• New partners!
• More food-like substances.

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• A bit more about visual (and actual) representations of pairs and lists
• Lab.

Preliminaries

Admin

• Exercise 1 on today's lab is intended to get you thinking carefully about what it means to change values in Scheme.
• Review sessions this week:
  • Monday, 8pm (Zachary)
  • Wednesday, 8pm (Caleb)
  • Thursday, 10am (SamR)
  • Thursday, 8pm (Erin)
• Office hours this week and next: MWF 8:30-9:00, 11:00-11:45, 1:00-2:00; Tu 1:00-2:00; http://rebelsky.youcanbook.me
• Tuesday's reading is not yet ready. Expect it this afternoon.

Upcoming Work

• Reading for Tuesday: Binary Trees
• Exam 3 due tomorrow at 10:30 p.m.
• Exam 3 epilogue due Wednesday at 10:30 p.m.
• Today's Lab writeup (due before class Wednesday)
  • Email to grader-151-01@cs.grinnell.edu
  • Subject: CSC 151 Lab Writeup Class 38 (Your Names)
  • Exercises:

Extra Credit Opportunities

• If possible, send me these in advance.

Academic

• Any visit to the current show in the Faulconer gallery.
• Learning Deconstructed Workshop Series, Tuesdays at 11 in JRC 209.
• CS Table Tuesday: Cryptographic Back Doors.
• Wilson talk Wednesday: Startup (in)Sanity. 7:30 p.m., ARH 102.
• CS Extras Thursday: Developing and Deploying Mobile Sensing Applications.

Miscellaneous

• Any of the Queer Culture Week events (including pub quiz).

Peer Support

• Friday, 8pm, Comedy Show in Bob's.
• Orchestra Concert, November 14, Sebring Lewis, 7:30 p.m.
• Women's Basketball Opening Game, 1 pm, Nov. 15, vs. Silver Lake.
• ISO Food Bazaar. Nov. 15, 5-7 pm, Harris Gym/Concert Hall.

Regular Peer Support

• Pals of PALS, pals@grinnell.edu, normally Saturday at 7:45 am (breakfast included; felines only), and Mondays at 4:45. Requires sign up in advance. MORE HELP NEEDED!
• Socrates Cafe', Saturdays, Younker, 2pm.
• Pun Club, Saturdays, 4pm, Way over Younker.

Upcoming Peer Support

• Translations (a play). Nov 19-23 or so.
• One-act Festival Dec. 5 & 6.

Questions

On problem 5, is it okay if the brush is thicker than the one in the exam?

Yes.

Why is it thicker?

At some point, GIMP changed the default brush.

Pairs, Etc.

Why are we doing pairs? A few reasons.

• Get a "behind the scenes" understanding of lists. Scheme really does build these structures with two boxes, each of which references something else.
• Translating code to pictures and back again.
  • Any cons is one pair.
  • Almost every null is a slash within a pair.
  • Anything else, we draw an arrow to.
• How do we decide if something is a list?
  • Base case: null
  • Recursive case: x is a list if the cdr of x is a list. (Because you make a list by consing something on to the front of a list.)

Lab