EBoard 31: Data abstraction, revisited

Warning! You are being recorded (and transcribed).

Approximate overview

• Administrative stuff [10 min]
• Conceptual changes [10 min]
• A note from the SoLA [5 min]
• Questions [5 min]
• Lab [45 min]
• Turn in lab [5 min]

Administrative stuff

• Happy Monday!
• Apologies for any bad jokes today.

Token opportunities

Academic/Scholarly

• Tuesday, 2024-04-16, noon, some PDR. CS Table (topic TBD).
• Tuesday, 2024-04-16, 7pm, Science 3819. Mentor Session.
• Wednesday, 2024-04-17, 4:15–5:30pm, Burling 1st. Book Talk by Sharon Quinsaat.
• Wednesday, 2024-04-17, 5:00–6:00pm, HSSC A1231 (Kernel). GrinTECH Project Expo. What does TECH stand for?
• Thursday, 2024-04-18, 11am, JRC 101. Ruha Benjamin on “Viral Justice: How We Grow the World We Want”
• Thursday, 2024-04-18, 4pm, JRC 2nd Floor Lobby. CS Poster Session, Part 2.
• Thursday, 2024-04-18, 4:15–6:00pm, JRC 101. McKibben Lecture: Athenian Heroes: Re-reading the West Pediment of the Parthenon.
• Thursday, 2024-04-18, 7pm, Science 3819 Mentor Session.

Cultural

• Tuesday, 2024-04-16, 7:00–9:00pm, JRC 101. The Man Without a World.
• Friday, 2024-04-19, 4:00–5:00pm, HSSC N1170. Middle of Everywhere.
• Saturday, 2024-04-20, 2:00–5:00pm, Quad Dining Room. Japanese Spring Festival.

Peer

• Saturday, 2024-04-20, Noon–3:00pm, Pioneer Park. Baseball vs. Beloit.
• Saturday, 2024-04-20, 1:00–4:00pm, Park Street to the Bear. Carnivale. (Vegetarian festival, I believe.) But why does it take three hours to go one block?
• Saturday, 2024-04-20, 2:30–5:00pm, Pioneer Park. Baseball vs. Beloit, revisited.
• Saturday, 2024-04-20, 7:00–9:00pm, Herrick. Michael Londra and the Grinnell Symphony Orchestra.
• Sunday, 2024-04-21, 10:00am–1:00pm, Tennis Courts. Men’s Tennis vs. Coe.
• Sunday, 2024-04-21, noon–3:00pm, Pioneer Park. Baseball vs. Beloit, revisited. The Sequel!
• Sunday, 2024-04-21, 2:00–4:00pm, Sebring Lewis Hall. Grinnell Singers with a King Singer (Simon Carrington).

Wellness

• Monday, 2024-04-15, 4:00–5:00pm, HSSC Atrium. Therapy Dogs.
• Tuesday, 2024-04-16, noon-1pm, BRAC P103. HIIT and Strength Fitness Class.
• Tuesday, 2024-04-16, 12:15–12:50, Bucksbaum 131. Yoga in the Museum.
• Tuesday, 2024-04-16, 4pm, BRAC P103 (Multipurpose Dance Studio): Yoga.

Misc

• Tuesday, 2024-04-16, 4:00–5:30pm, HSSC N1112. Printmaking Workshop with Digital Studies. “Drinks and supplies included.”
• Saturday, 2024-04-20, 10:00am–1:00pm, Track and Field Complex. Dick Young Classic.
• Saturday, 2024-04-20, 8:00am–5:00pm, JRC 209. Mental Health First Aid Training. Let me know how many tokens you consider appropriate for a full-day event.
• Saturday, 2024-04-20, 11:00am–6:00pm, Mac Field. DAG Field Day. Why is DAG all caps?

Other good things (no tokens)

• Wednesday, 2024-04-17, 3:00–5:00pm, Softball Complex. Softball vs. Knox.
• Saturday, 2024-04-20, 1:00–3:00pm, . Softball vs. Ripon.
• Saturday, 2024-04-20, 3:00–5:00pm, . Softball vs. Ripon, revisited.

NO! You do not get tokens for Wonderland Harris.

