EBoard 03 (Section 1): Mental Models

Reminders to Self

• Warning This class is being recorded.
• Post link to Otter.ai.

Getting started

• Same seat as last class.
• On Friday, we’ll return to our “normal” algorithm.

Approximate overview

• Administrative stuff [15 min]
• Second lab from last class (submit as “Lab Writeup from Class 2” on Gradescope) [n minutes]
• New lab, on paper (hand in on Friday). [(- 60 n) minutes]
• Debrief [5 minutes]

Administrivia

Introductory notes

• Our class site is still under development. Let me know if you find things missing, including images.
  • Those slash things on the syllabus usually indicate something that I plan to post. If they show up for a reading, let me know.
• Normal office hours are in-person (unless you’d prefer to do them remotely).
• Apologies: I have some significant personal issues that may make me less available in person in the coming weeks. I will do my best to be available via email and Teams chat.
  • These issues have also put me behind. Apologies for that, too.
• I have made two updates to the schedule:
  • We’re not doing a quiz this Friday; I don’t think we’ve covered enough.
  • I’ve moved the homework pre-assessment to Sunday night.
• I’m told that all the accounts are now set up. Let me know if you have difficulty logging in.
• Let me know if you don’t seem to be on the class team (Microsoft Teams).
• Fill out the mentor session poll at https://rg.by/pairj

HW 1

• Warning: Most of this is based on material we will cover Friday and Monday.
• I thought you’d benefit from seeing it early so that you can start thinking about it.

Upcoming Token activities

Academic

• Convocation, Thursday, 11:00 a.m. President Harris.

Cultural

• Drag Bingo, Saturday

Peer

• (No more volleyball scrimmages; let’s limit ourselves to competitions.)
• Volleyball game on Friday at 5:00 against Bethany and Dominca.
• Football a week from Saturday, 1pm, against Rippon.

Wellness

Upcoming work

• Two readings for Friday; Complete the reading assignment on Gradescope by Thursday night.
• Lab writeup(s) due before class on Friday.
• Homework one released (probably not doable yet).
• Homework one pre-assessment due on Sunday night (these will usually be due on Friday nights; I like you to think about assignments early).

Questions on the readings

Does it matter if there are newlines or extra spaces in the middle of an expression?

Not really. But don’t put them in the middle of, say, a number.

For the reading check, what did you want for subexpressions?

We’ll stick with parenthesized things.

(above (rectangle 60 40 "solid" "red")
       (beside (rectangle 60 40 "solid" "blue")
               (rectangle 60 40 "solid" "black")))

I’d list (rectangle ... "red"), (rectangle ... "blue"), (rectangle ... "black"), and (beside ...).

Arguably, 60, 40, “solid”, and such are also subexpressions, but that’s a lot to list.

Lab continued from Monday

New lab

• Note: Our evaluation model is leftmost-innermost; you move through the arguments from left to right, doing each inner-to-outer (and also leftmost-innermost).

Debrief on lab from Monday: MathLAN

• The origin of the short and long versions. My colleagues who first taught the course wrote the long versions (or at least the original versions of the long versions). When I started teaching, I decided you might do better with short instructions. But it’s a nice example of different ways of thinking about writing algorithms/instructions.

Debrief on lab from Monday: Scheme

• I see that many of you have three screens (our main screen plus two
• It’s generally a bad idea to skip ahead in the lab. laptops). Please do your work on the MathLAN workstation and just use your laptop for bringing up the lab/reference materials.
  • If I see you running DrRacket on your laptop, I may attempt to defenestrate aforementioned laptop.

Debrief on new lab

Does the evaluation order really matter?

You need to evaluate the parameters before you apply the procedure. (“innermost”).

But it turns out that it (generally) doesn’t matter whether you evaluate them left-to-right, right-to-left, or some strange hybrid of the two.

For convenience, we’ll generally focus on left-to-right.

Brain teasers

What do you expect to get for (+ 4*4 4*4)?

What do you expect to get for (+ x -x)

Terminology

Yea, we need to work on it.