Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Questions.
• Lab.

Preliminaries

Admin

• Continue partners!
• Quiz 5 returned.
• Upcoming review sessions
  • Wednesday at 8pm
  • Thursday at 10am
  • Thursday at 8pm

Upcoming Work

• Reading for Wednesday: Recursion Basics
  • Warning! For some, this will be even more confusing than section. For others, it will be intuitive. We will spend a few weeks trying to make it intuitive for everyone.
• HW 5 due Wednesday.
• No Lab Writeup Today.
• Exam 2 distributed.
  • We'll go through it quickly.
  • I'm not sure when CC is posting his version, but our problems should be the same even if our policies aren't necessarily.
  • Probably lots of opportunities for corrections :-)

Extra Credit Opportunities

• If possible, send me these in advance.

Academic

• CS Extras Thursday: Blake Creasey on Watson

Other Good Things

• Poet 8pm Thursday somewhere on campus. Probably at Bucksbaum. Look for the huge crowds that poets normally draw at Grinnell.
• Friends of Drake Library book sale this weekend. Community room. Friday 5-8 pm. Saturday 8am-2pm. Admission $3 on Friday and $0 on Saturday. HC $1, PB $0.50. Books usually $1/box after some time on Saturday (noon?).
• Social event known as 10-10. Please behave responsibly; do not over-consume know your limits, CONSENT IS NECESSARY (and difficult if impaired)
• Spanish speaker (in Spanish) 4pm in ARH 102 on Dueling as a writing process (or vice versa)

Questions

When I'm picking the random column and row, what range should I choose from?

For the column, it should be a number between left and left+width-1.

But random only gives me a value between 0 and n-1.

Think about how to transform one range to another. (Hint: Addition.)

Do I need to document the procedures in part 3?

Yes. But you can use just 4P's.

Lab

No Lab Writeup Today!

Lesson 1: You can only take the car of non-empty lists and things created with cons.

Lesson 2: You can only use up to four middle letters in the silly cddddr procedures.

Lesson 3: Computer scientists often start numbering at 0, rather than 1. That's somewhat nice for how we write procedurees, since to get element 5 of a list, we have to call cdr 5 times.

Lesson 4: Scheme lets you create things that aren't lists. These things show up with a dot in the middle. Be careful when you have such things; they will sometimes, but not always, lead to errors when you use them like lists.

    > (cons 1 (cons 2 3))
    > (append (iota 50) 1)

Lesson 5: car and cdr work with the "not quite list" things. They are officially defined with the rules

    (car (cons a b)) = a
    (cdr (cons a b)) = b

Note 6: For problem 5, consider

    (cons 'drawing (cons 'rectangle (cddr drawing)))