EBoard 26 (Section 1): Structured Types

Approximate overview

• Administrative stuff [~5 min]
• Racket stuff [~5 min]
• Questions [~15 min]
• Lab [~55 min]

Administrivia

Introductory notes

• We may have admitted students today (and over the next few weeks).
  • It appears that someone/something wants to warn admitted students about Grinnell weather.
  • Nope, no visitors today.
• Note that we will not have a Wednesday mentor session since SoLA 3 will be live.
  • Sunday and Monday’s mentor sessions will be reviews for the SoLA.
• If you have not yet done so, please sign up for an individual site on https://sites.grinnell.edu.

Class mask policy

• We will continue to wear masks until at least the next course survey (that is, through Friday the 15th).

Reminders

• Please say your name when you ask or answer a question (even if I’ve just called you by name).
• Evening tutors are available 7–10 p.m. Sunday through Thursday as well as 3–5 p.m. on Sunday.
• Mentor sessions are Monday 8–9 p.m. Wednesday, 8–9 p.m., Sunday 4–5 p.m.

Upcoming work

• ASAP: Sign up for a site on https://sites.grinnelledu
• Sunday 4:00 p.m.: Quiz 9: Vectors (Distributed this a.m.)
• Sunday 10:00 p.m.: Readings for Monday
• Sunday 10:30 p.m.: Today’s lab
  • Likely “Sam says stop here”
• Thursday, April 14, 10:30 p.m.: SoLA 3
  • Don’t forget that there are sample questions on the LAs page.

Upcoming Token-Generating Activities

• Saturday 1pm, Softball vs. University of Wisconsin Stevens Point
• Saturday 3pm, Softball vs. University of Wisconsin Stevens Point
• Wednesday, April 13, all day: Scarlett and Give Back Day
  • Token for donating. (Equity: You can grab $5 from me to donate.)
    • Recommend: Food Pantry, Student Mental Health, Accessibility
  • Token for participating in an activity.
• Wednesday, April 13, 8pm, Writers@Grinnell: Jerald Walker, https://grinnellcollege.zoom.us/j/85126108306

Other Upcoming Activities

• Sunday 2pm, Grinnell Singers, Sebring Lewis

Racket/Lab Stuff

name->sortable

(define name->sortable
  (let ([space-before (lambda (str) (if str (string-append " " str) ""))]
        [space-after (lambda (str) (if str (string-append str " ") ""))])
    (lambda (name)
      (let ([prefix (name-prefix name)]
            [given (name-given name)]
            [middle (name-middle name)]
            [family (name-family name)]
            [suffix (name-suffix name)])
        (cond 
          ; Normal case: They have a family name.  It comes first.
          [family
           (string-append family
                          ", "
                          given
                          (space-before middle)
                          (space-before suffix)
                          (space-before prefix))]
          ; Special case: Royalty and Religious, generalized
          [(not middle)
           (string-append (space-after prefix)
                          given
                          (space-before suffix))]
          ; Special case: No family but middle
          [else
           (string-append given
                          (space-before middle)
                          (space-before suffix)
                          (space-before prefix))])))))

Acknowledgements

;; Acknowledgements:
;;   List of space related words that helped me create my syllex
;;      https://relatedwords.io/space
;;
;;   Racket documentation for `member,` which was really useful for the maddish libs
;;      https://docs.racket-lang.org/reference/pairs.html
;;   Project Gutenburg record of Alice's Adventures in Wonderland by Lewis Caroll
;;      https://www.gutenberg.org/ebooks/11
;;
;;   PDF covering diphthongs and vowel combos that was helpful in counting syllables
;;      https://www.waikato.ac.nz/__data/assets/pdf_file/0005/314456/Word-lists-for-Vowels-Diphthongs.pdf
;;   PDF describing one particularly programatic syllable-counting method
;;      https://www.howmanysyllables.com/syllable_rules/howtocountsyllables
;;   Presentation showing how to identify silent E's
;;      https://ckla.amplify.com/skillsboost/wp-content/uploads/2020/08/G3_TeacherExtension_W1_D4.pdf
;;   Observation that I only had four parts of speech.
;;      SamR

Questions

Racket questions

Reading questions

When using struct do we ever have to use define or does struct serve as the definition?

struct implicitly defines all the procedures (the constructor, the basic predicate, the extractors, mutators if we permit them, etc.)

Can you summarize the main idea in the precondition testing reading?

Sometimes programmers provide incorrect parameters to the procedures we create. We may want to issue an error when that happens. We can use the error procedure to do that.

Why didn’t you have us do preconditions earlier?

Um … I’m not sure.

Why would I create a new data type when I could just put data in a pre-existing structure like lists, vectors or hash-tables?

Data abstraction! This takes us further along the path that “the implementation doesn’t/shouldn’t matter”.

It’s less work to write (struct foo (a b c)) than to write the five procedures that command generates.

Data protection / program safety. Client programmers can’t do things with our structures other than what we permit. (More or less.) If you use a hash table or a vector, clients might be able to mutate them when we don’t want them to.

Other issues

Do you plan to distribute grade reports soon?

Yes; sometime this weekend.

I like CS. What should I take next year.

CSC-161, Imperative Problem Solving, is the next course in our introductory sequence.

CSC-207, Objects, Data Structures, and Algorithms, follows 161.

If you are considering a CS major, you might also look toward MAT/CSC-208 or MAT-218, which provide the mathematical foundations of CS. (Taking one of the two is required for the major.)

Lab

Preparation

• Have the normal start-of-lab discussion.
• There’s an extra file to download.

During Lab

Exercise 4: Sam screwed up. Please add (require (file "date.rkt")) to the top of your file. (There’s a built-in date type with ten fields; we’re replacing that one.)

Wrapup

; SAM SAID I COULD STOP HERE