Held: Friday, 26 September 2014

Back to Outline 16 - Homogeneous Lists: Making and Manipulating Groups of Drawings . On to Outline 18 - Programming the GIMP Tools.

Summary

We consider the ways in which Scheme supports yes/no questions and procedures that can be used to ask such questions. We also see how such procedures can provide another form of control.

Related Pages

• Reading: Boolean Values and Predicate Procedures
• Lab: Boolean Values and Predicate Procedures
• EBoard (Source) (HTML)

Overview

• Boolean values.
• Predicates - Procedures that return Boolean values.
• Combining booleans with and and or.

Administrivia

• New lab partners!
• Office hours: Today, 1:45-3:15; Also walking hours 1:15-1:45. Monday's hours are distorted by prospective student events. I'll try to stay around later in the day than normal.
• Let me know by Monday if you want to work alone on HW 5.
• A few of you have said that you cannot sign the second academic honesty statement. I am currently debating what to do next. If you have suggestions, send them anonymously on the questions page.
• It's Friday. I hope you have a chance to restore this weekend.
  Please be thoughtful about your choices this weekend (and not just because there are lots of families on campus).

Upcoming Work

• No lab writeup today (no matter what it says online).
• Reading for Monday:
  • The GNU Image Manipulation Program
  • Programming the GIMP Tools

Extra Credit Opportunities

Academic

• CS Table today: Privacy and Big Data in the Social Sciences
• Campus Town Hall September 30 t 7:30 p.m.
• CS extras next Thursday: Alumni
• CS table next Friday: Serendipity and Computing (with Grinnell's Artist in Residence)
• Grinnell Prize events the following week (particularly events related to the prize winners whose project involves Web tools)

Peer Support

• Science poster session, Sat., Sept. 27, morningish, science elbow
• Football Games (Saturday, Sept. 27, at 1pm)
• Noteworthy, Sat., Sept. 27, 3:30 p.m. Herrick
• Men's Tennis (???)
• Women's Tennis (???)
• Swimming (???)
• Anna Christie, Oct. 9-12 (SB plays Marthy)
• Evan's radio show 5pm Friday nights on KDIC
• Donna's radio show Sunday midnight on KDIC

Miscellaneous

• Participate in #GrinWell. http://www.grinnell.edu/forms/sign-grinwell-presidents-wellness-challenge
• Friends of Drake Library needs help setting up for their annual booksale on Thursday, October 2 (conveniently, the same night as Grinnell High School's homecoming parade). You can help a good cause and probably get a few free books, too.
  • Update: They can also use help on Wednesday, October 1.

Preparation

• What did you learn from the reading? (Let's try to summarize for each other.)
• What questions do you have?

or and and as control structures

• How does normal procedure application work?
  • Evaluate all the parameters
  • "Plug them in to the body"
  • Evaluate the body
• How does or work?
  • It evaluates each parameter, in turn, until one holds (or it runs out of parameters).
  • As soon as one holds, it stops and returns that value.
• How does and work?
  • It evaluates each parameter, in turn, until one fails to hold (or it runs out of parameters).
  • As soon as one fails to hold, it stops and returns #f.
• This evaluation strategy means that we can use and and or to evaluate a sequence of expressions, stopping when we get the first acceptable one.

Lab

• Work on the lab
• Be prepared to discuss!