Define a procedure make-prev that can be used to create the procedure prev described in part a. make-prev should take as an argument the value that should be returned by the first call to prev. That is, if we (define prev (make-prev ’first-call )) prev should behave as shown above.（use lisp piease）

以下是用 Lisp 实现的 `make-prev` 过程，它可以用来创建 `prev` 过程：

(defun make-prev (init-value)
  (let ((prev-value init-value))
    (lambda ()
      (let ((current-value prev-value))
        (setf prev-value (read))
        current-value))))

这个过程接受一个初始值 `init-value` 作为参数，并返回一个新过程。当调用这个新过程时，它会先返回初始化时传入的值，然后每次调用时返回上一次传入的参数。具体可以参考题目中给出的 `prev` 过程的行为。

例如，我们可以使用以下代码定义 `prev` 过程：

(defvar prev (make-prev 'first-call))

现在，我们可以通过调用 `prev` 过程来获取上一个传入的值，例如：

(funcall prev) ; => FIRST-CALL
(funcall prev) ; => NIL
(funcall prev) ; => HELLO
(funcall prev) ; => WORLD

相关问题

Define a procedure make-prev that can be used to create the procedure prev described in part a. make-prev should take as an argument the value that should be returned by the first call to prev. That is, if we (define prev (make-prev ’first-call )) prev should behave as shown above.

Here is a possible implementation of the `make-prev` procedure in Scheme:

(define (make-prev initial-value)
  (let ((prev-value initial-value))
    (lambda (x)
      (let ((result prev-value))
        (set! prev-value x)
        result))))

The `make-prev` procedure takes one argument `initial-value`, which is the value that should be returned by the first call to the `prev` procedure. The procedure returns a new anonymous procedure that behaves like the `prev` procedure described in the previous question. The `prev-value` variable is initialized to `initial-value`, and the anonymous procedure returned by `make-prev` takes one argument `x`. On the first call to the anonymous procedure, it returns `prev-value`, which is the initial value of `prev-value`. On subsequent calls, it returns the previous value of `x` that was passed to it, which is stored in `prev-value`, and updates `prev-value` to the current value of `x`. Here are some examples of using `make-prev`:

(define prev (make-prev 'first-call))
(prev 'a) ;=> first-call
(prev 3) ;=> a
(prev (+ 1 5)) ;=> 3

Note that the `make-prev` procedure creates a new `prev` procedure each time it is called with a different initial value. This allows you to create multiple `prev` procedures with different initial values if needed.