CSC 151.01, Class 28: Higher-order procedures, revisited

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Questions
• Trees lab, continued
• Quick debrief
• Vectors lab
• Debrief (?)

Preliminaries

News / Etc.

• Continue partners!
• Quiz 9 returned. We’ll talk about it quickly.
• I finally got my grading software re-written. Expect email grades later today. Feel free to send corrections.
  • The math could be wrong.
  • I could be missing grades (e.g. extra credit)

Upcoming work

• Exam 3
  • Exam due TOMORROW via email
  • Epilogue due Wednesday via email
  • Cover sheet due in class Wednesday
• Lab writeup for class 27/Trees: Exercise 8. Due before class Wednesday.
• Lab writeup for class 28/HOP: Exercise 5. Due before class Wednesday.
• Reading for Wednesday
  • Files in Scheme
• Flash Cards due Wednesday at 5pm.
  • Optional.
  • Percent of eight flashcard assignments you complete (capped at 100).

Extra credit (Academic/Artistic)

• Mando Memorial Lecture, Tuesday at 4:15 p.m. in JRC 101

Extra credit (Peer)

• Drag show April 14

Extra credit (Recurring peer)

• Listen to KDIC Wednesdays at 6pm - Witty banter with other personalities and/or co-host. Also Indian, Arabic, and Farsi music.
  (Up to two units of extra credit.)
• Peer editing with SS. Talk to SS about the details. Make your English Lit more literate.

Extra credit (Misc)

• Host one or more prospective students. (I think there’s one visit weekend left.)

Other good things

• Leah Lakshmi Piepzna-Samarashina talk tonight at 7:30 p.m. in Harris.
• Tom Jorling presentation 7:30 p.m. tonight in Noyce 2022
• Movie: Making a Killing: Guns, Greed and the NRA, Tuesday, 7pm

Questions

Should we do more than just run your test suite in the examples section?

I’d prefer that you either (a) add a test case or two or (b) run an extra example or two by hand.

You do, however, have to show the result of running run-tests.

Can we convert lists to vectors in exam 3?

No.

Continue trees lab

Writeup: Exercise 8, number-tree-sum.

Start hop lab

How does apply differ from map?

• map applies a procedure to each element of a list, creating a list of new values.
• apply applies the procedure to all the elements en masse, creating on value of whatever type the procedure returns.

How does apply differ from reduce?

• reduce reduces a list to a single value by repeatedly applying it to neighboring pairs. (reduce + '(1 2 3 4)) is approximately (+ (+ (+ 1 2) 3) 4)
• apply does everything en masse. (apply + ‘(1 2 3 4)) is (+ 1 2 3 4)`
• reduce needs to have a binary procedure that returns the same type that it takes as input.
• In contrast, apply can return different types (and even take different types of inputs).
  • We can’t write (reduce < '(1 2 3 4)). (Why not?)
  • We can write (apply < '(1 2 3 4)). That computes (< 1 2 3 4).
• We can use apply in a variety of other situations, such as with ternary procedures.
  • We can’t write (reduce substring '("grinnell" 0 4)).
  • We can write (apply substring '("grinnell" 0 4)).

What’s the writeup for class 28?

• Exercise 5. Solve with recursion.

Debrief on trees lab

Next class.

Writing number-tree-largest.

Debrief on hop lab

Next class.

Direct recursion is your friend!