EBoard 05: Mental models
Warning! You are being recorded (and transcribed) (provided the technology
is working correctly).
Approximate overview
- Administrative stuff, including attendance [25 min]
- Reading overview [10 min]
- Lab [40 min]
- Turn in lab [5 min]
Administrative stuff
- My goal is always to do these in fifteen minutes or less. I rarely succeed.
- I am usually spending the time right before class making sure that
everything is ready. Don’t expect to be able to ask me questions.
- Welcome to our newest class member!
Attendance
Yes, we’ll do that once in a while.
Upcoming activities
Scholarly
- Thursday, 2024-02-01, 11am, HSSC 2231 (Auditorium),
Scholars’ Convocation, Being a Pandemic Citizen.
- Thursday, 2024-02-01, 4:00pm, Science 3821:
CS Extras: Summer research.
Cultural
Peer
- Friday, 2024-02-02, 8pm, Harris Concert Hall:
Weekend Murder Mystery. There’s food. You get to solve puzzles.
The winner(s) will get prizes.
- Saturday, 2024-02-03, Natatorium:
Swim meet.
Wellness
Misc
Other good things
Upcoming work
- Wednesday, 2024-01-31, 11:00pm: Mini-Project 1 due.
- Thursday, 2024-02-01, 11pm: Read things in preparation for the sixth day of
class and report on those things
- Friday, 2024-02-02, Class time: Quiz
- New quiz: Tracing
- Quiz redo: Decomposition
- You can arrive as early as 7:45 a.m. if you’d like to take both quizzes.
- Quizzes must be done by 8:45 a.m.
- Friday, 2024-02-02, 8:30am: Submit today’s lab writeup.
- Preferred: Submit before the end of class today.
- It’s paper. You must hand it to me.
- Friday, 2024-02-02, 11pm: Mini-project 1 post-refelection due.
- Friday, 2024-02-02, 11:00pm: [Mini-project 2 pre-reflection(https://www.gradescope.com/courses/690100/assignments/4030975) due.
- Wednesday, 2024-02-07, 11:00pm: Mini-Project 2 due.
Notes on Monday’s lab
Stopping with five minutes to go.
In general, I’ll tell you to stop when there are five minutes left.
- Different people will have accomplished different amounts.
- I strongly encourage you to try to finish the lab on your own. At
least one student from last semester said I should force you to
finish the lab on your own. (We’ll revisit why I don’t.)
- It’s okay if you don’t pass all the tests. However, it’s nice to
have an idea why you haven’t passed the test.
- You will generally get an “S” (1.0 or .9999) if you submit something.
The joy of ctrl-up-arrow (or Esc-P)
- There is a command history.
- You can get to prior commands Ctrl-UpArrow
- That doesn’t work on the Mac, because Ctrl-UpArrow already has
a meaning.
- You can also get prior commands with Esc-P.
- Use Ctrl-I to reindent.
Ways to define snowperson and snowperson-revisited
(define snowperson
(lambda (size)
(above (outlined-circle (* 2/5 size) "black" 1)
(outlined-circle (* 3/5 size) "black" 1)
(outlined-circle (* 5/5 size) "black" 1))))
(define snowperson-revisited
(lambda (height)
(above (outlined-circle (* 2/5 1/2 height) "black" 1)
(outlined-circle (* 3/5 1/2 height) "black" 1)
(outlined-circle (* 5/5 1/2 height) "black" 1))))
vs.
(define snowperson-revisited
(lambda (height)
(snowperson (* 1/2 height))))
TPS: Is this better than the old snowperson? Worse? The same?
- This is more concise, which is nice. It’s also easier to write.
If we realize that the circle ratio in
snowperson is wrong,
there’s only one set of code to fix.
- This could be confusing to the reader.
- Documentation would help.
- There’s no guarantee that
(snowperson size) always creates a
snowperson whose height is (* 2 size).
- The documentation adds that guarantee, too.
- Please don’t swear in my class.
;;; (snowperson size) -> image?
;;; size : positive-real?
;;; Creates a snowperson whose bottom snowball is `size`
;;; and whose overall height is `(* 2 size)`.
;;; (snowperson-revisted height) -> image?
;;; height : positive-real?
;;; Create a snowperson of the specified height
(define snowperson-revisited
(lambda (height)
(snowperson (* 1/2 height))))
vs.
(define snowball
(lambda (diameter)
(outlined-circle diameter "black" 1)))
(define snowperson
(lambda (size)
(above (snowball (* 2/5 size))
(snowball (* 3/5 size))
(snowball (* 5/5 size)))))
vs.
Questions
Administrative
Do you mind if we point out the plethora of mistakes on your Web pages?
I’ve found typos, broken links, bad HTML and more.
Let me know. I would prefer to correct them. Perhaps you’ll even
earn a token.
I also appreciate you using the word “plethora”.
Can we use Scamper instead?
No.
Can we use our own computers?
Yes. You can download DrRacket onto your laptop/desktop and do your
work there.
You can also remote login to MathLAN. Talk to me if you want to do so.
Are there limits to how many tokens we can earn in a particular category?
No.
Does it matter what category a token activity is in?
No.
Reading
Reading overview
TPS: What are the key points of the readings?
- UM: Understand Mechanisms
- Understand how Racket interprets expressions and procedures
- We trace to follow that understanding.
- Also clarifications of terms like “procedure” and “identifier”
- We rely on parentheses to group things. Validate that they match
correctly.
- We generally use the innermost parenthesized expression first and
then move outward. We also move left to right.
(+ (* 3 4) (sqr (+ 1 2)))- We would normally evaluate the
(* 3 4) first.
We prioritize “left to right” over “innermost first”.
-
We use arrows to show our trace
(+ (* 3 4) (sqr (+ 1 2)))
--> (+ 12 (sqr (+ 1 2)))
--> (+ 12 (sqr 3))
--> (+ 12 9)
--> 21
-
When tracing user-defined functions (with a lambda), plug the arguments
into the body of the procedure, and then put the new thing into the
trace.
(define square
(lambda (x)
(* x x)))
(+ (square 5) (square 7))
--> (+ (* 5 5) (square 7))
--> (+ 25 (square 7))
--> (+ 25 (* 7 7))
--> (+ 25 49)
--> 74
- Make sure you evaluate all of the parameters to a procedure before
doing that substitution.
Lab
I’m not sure why trace isn’t working for some of you. I hate computers.