New partners!

• Grab a card from the stack.
• Identify the location of the new computer.
• Drop the card in the jar.
• When both of you are at the computer, introduce yourselves.

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Review.
• Procedures with Lambda Expressions.
• Lab.

Preliminaries

Admin

• Mentor sessions Wednesday and Thursday at 8pm in the Commons.
• Sam review session Thursday at 10am in our classroom.
• We'll spend the start of class going over some of the key ideas from the past week. I hope you've brought lots of questions.
• On Friday, I will discuss mechanisms for working on CSC 151 outside of Noyce. (Or at least I'll distribute instructions.)
• Today's lab will continue into Friday's class.

Upcoming Work

• Review today's readings for Friday: Procedures How Scheme Evaluates Expressions (take 2)
• Assignment 3 due Tuesday @ 10:30 p.m.
  • Your partner is the person who you are working with today and Friday.
• Quiz Friday!
  • RGB Colors, including functions on RGB colors
  • Basic image functions
  • Composition with o
  • Sectioning with section
  • Plus Scheme basics
  • No lambdas
• Lab writeup (due before class Monday)
  • Email to grader-151-01@cs.grinnell.edu
  • Subject: CSC 151 Lab Writeup Class 8 (Your Names)
  • Exercise: 1

Extra Credit Opportunities

Academic

• Don't Forget Convocation Tomorrow! Convocation, Thursday, 11am, JRC 101, Global Health.
• CS Extra tomorrow at 4:15 in Science 3821 on System Administration
• Tuesday, noon, CS Table, JRC 224C. Hacking Cars.

Peer Support

• Pals of PALS, pals@grinnell.edu, normally Saturday at 1:30 and Mondays at 4:45. Requires sign up in advance.
• Pun Club, Saturdays, 4pm, Way over Younker.
• Singers concert on Family weekend! Sept. 26, 2pm., JRC 101
• Orchestra concert on Family weekend! Sept. 26, 2pm., place TBD (S-L)
• Les Duke on Saturday. Peers running at 10:45ish, but any time is okay (30 min min)
• Public events series Abraham in Motion Sat at 7:30. TICKETS NEEDED! Bucksbaum box office.

Questions

Review

• What are the components of algorithms?
• Which of those have we learned to do in Scheme?
• What other questions do you have about what we've covered so far? Write them on cards, one question per card.

Components of algorithms

• Variables - Values that we can store; we name/define them ourselves We can do this in Scheme with (define NAME VALUE) or (define NAME EXPRESSION). In the definitions pane. Also in the interactions pane, but those are less permanent.
• Parameters - Inputs to our algorithms (or to subroutines). (We're just starting to think about how to do this.)
• Subroutines - Things that will be done; named algorithms that contribute to our broader algorithm. We can write these as expressions Use define again! (E.g., (define square (lambda (x) (* x x)))) Parameters appear after the lambda.
  • You can use whatever name you want

    (define ave2 (lambda (x y) (* 1/2 (+ x y)))) (ave2 10 20) 15 (ave2 80 -50) 15 (define ave2 (lambda (x y) 15)) (ave2 100 5) 15

  • Can we write subroutines without using lambdas? Yes! Using section. (define add2 (section + <> 2)) Also with o. (define fun (o square increment)) - function that adds one and then squares.
  • Maybe by putting the steps in a file and then loading the file.
• Repetition - Write the same instructions again and again and again image-variant does repetition - it applies a color transform to every color/pixel in an image. Still need to learn more.
• Conditional - Like the "if then" things - making choices. Still need to learn.
• Sequencing. Parentheses plus inside-out evaluation. Write a series of expressions; it does the first then the second then the third In experessions like (- (square 5) (square 4)), the squares get done before the subtract, but we don't know which square gets done first and it shouldn't matter. Composition also creates a series of things to do (
• Basic operations and values: Math, RGB colors, ... Vocabulary!

Writing Procedures with Lambda

• What questions do you have about the reading?

Lab