• Continue partners!

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Lab.
• Reflection.

Preliminaries

Admin

I did not take time last week to condemn the postings on Yik Yak because I thought the president's statement sufficed. But it sounds like individual voices are necessary, too. And, as a technologist, I have particular responsibility to comment in this case. So I should have done so more promptly. I apologize for the delay, particularly because this issue is very important to me.

Let me make it absolutely clear. Use of any medium - social, physical, virtual - to denigrate other people for their characteristics is completely unacceptable. I have updated our course front door to clarify this perspective. (If you have comments on how to better phrase my policy, I would appreciate them.)

• No daytime review sessions on Thursday. Evening review session at 8:00.
• Office hours today at 3:15-4:30.
  • http://rebelsky.youcanbook.me

Upcoming Work

• Homework 6.
  • Optional! Replaces lowest homework grade.
  • Due tonight at 10:30 p.m.
  • If you don't do the homework, promise to get two hours of extra rest. (No message necessary.)
  • I will distribute an answer key to the homework by Sunday night.
• Exam 2 released at 5:00 p.m. today. Due 10:30 p.m. Thursday the 12th.
• Reading for Wednesday:
  • Verifying Preconditions
• Friday's quiz: Pictures!
  • No, you don't have to get everyone. About 85% correct will earn you full credit.
  • Doing better than me or the mentors will also earn you extra credit.

Extra Credit Opportunities

Academic

• Any of the disability activities this week.
• David Berliner lecture Thursday at 7:00 p.m. in Harris.
• CS Table Friday - XKCD
• Town Hall on Town Halls, noon or 7:30 p.m. on March 11.
• Post-break: April 1 Scholars Convocation on Implicit Bias.

Peer Support (Afternoon Section)

• Belly Dancing Club Wednesday, 7-8 p.m. in Bucksbaum Dance Studio.
• Panel at 4:15 for National Womens' Week on Women in the Global Economy
• Men's Tennis Saturday at 9:00 and 4:30 in the Bear Field House
• Tour Flanagan Theatre to see how it has been transformed for Nobody Gets Hurt.

Miscellaneous (Extra Credit)

• Fill out the American College Health Association's National College Health Assessment survey. (Yes, your response can be "I filled out the survey.")

Other Good Things (No Extra Credit)

• Orchestra Saturday at 2 p.m. in Sebring-Lewis: Musicals, Show Tunes, and Soloists.

Questions

How should we ask whether a list has one element?

(null? (cdr lst))

Do not use (= 1 (length lst))!

When will we get the quizzes back?

Wednesday, I hope. Otherwise Monday.

Lab

One of the mentors wants to see you write riffle, which is the last problem in the extras session.

I don't care what value you give for (product null), so choose whatever is most helpful for you.

There are at least six different correct answers I've seen for irgb-tally-darks.

Debrief

Two approaches to product

(define product
  (lambda (lst)
    (if (null? lst)
        1
        (* (car lst) (product (cdr lst))))))

(define product
  (lambda (lst)
    (if (null? (cdr lst))
        (car lst)
        (* (car lst) (product (cdr lst))))))

Two ways to code riffle

(define riffle
  (lambda (first second)
    (cond
      [(null? first) second]
      [(null? second) first]
      [else (cons (car first) 
                  (cons (car second) 
                        (riffle (cdr first) (cdr second))))])))

(define riffle
  (lambda (first second)
    (if (null? first)
        second
        (cons (car first) 
              (riffle second (cdr first))))))