CSC 160 HW9

Assigned due 1 May, due 10 May

Also turn in a log of how many errors of different kinds you encountered in the assignment, with brief comments describing each one ("mismatched parentheses" is self-explanatory, but more complex errors might need more description).

This assignment is to be done in pairs, as before.

• Define a struct to represent a person, with a name and an age. Develop a function oldest, which takes a non-empty list of persons, and returns the oldest person.
• Do exercises 12.2.1 and 12.2.2. (Notice the sentence in the textbook, "The function must take advantage of the fact that the list is sorted"! The function provided in the textbook is already correct; yours should be correct but more efficient.)
• Do exercise 12.3.1.
• Do (but don't turn in) exercise 12.4.1.
  Do exercise 12.4.2, which depends on problem 12.4.1 above. (The book develops arrangements, using the auxiliary function insert-everywhere/in-all-words, which you are to write. It'll probably require two more auxiliary functions of its own. Be careful with types: a list of symbols is not the same as a list of lists of symbols!)
• Do (but don't turn in) some of exercises 18.2.1, 18.2.2, 18.2.3, 18.2.4, 18.2.5, and 18.2.6.
  (Note: The printed book and the on-line book disagree on the problem numbers; the on-line book calls these 18.1.1, 18.1.2, etc.)
• Do exercise 18.2.15. (We did exercise 18.2.12 in class.)
• Do exercises 19.1.5 and 19.1.6.
• Develop a cooperating pair of functions named count-calls and reset. Each function takes no arguments (which means you need to be in Advanced Student mode to write them). reset returns nothing at all, while count-calls returns how many times it has been called since the last time reset was called. (Such a pair of functions might be used, for example, in a hit counter for a Web page.)
  Hint: Use a global variable, which both functions can modify, to keep track of the count.
• Develop a cooperating pair of functions named init and next. init takes in a list, and returns nothing. next takes in nothing, and returns the "next" element of the list that was given to init. For example,

  (init (list 'a 'b 'c)))
  (next)
  'a
  (next)
  'b
  (next)
  'c

  What do you think next should do if it is called a fourth time?

  Extra credit: Develop a single function named make-iterator which takes in a list and returns a function (like next, above) which steps through that list. This approach is more flexible, in that it allows you to have several different lists going at once, stepping through each one independently. For example,

  (define next-name (make-iterator (list 'joe 'mary)))
  (define next-class (make-iterator (list 'cs160 'math140 'eng107)))
  (next-name)
  'joe
  (next-class)
  'cs160
  (next-class)
  'math140
  (next-name)
  'mary
  (next-class
  'eng107

  Hint: You'll need at least one local variable, probably two, and perhaps a locally-defined function as well. It took me 7-10 lines of code, depending on what language features I used and whether I did error-checking.