EBoard 23: Recursion (Section 3)

Please follow the standard start-of-class routine.

Warning! You are being recorded (and transcribed) (provided the technology is working correctly).

Approximate overview

• Administrivia
• Pop quiz
• Lab

Administrative stuff

Introductory Notes

• If you haven’t done so already, feel free to grab a duck from the back of the room.
• We’re returning to the “Sam talks less” experiment.
• I’m also continuing the “pop quiz” experiment.
• Today’s lab is likely too long, even with “Sam talks less”.
• The second redo of MP1 is now due a week from tomorrow. The first redo should be returned by Sunday.
• MP4 will be ready tonight. It involves writing lots and lots of recursive functions that process lists of colors. (Getting all the details right is taking a bit more time than I’d been able to allocate.)

Upcoming work

• Due Thursday, 2026-10-27
  • Read Tail recursion
    • Submit reading response on Gradescope
  • Submit lab writeup on Gradescope
• On Friday, 2026-10-30
  • NEW Quiz/LA on list recursion (today and Friday)
  • Makeup Quiz/LA on testing
  • Makeup Quiz/LA on local bindings
  • Makeup Quiz/LA on collaboration
  • Makeup Quiz/LA on lists and list operations
  • Makeup Quiz/LA on conditionals
  • Makeup Quiz/LA on compose, cut, and section
  • Makeup Quiz/LA on tracing
  • Makeup Quiz/LA on decomposition
  • Makeup Quiz/LA on procedures
• Due Tuesday, 2026-11-03
  • Mini-project 4
    • Submit MP4 on Gradescope
• Due Thursday, 2026-11-05
  • Mini-project 1 second redo
    • Submit redo on Gradescope
    • When submitting a mini-project redo, please include a file called CHANGES.txt that describes what you’ve changed.

Upcoming activities

Scholarly

• Thursday, 29 October 2026, 11:00 a.m.–Noon, JRC 101. Scholars’ Convocation: Dan Reynolds on Are We There Yet? The Humanities as a Journey
• Thursday, 29 October 2026, 4:15–5:15 p.m., Noyce 3821. CS Extras: Student presentations
• Tuesday, 3 October 2026, Noon–1:00 p.m., JRC 224C (I think). CS Table

Artistic/Cultural

• Any day. Visit the GCMOA for at least 30 minutes.
• Thursday, 29 October 2026, Noon–1:00 p.m. Bucksbaum 263 - Fitzgibbons Music Seminar. Total Immolation: Gamelan Towards the Collapse of the Sun.
• Thursday, 29 October 2026, 4:00–5:30 p.m., Wall Theatre. Acting Through Musical Song Workshop with Rachel Kelsey
• Saturday, 31 October 2026, 7:30–10:30 p.m., Harris Cinema. RHPS
• Saturday, 31 October 2026, 8:00–9:00 p.m., Gardner. James Ivy and Band
• Saturday, 31 October 2026, 8:00–9:30 p.m., Herrick. Halloween “Spooktacular” Organ Concert (I’m not sure which organs they are playing; perhaps hearts and lungs.)

Multicultural

• Friday, 30 October 2026, 4:10–5:00 p.m., HSSC N1170. Middle of Everywhere (Chinese Ghosts)

Peer

Musical, theatric, sporting, academic, and similar events involving this section’s students are welcome.

Wellness

• Monday, 2 November 2026, 8:00–9:00 p.m., Prayer Garage in the CRSSJ. Meditation Group
• Tuesday, 3 November 2026, 12:15–12:45 p.m., GCMoA. Yoga in the Museum
• Tuesday, 3 November 2026, 4:30–6:00 p.m., Bear P103. Wellness Yoga
• Tuesday, 10 November 2026, 5:00–8:00 p.m., HSSC North Auditorium. Therapy Dogs

Misc

• Fill out the College AI survey at https://bit.ly/ACM-AI-Survey. There’s no need to submit evidence; just a reflection.
  • Friday deadline.
• Wednesday, 28 October 2026, 4:30–6:30 p.m., Burling. Open Education Trick or Treat
• Wednesday, 28 October 2026, 4:30–6:30 p.m., Harris Concert Hall. Grinnell Gathers: Volunteer Fair
• Wednesday, 28 October 2026, 5:00–7:00 p.m., JRC 209. QuestBridge Slime Event
• Wednesday, 28 October 2026, 8:00–9:00 p.m., Science 3820. Mentor Session
• Thursday, 29 October 2026, 8:00–9:00 p.m., Science 3820. Mentor Session

Other good things

These do not earn tokens, but are worth your consideration.

• Friday, 30 October 2026, 7:00–9:00 p.m. Darby Gym. Volleyball vs. Beloit
• Saturday, 31 October 2026, 11:00 a.m.–1:00 p.m., Springer Field. Men’s Soccer vs. Cornell College (last home match of the season)
• Saturday, 31 October 2026, 1:00–3:00 p.m. Darby Gym. Volleyball vs. Lake Forest (senior day)
• Saturday, 31 October 2026, 1:30–3:30 p.m., Springer Field. Women’s Soccer vs. Cornell College (last home match of the season)

Pop quiz

• Testing: What are the parameters to test-case? (You need not get them in the correct order.)
• Anonymous functions: Rewrite (lambda (x) (- 2 x)) with l-s or r-s.
• Characters: What is (integer->char (+ 3 (char->integer #\a)))?
• Lists: What is (cdr (cons 1 (list 4 5 6)))?
• Lists: What should you get from (map + (list 1 2 3) (list 4 4 4))?

Lab

When it says “Document, write tests for, and implement”, we’d prefer that you do things in that order.

• Documenting helps you make sure you know what the procedure should do.
• Writing tests helps you think even more carefully about such issues.
• Evidence suggests we are more likely to write correct code if we’ve thought about what the procedure should do before we implement the procedure. (Overall, we’re more efficient.)

Thinking about alphabetically-first

• Example 1: (alphabetically-first (list "eh" "bee" "see"))
  • Recursive call will be (alphabetically-first (list "bee" "see"))
  • Recursive result will be “bee”. (Trust the MRF)
  • We return ??? because ….
• Example 2: (alphabetically-first (list "a" "c" "b"))
  • Recursive call will be (alphabetically-first (list "c" "b"))
  • Recursive result will be “b”. (Trust the MRF)
  • We return ??? because ….