CSC 151.03, Class 20: Other forms of list recursion

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Questions
• Problem 6 from Friday’s lab
• DrRacket tips and tricks
• Reading summary
• Lab
• Debrief (?)

News / Etc.

• I have not received all grades from the graders. I have not finished my own grading for CSC 151. I brought food instead. I should have some grades on Wednesday.
• “Is it normal to need to ask questions on the exam?” Yes.
• “I feel like I’m asking a lot.” Some folks ask a lot. Others don’t. Don’t stress.
• “Can you talk about cool DrRacket tricks?” I’m not sure that any of them are cool, but I’ll go over the ones that come to mind.

Upcoming Work

• Writeup for class 19 due TODAY at 10:30 p.m.
  • Exercise 4
  • To: csc151-03-grader@grinnell.edu
  • Subject: CSC 151.03 Writeup 19 (YOUR NAMES)
• Writeup for class 20 due Wenesday at 10:30 p.m.
  • Exercise 4 (no documentation necessary)
  • To: csc151-03-grader@grinnell.edu
  • Subject: CSC 151.03 Writeup 20 (YOUR NAMES)
• Exam 2 due Tuesday at 10:30 p.m..
• Exam 2 cover sheets due Wednesday at the start of class
• Exam 2 epilogue due Wednesday at 10:30 p.m.

Extra credit (Academic/Artistic)

• Aspen Trio on Wednesday at 7:30 p.m.

Extra credit (Peer)

Extra credit (Misc)

Other good things

• Volleyball vs. U. Dubuque Tuesday at 7:00 p.m.

Questions

What’s the time limit on extra credit?

A few days.

But I have been known to take them a month late.

I wouldn’t recommend pushing your luck. Strive for soon.

Problem 6 from Friday’s lab

(define furthest-from-zero-alt
  (lambda (numbers)
    (display (list 'furthest-from-zero-alt numbers)) (newline)
    (if (null? (cdr numbers))
        (car numbers)
        (if (>= (abs (car numbers)) 
                (abs (furthest-from-zero-alt (cdr numbers))))
            (car numbers)
            (furthest-from-zero-alt (cdr numbers))))))

Solution?

(define furthest-from-zero-alt
  (lambda (numbers)
    (display (list 'furthest-from-zero-alt numbers)) (newline)
    (if (null? (cdr numbers))
        (car numbers)
        (let ([result-from-magic-recursion-fairy
               (furthest-from-zero-alt (cdr numbers))])
          (if (>= (abs (car numbers))
                  (abs result-from-magic-recursion-fairy))
              (car numbers)
              result-from-magic-recursion-fairy)))))

DrRacket tips and tricks

See the handout.

Reading summary

Skipped.

Lab

Writeup: Exercise 4, no documentation.

Debrief

Skipped.