CSC 151 2019S, Class 13: Local bindings

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Friday PSA
  • Questions
• Quiz
• Lab
• Debrief (maybe)

Preliminaries

News / Etc.

• Mentor sessions Wednesday 8-9 p.m., Thursday 8-9 p.m., Sunday 5-6 p.m.
• Warning! It’s Friday the 13th (class). Bad luck is possible.
• Note: It is a useful habit to reflect back after each exercise and ask yourself “What did the exercise designer want me to take from this exercise?”
• Since it seemed unclear to some of you: Your are not finished when you do the lab writeup. You should look at (and, if possible, do) all of the exercises in each lab.
• With four students gone, we may need to reshuffle a bit after the quiz.
• I think I’ve now set things up so that the formatted eboard auto-updates every five minutes during class.

Upcoming work

• There is no reading for Monday!
• Assignment 5 due next Tuesday.
  • Your homework partner is your partner from Wednesday’s class
• Flash cards due Wednesday at 8:00 p.m.
  • Covers Wednesday/Friday/Monday classes
• Quiz next Friday: Randomness and Local Bindings

Extra Credit

Extra credit (Academic/Artistic)

• Iowa Flautists in Concert. Saturday, 23 February 2019. 3:45 p.m. Sebring-Lewis Hall.

Extra credit (Peer)

• Last Chance Swim and Dive, Saturday at about 10:30 ec.
• Men’s BBall, Friday, 3:00 p.m. vs. LFC at St. Norbert. (Hopefuly a Saturday game, too.)
• Indoor Track and Field, Friday and Saturday, at Monmouth.

Extra credit (Wellness, Regular)

• 30 Minutes of Mindfulness at SHACS every Monday 4:15-4:45
• Any organized exercise. (See previous eboards for a list.)
• 60 minutes of some solitary self-care activities that are unrelated to academics or work. Your email reflection must explain how the activity contributed to your wellness.
• 60 minutes of some shared self-care activity with friends. Your email reflection must explain how the activity contributed to your wellness.

Extra credit (Misc)

Other good things

Friday PSA

Be happy. Be good. Be well. Be true to yourself.

Consent is essential.

Questions

Quiz

If you find that you finish early, take some time to meditate quietly. Alternately, you may go get a drink of water or use the rest room.

Lab

Remember to review the self-checks! (More generally, remember to do the self-checks!)

Debrief

I can fantasize that we’ll have time to debrief, can’t I?

What is the “moral” of the define-vs-let exercise?

Using define within another definition does not always behave as we expect.

More broadly, the semantics of define are a bit more complex than the semantics of let.

Therefore, we recommend that you do not use define within another define. (Use let or let* instead.)

However, we must admit that the designers of Racket prefer nested define expressions to let.

What were the “morals” of exercise 5?

If you are defining values that are independent of the parameters to a procedure, the (let ... (lambda ...)) form is more efficient.

Sam lied! Although Sam claimed that the definitions disappear when the let finishes, in point of fact, they remain available in the body of procedure, just nowhere else!

How can we simulate that stupid nested let with a map?

How Sam and others might do 2b

    (map (o (section * 7 <>) (section expt 2 <>)) 
            (range 5))
    (map (lambda (x) (* 7 (expt 2 x))) 
         (range 5))

Can we explore the define thing a bit more?

    ; This doesn't work
    (define sample-w/define
      (lambda (x)
        (define x (+ x 1))
        (list x x x)))

    ; What do you expect for this?
    (define sample-w/define
      (lambda (x)
        (define y (+ x 1))
        (list y y y)))