Overview

• Preliminaries.
  • Admin.
  • Upcoming work.
  • Pre-quiz Questions.
  • Quiz.
• Topics.
  • Why name things.
  • Naming things with let.
  • Naming things with let*.
  • Naming procedures.
• Lab.

Preliminaries

Admin

• Extra credit:
  • Improv Saturday 9 at Loose.
  • Tuesday Town Hall noon and 7pm.
  • Thursday CS Extras: New CS Curriculum.

Upcoming Work.

• Reading for Monday: Anonymous Procedures
• Writeup: Exercises 6d and 7b
  • Subject: CSC 151.02 Writeup 13: Let (OPTIONAL NAMES)
• Homework 5 is ready. Pick your own groups.

Pre-quiz Questions

What are the differences between if and cond?

If asks you to choose between two options, cond lets you do as many as you want.

Nesting ifs lets you achieve the "as many as you want

(if (test1)
    consequent1
    (if (test2)
        consequent2
        (if (test3)
            consequent3
            alternate)))

(cond
  [(test1) consequent1]
  [(test2) consequent2]
  [(test3) consequent3]
  [else alternate])

For choosing between two things, most people find the if easier. For more than two choices, most people find cond easier.

Another advantage to cond: Multiple consequents

(cond
  [(test1) consequent1a consequent1b]
  [(test2) consequent2a consequent2b consequent2c]
  [(test3) consequent3]
  [else alternate])

When is when you have one test, several consequents, no alternate.

Quiz

Lab

Note: Scheme likes parentheses, so

(let ((NAME VAL))
  EXP)

Alternately

(let ([NAME VAL])
  EXP)