Held: Monday, 21 September 2015

Back to Outline 13 - Testing Your Procedures, Revisited. On to Outline 15 - Drawings as Values.

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 14 (Source 14)

Overview

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

Administrivia

• 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.
• Review sessions:
  • Wednesday, 8pm (mentor)
  • Thursday, 10am (Sam)
  • Thursday, 8pm (mentor)
• I graded all of the lab 12 and lab 13 writeups I had received by 8pm on Sunday night. The rest will be graded significantly later.

Upcoming Work

• Reading for Tuesday Drawings as Values
• Exam 1
  • Electronic due Tuesday: http://bit.ly/151-2015F-exam1
  • Epilogue due Tuesday http://bit.ly/151-2015F-exam1epi
  • Printed version due Wednesday
• Today's Lab writeup (due before class Monday)
  • Email to grader-151-01@cs.grinnell.edu
  • Subject: CSC 151 Lab Writeup Class 14 (Your Names)
  • Exercise:

Extra Credit Opportunities

• I remain a little behind in responding to these. Sorry!

Academic

• Any visit to the current show in the Faulconer gallery
• John Gerrard talk, "Corn Bomb", tonight at 8pm
• No CS Table this week - It's advising week!
• Wednesday CS Extra this week, 4:15 in 3821: Ursula Woltz on Building Coding Communities
• Thursday CS Extra this Week, 4:15 in 3821: SamR on The Architecture of Mediascript

Peer Support

• Pals of PALS, pals@grinnell.edu, normally Saturday at 7:45 am (breakfast included), Sunday at 4:45, 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., Sebring-Lewis
• Orchestra concert on Family weekend! Sept. 26, 2pm., Sebring-Lewis

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!