• New partners!

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• What's going on with irgb-brightest?
• Lab.

Preliminaries

Admin

• Friday the 13th falls on Friday this week. Be careful!
• Review sessions 9am, 1:15pm, and 8:00pm Thursday.
  • I can answer general exam questions in the daytime sessions.
• Office hours again mostly normal (MTWF 10:00 plus afternoons).
  • http://rebelsky.youcanbook.me

Upcoming Work

• Exam 2.
  • Electronic version due 10:30 p.m. Thursday the 12th.
  • Epilogue due 11:00 p.m. on Thursday the 12th.
  • Printed version due start of class on Friday the 13th.
  • But I will make accommodations if you are over your head with work or life.
• Reading for Friday:
  • Numeric Recursion
• Quiz Friday!

Extra Credit Opportunities

Academic

• CANCELLED: Town Hall on Town Halls, noon or 7:30 p.m. today
• Amy Johnson '85 concert tonight at 7:30 p.m. in Herrick.
• CS Table Friday - Debrief from Tapia Celebration of Diversity in Computing
• Post-break: April 1 Scholars Convocation on Implicit Bias.

Peer Support (Morning Section)

• Julia's radio show, "The Hot Box". Wednesday night/Thursday morning 1:00-2:00 a.m. THAT'S TONIGHT. Happy songs, because you need them.

Questions

Can you help me think about the tests in problem 6?

You will need to write tests that use particular colors, colors which you will normally create with irgb.

Your main check is "Did irgb-classify classify it correctly?"

For example

    (check-equal? (irgb-classify (irgb 200 201 200))
                  'greenish
                  "large, close, values; red=blue; green dominates")

I'm getting a weird "quark" error in problem 8. Can you tell me why

You are probably generating a y value outside of the valid range. Try generating the list of y values and scanning it for negative numbers or values greater than height-1.

Computers are sentient and malicious.

How long is "long" for lists when we are checking rdc and rac?

10,000 or so would be good to test.

What's going on with irgb-brightest?

(define irgb-brightest
  (lambda (colors)
    (cond
      [(null? (cdr colors))
       (car colors)]
      [(>= (irgb-brightness (car colors)) 
           (irgb-brightness (irgb-brightest (cdr colors))))
       (car colors)]
      [else
       (irgb-brightest (cdr colors))])))

Lab

The pattern you choose is important!

Please do NOT use the following form

    (define largest
      (lambda (lst)
        (cond
          [(null? (cdr lst))
           (car lst)]
          [(max (car lst) (largest (cdr lst)))])))

• Why not?
  • Only two choices: Use an if expression
  • Always put else before your default

• So write

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

Pun of the day

• Instead of irgb-all-bright? you can write irgb-madeleine?