Upcoming work

• Tuesday, 2024-04-16, 11:00pm, Reading on higher-order recursive design
  • Submit reading on Gradescope
• Wednesday, 2024-04-17, 8:30am, Lab writeup
  • Submit todays’s lab on Gradescope
  • Preferred: Finish it during class today.
• Wednesday, 2024-04-17, 11:00pm, MP7
  • Submit MP7 on Gradescope
  • Autograder should be ready tonight.
• Friday, 2024-04-19, 8:00am, Quizzes
  • Data abstraction (new).
  • Diagramming structures.
  • Tracing.
• Friday, 2024-04-19, 11:00pm, Post-reflection on MP7
  • Submit MP7 post-reflection on Gradescope
• Friday, 2024-04-19, 11:00pm, Pre-reflection for MP8
  • Submit MP8 pre-reflection on Gradescope
• Sunday, 2024-04-21, 11:00pm, Redo for MP6
  • Submit MP6 redo on Gradescope

Conceptual changes (making the implicit explicit)

Did you notice that we’ve encountered some significant conceptual changes in the way we use Scheme?

• Topical: We’re thinking more about structures.
• Abstraction: We’re also trying to abstract away from the representation. (Procedures also provide abstraction from the underlying implementation.)
  • You don’t have to worry about how map works; you can just use it.
  • Note: Soon, you’ll learn to write map.

We’ve moved from a world in which (fun args) always gives the same result to one in which (fun args) can give different results.

(define x 5) (sqr 5) .... (sqr 5)

Now (define vec (vector 'a 'b 'c)) (vector-ref vec 0) ... (vec-ref vec 0)

The second time through, we may not get 'a. “It depends on what we did in between.”

Programming is now “stateful”. It complicates analysis. It complexifies sequencing. (Order now matters significantly more than it did before.)

We therefore have to learn about ways to sequence operations other than just “inside out”.

What we know (or may know).

When you define a procedure, you can put more than one expression in the body.

(define proc
  (lambda (...)
    (step-one!)
    (step-two!)))

It will then evaluate them in turn, returning the value of the last one.

When you use cond, you can put more than one expression after the guard.

(cond
  [(guard)
   (step-one)
   (step-two)
   (step-three)]
  ...)

If the guard holds, it will then evaluate them in turn, returning the value of the last one.

When you use when, you can put more than one expression after the guard.

We now have multiple ways of sequencing operations:

• Inside-out for most expressions.
• Sequencing “this then this then this” in the bodies of cond, and procedures and let and when.
• Left-to-right for or and and (and maybe others)
• composition

Since we may now be calling procedures to change state (rather than compute a value). These procedures often return nothing. E.g., vector-set! (it changes state - the vale in the vector) but returns nothing.

OUR SUBSTITUTIVE MODEL HAS NOW BROKEN!

Reviewing randomness

What’s wrong with play-seven-eleven?

(define play-seven-eleven
  (lambda ()
    (cond
      [(= 7 (pair-a-dice))
       1]
      [(= 11 (pair-a-dice))
       1]
      [else
       0])))

Because we call pair-a-dice twice, we have slightly different odds. This is “roll the dice, compare to seven, roll again, compare to eleven”. (Take statistics to learn why the odds are lower.)

We can fix it with a let binding.

(define play-seven-eleven
  (lambda ()
    (let ([paradise (pair-a-dice)])
      (cond
        [(= 7 paradise)
         1]
        [(= 11 paradise)
         1]
        [else
         0]))))

Questions

Administrative

Are we permitted to use a page of notes on quizzes?

Of course.

Will we get SoLA 3 back soon?

Yes. Probably tonight.

MP7

Is MP7 fun and awesome?

Of course. Sam loves us.

Misc

Lab!

What should I know about sorting names?

The rules are at https://www.webpages.uidaho.edu/cte492/Modules/M7/12_Rules_of_Filing.pdf

Titles are the hard part, and may need a lot of effort.

“Father Jane” -> “Father Jane”

“Father Jane Smith” -> “Smith Jane Father” (or “Smith, Jane Father”)

“Mr. Sam” -> “Sam Mr”

“Mr. Sam Rebelsky” -> “Rebelsky Sam Mr” (or “Rebelsky, Sam Mr”)

Do I really have to get rid of spaces and apostrophes and such?

It would be nice, but it’s not strictly necessary.

Should I treat “Brother” like “Sister”? Should I treat “Mother” like “Father”?

I’m not sure. The guidelines are a bit abstract, aren’t they? But yes, I’d count them as the same. (They are, arguably, “Religous Titles”)

Should I treat “Deacon Smith” as “Deacon Smith” or “Smith, Deacon”?

It depends on whether “Deacon” is a first name or a title. I think.

Is it okay if the sort names aren’t perfect?

Yes.