Class 22: Revisiting Lists

Held: Tuesday, 28 February 2017

We consider more general approaches to lists in Scheme

Preliminaries

Overview

• Lists, revisited
• car, cons, and cdr
• Other new list operations
• Representing drawings as values

Related Pages

• Eboard 22 (Source)

• Reading: Building Data Structures with Heterogeneous Lists

• Lab: Exploring Lists

Updates

News / Etc.

• Continue partners!
• While our lab grader seems to be on top of things, our homework grader seems to be having trouble keeping up. I’m looking to hire an additional homework grader. I apologize for the difficulties. I hope things will be resolved soon.
• Strike policy reminder. I respect the student initiative on this issue. But you should have something to strike against. I will still teach class. I will not penalize you for missing class if you send me a one-paragraph reflection on some aspect of the strike.

Rotating reminders

• Visit me in my office! I’m always happy to see students during my office hours. I prefer that you book me at https://rebelsky.youcanbook.me, but you can also just show up during office hours and hope that I’m not busy.
• Note that my office hours have been filling as of late. Talk to me individually if you can’t find a booking time.

Upcoming Work

• Assignment 5 due TONIGHT at 10:30 p.m.
• Lab writeup: TBD
• Reading: Recursion basics
• Exam 2 arrives tomorrow.

Extra credit (Academic/Artistic)

• CS Table, Tuesday at noon: Facial Recognition “algorithms”
• W. Kamau Bell, Tuesday at 6pm, Harris.
• Prazak Quartet, Tuesday, 28 February 2017, 7:30 p.m., Herrick.
• CS Extras, Thursday at 4:15 pm, Sam’s research and PM’s research

Extra credit (Peer)

Extra credit (Misc)

• Non-violent protest training session TODAY at 4:00 in JRC 101.
• Preventing sexual assault, Tuesday at 11am, JRC 101
• Host a prospective student THIS COMING WEEKEND. (March 5, April 8, April 23)
• Write the eboard equivalent for class Tuesday, Wednesday, or Friday next week.

Good things to do

• Bagel party in Math commons, Thursday, 7-9 pm. Lox status unclear.

Lists

• Our first encounters with lists.
  • Collection of values
  • Homogeneous: All the values in a list are the same type
  • Used primarily with map
• Extending that notion
  • Can also be heterogeneous: Values in the list may have multiple types.
  • Can examine individual elements with car, cdr, and list-ref.
  • Can be extended (creating new lists) with cons.
  • There’s an empty list: null.
• Why is the new view important?
  • It will soon give us the opportunity to manipulate lists in new and interesting ways.

Implementing Drawings

• We can (and do) use lists to implement drawings.
• The reading considers a simplified representation, in which the width and height of a drawing are the same.
• But the general process is the same
  • Group the values in a list
  • When we need to render or manipulate a drawing, use the list operations to extract parts.

Lab