ;Bind TRAILING.
    (list leading trailing)))

(defun both-ends-with-funny-let (whole-list)
  (let (leading trailing)                        ;Bind both to NIL.
    (setf leading (first whole-list)             ;Assign new value.
    (setf trailing (first (last whole-list)))    ;Assign new value.
    (list leading trailing)))                    ;Combine.
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NESTED FENCES PROVIDE VARIABLE VALUES