MCS-177 Homework 7, Fall 2005

Due: November 28, 2005

• Exercise 7.x2: Suppose that the reverse-onto procedure, defined internally to reverse on pages 181-182, were instead defined separately. Now consider the following procedure definition:

  (define mystery
    (lambda (list1 list2)
      (reverse-onto (reverse list1)
                    list2)))
  

  1. Describe clearly what the mystery procedure does, and how you know that it does that.

  2. Write a procedure that has the same effect as the mystery procedure, but which generates a linearly recursive process and calls only on itself and the built-in procedures cons, car, cdr, and null?.

• Do exercise 7.21 on page 187.

• Do exercise 7.49 on page 208. Your procedure should work even when given an empty list. To understand what the correct answer is for an empty list, consider this: all elements of a list are postive if there are none that are not positive. In addition to providing your procedure definition, you should explain whether it generates an interative or recursive process.