Homework 2 (Due Monday 1/31/11 at 10:00 am)

Submit via OWLSPACE in a single (.ss or .rkt) file that is runnable in DrScheme (so all expository answers must be enclosed in comment blocks or commented out using semi-colons.s into one file and submit this one compressed file. We did not deduct any points for using the wrong format on HW01 but we will deduct points for this error on this assignment. Begin each problem with a comment line containing the number of the problem.

The type "natural number" (N) in this assignment means the natural-number type defined in the text in Section 11.1. Your file should include a data definition for N. Unless the problem statement stipulates otherwise, the only built-in operations you may use with values of this type or variants (such as natural>=1) are the constructors, accessors, and recognizers for the type and the equal? (or =}) operation. For N, the constructor is add1 ; the accessor is sub1, and the recognizers are zero? and positive?.
For variants, the constructor is typically add1 (unless the variant consists of multiples of m > 1 [such as the even numbers]), the accessor is typically sub1, and the recognizers are typically (equal? ... k), where k is the base number, and (> ... k).

Problems from the book (HTDP) with some customization

  • 11.2.4 (20 pts.)
    • Copy the definition of deep-list from the text. Be sure to provide your own function template for deep-list and to write template instantiations for depth and make-deep.
  • 11.4.7 (20 pts.)
    • Include a data definition (following the text) of natural>=1. In addition to the constructors, accessors, recognizers, and equal?, you may use the library functions remainder and * . Hint: define an auxiliary function is-divisible-by of two inputs p and q (using the remainder library function) that determines if p is divisible by q (i.e., p/q is a whole number).
    • Note that the problem as stated in the book has TWO parts; the second, writing prime? is easy after doing the first. Do not worry about optimizing the search for a divisor for n by bounding the search to numbers less or equal to (integer-sqrt n); for simplicity, the integer-sqrt and sqrt library functions are forbidden in this exercise.
  • 12.2.2 (20 pts.)
  • 12.4.2 (30 pts.)
    • Do this problem followed by developing the function arrangements that returns a list containing all of the arrangements (permutations) of the input word. This function is described in detail in the text and the code for it is given to you in the statement of problem 12.4.1. You are expected to present this answer in your program file as if you developed it, including supporting test data.
    • The Hint for this problem should include the following:
      • Your program must distinguish between the types word and list-of-word and process them separately. The data-driven approach to program design preached in this course naturally leads to this distinction.
      • The behavior of the function insert-everywhere/in-all-words is more easily understood given the following examples:
        (insert-everywhere/in-all-words 'd (list (list 'e 'r))) = (list (list 'd 'e 'r) (list 'e 'd 'r) (list 'e 'r 'd))
        (insert-everywhere/in-all-words 'd (list (list 'e 'r) (list 'r 'e))) =
          (list (list 'd 'e 'r) (list 'e 'd 'r) (list 'e 'r 'd) (list 'd 'r 'e) (list 'r 'd 'e) (list 'r 'e 'd))
      • You will need to write a help function insert-everywhere where (insert-everywhere s w) inserts the letter s in each possible position in the word w, including before and after all letters of w. Note the difference in the type contracts for insert-everywhere and insert-everywhere/in-all-words.
    • Notes: the function arrangements computes all of the permutations of the input word. Permutation is an important concept in basic probability theory. For some reason, the authors of the book chose to avoid using the relevant mathematical terminology. This problem includes writing the arrangements function because it is cool and developing insert-everywhere/in-all-words is the bulk of the work involved in developing arrangements .
  • 13.0.5 (part 4 only) (5 pts.)
  • 13.0.8 (part 2 only) (5 pts.)
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