CSC 151.01, Class 04: Introducing lists

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Questions
• Lab
• Debrief

Preliminaries

News / Etc.

• Welcome back to our permanent version of Shelby.
• Thanks for keeping the room neat.
• When you speak in class, please say your name first.
• I’m already behind on grading. I apologize.
• I talk fast. I try to slow myself down by writing a lot. But it could can be difficult. Question for you (I’ll close my eyes for the answer): How is my speed?
  • Please try to slow down a bit.
  • It’s fine, or at least acceptable.
  • Please try to speed up.

Upcoming work

• Assignment 2 due TOMORROW night.
• Readings (online), due before class Wednesday.
  • Defining your own procedures
  • How Scheme evaluates expressions, take 2
• Lab writeup for class 4, due before class Wednesday
  • Exercise 6.
  • “CSC 151.01 Writeup for Class 4 (Your Name)”
  • Mail to csc151-01-grader@grinnell.edu
• Flash cards due at 5pm Wednesday.
  • See below for additional details.
  • Submit ten flash card Q&As via email with a subject of “CSC 151.01 Flashcards (Week 2)”

About flash cards

• A chance to summarize some key points or confusing points.
• A potential study mechanism.
• Both aspects have documented effect on learning basic concepts.
  • And you can’t do the complex stuff in CSC 151 unless you know the “language”: vocabulary, syntax, etc.
• Examples:
  • What is (round 3.4)?
  • How does 1/2 differ from 0.5?
  • How does 1/2 differ from (/ 1 2)?
  • What are the parameters to substring?
  • What is (substring "Hello" 1 3)?
• Answers:
  • 3.0
  • 1/2 is exact; 0.5 is inexact.
  • 1/2 represents a number. (/ 1 2) represents a computation.
  • (substring string start-pos after-end-pos)
  • "el"
• I will provide you with a summary of the questions and answers.
• You may use them in whatever way you consider best.
• Usually about a week’s worth of work (WFMW)

Extra credit (Academic/Artistic)

Extra credit (Peer)

• Posse Plus Retreat Recap, February 6 at 11am, JRC 101.

Extra credit (Misc)

Other good things

Questions

Why do you write some strange symbols, such as backticks, when you write the eboards?

I use a “language” called Markdown to format my text; it allows me to make the “pretty” Web pages without too much effort.

Why am I getting stupid errors from map1, like “that’s not an integer”, when it is?

Sam needs examples.

I want to do the self-checks on my own computer. What do I do?

Download DrRacket. (Free.)

Add the CSC151 package. (See day 1 lab.)

Email me an example of it not working.

Can I do without the (require csc151).

Probably, but I don’t know what it is.

How should we separate the different examples in HW 1?

In a way you think it will be easy for the grader to understand.

Is there a citation format you prefer?

I like APA.

I care more about the act of citing than the precise format. A URL suffices.

Lab

Note: You can comment stuff out by surrounding it with pound-bar and bar-pound.

#|
Look, DrRacket will ignore this.  So I can type incorrect stuff
(3 + 4), examples, and more.
|#

Keyboard shortcuts

• Ctrl-up - Previous command
• Esc-p - Previous command
• Ctrl-down - Next command

Debrief

• Which of the following is easier for you to do: count the number of elements of a list by hand or write (length lst)? Take advantage of what the computer can do!
  • Using length can also lead to more general solutions.
• I’m happy to see that some of you are checking the answers (e.g., on the calculator you carry with you).
  • I wrote reduce. You’ve already seen that I sometimes lack competenence (e.g., in building Web sites). I could have written an incorrect definition of reduce.
• There are at least three ways to add 2 to each element of a list.
  • (map increment (map increment lst))
  • (map (o increment increment) lst)
  • (map + lst (make-list (length lst) 2))
• Some of you are already encountering the issue of “I should be able to write this, but I can’t.” Welcome to working within limits.
• You will learn better ways to write things like “add 1.5” in the next lab.

A solution to problem 5

(map min
     (make-list (length ratings) 6)
     (map max
          (make-list (length ratings) 0)
          ratings))

Theme of next few weeks: What we can do with individual values, we can do with lists of values.