Held: Tuesday, 18 February 2014

Back to Outline 17 - Exam 1 Discussion. On to Outline 19 - Conditionals.

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) (PDF)

Overview

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

Administrivia

• Reading for Tuesday: Conditionals
• I apologize for the problems in MathLAN. (They are not my facult, but I do worry that they affect your ability to get work done.)
  • I have made HW 4 optional.
• I have virtual computers for 151 that you can run on your own computer.
  • Get a flash drive from Ajuna.
  • See instructions at https://github.com/GlimmerLabs/virtual-mediascheme/blob/master/UserGuide.md
• Extra credit:
  • Thursday extra: Technical Interviews.
  • Friday CS Table: Skip Lists.
  • Improv Saturday.

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!