• New partners (for real today!)
• Chocolate!

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Questions and answers.
• Some notes on yesterday's lab.
• Some key ideas from the reading.
• Lab.

Preliminaries

Admin

• Office hours today and next week
  • Mostly Normal (Th 1:45-3:15; walking 1:15-1:45); No hours on Friday
  • Mornings I will be in various places. If you want to find me, email me.
• Review sessions tonight at 8pm, Thursday at 10 am, Thursday at 8pm.

Upcoming Work

• Writeup: Problem 3 (due Friday): http://bit.ly/151-2014F-w28
• Exam 2 due NOW!
  • Epilogue due tonight
• Reading for Friday:
  • Numeric Recursion
• Friday's quiz: Identify your classmates. (I provide first names and a set of pictures.) No notes permitted. Ten minutes.

Cool Events

• Concert tonight!

Extra Credit Opportunities

Academic

• CS Table, Friday: Hear about the Grace Hopper Celebration of Women in Computing.

Peer Support

• Football (Saturday at 1pm)
• Swimming October 18: Alumni Weekend
• Karan's radio show 11pm Thursday nights on KDIC
• Evan's radio show 5pm Friday nights on KDIC
• Donna's radio show Sunday midnight on KDIC
• Men's Tennis (???)
• Women's Tennis (???)

A Quick Note/Demo on Indentation

• For the students who bring me code for exam questions, one of the first things I do is reindent the code. Why? Because indentation often tells you when you have mismatched parentheses.
• Let's look at an example.

Comments on Academic Honesty

• Small things can still be academically dishonest
• For fairness: Individual faculty should not make the decision
• And it's almost break, so think good thoughts!

Questions (Administrative)

Questions and answers

Lab

What's the base case for largest?

It's easy to find the largest value in a single-element list. It's hard to find the largest value in a zero-element list.

I heard the mentors say "Oh, that's a different largest than I expected". What are the different ways that people write largest?

    (define largest-a
      (lambda (lst)
        (if (null? (cdr lst))
            (car lst)
            (max (car lst) (largest (cdr lst))))))

    (define largest-b
      (lambda (lst)
        (largest-b-helper (car lst) (cdr lst))))

    (define largest-b-helper
      (lambda (largest-so-far remaining)
        (if (null? remaining)
            largest-so-far
            (largest-b-helper (max largest-so-far (car remaining))
                              (cdr remaining)))))

I want to locally bind a non-recursive procedure called irgb-darker so that I can apply the pattern from problem 3.

Certainly

    (define irgb-darkest
      (let ([irgb-darker (lambda (color1 color2)
                           (if (> (irgb-brightness color1)
                                  (irgb-brightness color2))
                               color1
                               color2))])
        (lambda (colors)
          ...)))