Class 07: Procedure Definitions

Held Tuesday, September 10, 2002

Summary

Today we begin to consider how you can write your own procedures.

Assignments

• Read Boolean values.
• Read Conditionals.

Notes

• Are there any questions on homework 1?
• Reese will have office hours tonight (and every Tuesday) from about 9:00 to 10:00 p.m.
• I'll be holding a lab in MathLAN from 2:15-3:05 today. Feel free to stop by and ask me questions.
  • I might also be available after 3:05. If you want to talk to me, please let me know.
• I finally picked up a coffee pot, so we'll have coffee in class starting today. Please be careful with the coffee!

Overview

• Why define your own procedures?
• How to define your own procedures
• Lab

User Defined Procedures

• It's clear that programmers often want to (and need to) define their own procedures.
• User-defined procedures can add clarity to a program.
  • Rather than looking at how code does something, the user of a procedure can focus on what the code does.
• Programmers can avoid repetitive (and, therefore, error prone) code.
  • Rather than retyping the same code again and again, just changing a few values, a programmer can give a name to the same code.
• How do you define your own procedures? Using the following template:

  (define your-procedure
    (lambda (param1 ... paramn)
      expression-possibly-involving-parameters))
  

• For example,

  (define square
    (lambda (val)
      (* val val)))
  

• You can (and should) document your procedures so that others can understand what they are supposed to do.

Lab on User-Defined Procedures

• Do the lab.
• Be prepared to reflect (e.g., to describe the most important or most confusing thing you dealt with today).