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Recursive Functions, Part I


During this activity, students should be able to:

This activity helps students develop the following skills, values and attitudes: ability to analyze and synthesize, capacity for identifying and solving problems, and efficient use of computer systems.

Activity Description

Individually, solve the following set of programming exercises using Clojure. Place all your functions in a name space called recursion. All problems should be solved using explicit recursion or the recur and loop special forms.

  1. The function my-count returns the number of elements contained in its input list. Do not use the predefined count function. Unit tests:
    (deftest test-my-count
      (is (= 0 (my-count ())))
      (is (= 1 (my-count '(a))))
      (is (= 3 (my-count '(a b c)))))
  2. The function add-list returns the sum of all the elements of its input list, or 0 if its empty. Assume that all the elements in the input list are numbers. Unit tests:
    (deftest test-add-list
      (is (= 0 (add-list ())))
      (is (= 10 (add-list '(2 4 1 3))))
      (is (= 55 (add-list '(1 2 3 4 5 6 7 8 9 10)))))
  3. The function member? takes two arguments, any data x and a list lst. Returns true if x is contained inside the list lst, false otherwise. Unit tests:
    (deftest test-member?
      (is (not (member? 'a ())))
      (is (member? 'a '(a b c)))
      (is (member? 'a '(c b a b c)))
      (is (not (member? 'x '(a b c)))))
  4. The function list-of-symbols? takes a list lst as its argument. It returns true if all the elements (possibly zero) contained in lst are symbols, or false otherwise. Unit tests.
    (deftest test-list-of-symbols?
      (is (list-of-symbols? ()))
      (is (list-of-symbols? '(a)))
      (is (list-of-symbols? '(a b c d e)))
      (is (not (list-of-symbols? '(a b c d 42 e))))
      (is (not (list-of-symbols? '(42 a b c)))))
  5. The function my-last returns the last element of its input list, or nil of its empty. Do not use the predefined last function. Unit test:
    (deftest test-my-last
      (is (nil? (my-last ())))
      (is (= 'x (my-last '(x))))
      (is (= 'c (my-last '(a b c)))))
  6. The function conj-end takes two arguments, a list lst and any data x. Returns a list composed by the same elements of lst but with x at the end. Unit tests:
    (deftest test-conj-end
      (is (= '(b c d a) (conj-end '(b c d) 'a)))
      (is (= '(a) (conj-end () 'a ))))
  7. The function my-butlast returns a list with the same elements as its input list but excluding the last element, or nil of its empty. Do not use the predefined butlast function. Unit tests:
    (deftest test-my-butlast
      (is (nil? (my-butlast ())))
      (is (= () (my-butlast '(x))))
      (is (= '(a b) (my-butlast '(a b c)))))
  8. The function my-concat returns the resulting list of appending the two lists it takes as input. Do not use the predefined concat function. Unit tests:
    (deftest test-my-concat
      (is (= '(a b c) (my-concat '(a b c) ())))
      (is (= '(1 2 3) (my-concat () '(1 2 3))))
      (is (= '(a b c 1 2 3) (my-concat '(a b c) '(1 2 3)))))
  9. The function my-reverse takes a list as an argument. It returns another list with the same elements as the input list, but in reverse order. Do not use the predefined reverse function. Unit test:
    (deftest test-my-reverse
      (is (= () (my-reverse ())))
      (is (= '(c b a) (my-reverse '(a b c))))
      (is (= '(3 (b c d) a) (my-reverse '(a (b c d) 3)))))
  10. The function deep-reverse takes a list as its input. It returns a list with the same elements as its input but in reverse order. If there are any nested lists, these too should be reversed. Unit tests:
    (deftest test-deep-reverse
      (is (= () (deep-reverse ())))
      (is (= '(3 (d c b) a) (deep-reverse '(a (b c d) 3))))
      (is (= '(((6 5) 4) 3 (2 1)) (deep-reverse '((1 2) 3 (4 (5 6)))))))

Source of many of these problems: Ninety-Nine Lisp Problems


Using the Online Assignment Delivery System (SETA), deliver a single file called recursion.clj containing your solutions and the unit tests. No assignments will be accepted through e-mail or any other means.

IMPORTANT: The program source file must include at the top the author's personal information (name and student id) within comments. For example:

;;; ITESM CEM, August 24, 2012.
;;; Clojure Source File
;;; Activity: Recursive Functions, Part I
;;; Author: Steve Rogers, 1166611

    . (The rest of the program goes here)

Due date: Friday, August 24.


This activity will be evaluated using the following criteria:

-10 The program doesn't contain within comments the author's personal information.
10 The program contains syntax errors.
DA The program was plagiarized.
10-100 Depending on the amount of exercises that were solved correctly.