Class 07: Procedure Definitions

Held Thursday, February 1, 2001

Summary

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

Assignments

• Read Boolean values.
• Read Conditionals.

Notes

• Tutoring will be available Sunday through Thursday nights from 9:00-10:00 p.m. in the Computer Equipped Classroom (Science 2435).
  • John Emmons Sundays
  • Anne Feltovich Mondays
  • Greg Fuller Tuesdays
  • Ming Gu Wednesdays
  • Anne Feltovich Thursdays
• While personal tutors are also available for CS151, I'd prefer that you wait until after the first exam to ask for a tutor.
• Reminder: homework 1 is due tomorrow at the start of class.
• A few of you have asked me about what you'll be expected to do for labs. I'll assign a few required lab questions each week (after you've completed the labs) and ask you to turn them in a few days later.
• I've slightly rearranged the schedule so that you don't have a reading due this weekend. We'll finish the procedures lab and the conditionals lab on Monday (along with discussing any pitfalls you've encountered).
• Grinnell Entrepreneurs is hosting a conference on Entrepreneurship on Saturday, Feb. 17. Although the literature doesn't say so anywhere, it's free for Grinnell students. More info is available at http://www.grinnell.edu/groups/ge.

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)))
  

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).