Programming in Alice

357 Pages·2003·22.55 MB·English

Preface to the Instructor...............................................................................................................x
1 Introduction.................................................................................................................................1
Why Learn about Programming Computers?..........................................................................1
How You Will Learn to Program with This Book and Alice..................................................2
The Basics of Computer Programming...................................................................................3
Why is it called Alice?.............................................................................................................4
1 Alice............................................................................................................................................15
What is a Virtual World?.......................................................................................................15
How does Alice create an animation?...................................................................................16
An Alice virtual world...........................................................................................................16
3D Models of Objects............................................................................................................17
Tutorials.................................................................................................................................19
1 Exercises.............................................................................................................................19
Tips & Techniques 1....................................................................................................................22
Window size..........................................................................................................................22
Arranging objects...................................................................................................................22
Moving subparts of objects....................................................................................................23
A comparison of motions.......................................................................................................24
Vehicle...................................................................................................................................24
3D Text..................................................................................................................................26
2 Programming in Alice: Design and Implementation............................................................50
2-1 Scenarios and Storyboards (Design)...................................................................................51
Visual Storyboard..................................................................................................................52
Generic Template...................................................................................................................53
2-2 A First Program...................................................................................................................59
What is a Program?................................................................................................................59
2 Summary.................................................................................................................................71
Tips & Techniques 2....................................................................................................................72
Style.......................................................................................................................................72
Sound.....................................................................................................................................72
point at and onlyAffectYaw...................................................................................................74
Clipboards..............................................................................................................................76
As seen by..............................................................................................................................77
3 Methods and Parameters .......................................................................................................100
3-1 Methods: World-level........................................................................................................101
Methods...............................................................................................................................101
Why do you care?................................................................................................................101
Example...............................................................................................................................101
Creating our own method....................................................................................................102
Calling (Invoking) a Method...............................................................................................104
Comments............................................................................................................................106
Technical Note.....................................................................................................................107
3-1 Exercises........................................................................................................................108
3-2 Parameters.........................................................................................................................110
Example...............................................................................................................................110
Setting the Stage ..................................................................................................................110
Storyboard with a Parameter...............................................................................................111
Creating an Object Parameter..............................................................................................112
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Using an Object Parameter..................................................................................................113
Importance of Parameter Type............................................................................................115
Test with Arguments............................................................................................................116
Multiple Parameters.............................................................................................................117
Other types of parameters....................................................................................................121
Example...............................................................................................................................121
Number parameter...............................................................................................................122
Technical Note.....................................................................................................................122
3-2 Exercises........................................................................................................................124
3 Summary...............................................................................................................................126
3 Projects.................................................................................................................................127
Tips & Techniques 3..................................................................................................................131
Renaming an Object............................................................................................................131
Color Property as Identification...........................................................................................131
Printing your program code.................................................................................................133
Orient to...............................................................................................................................133
4 Character-Level Methods and Inheritance..........................................................................150
4-1 Creating New Characters...................................................................................................151
Example...............................................................................................................................151
A Character-Level Method..................................................................................................151
A Second Example..............................................................................................................154
Saving a New Character......................................................................................................156
Inheritance...........................................................................................................................157
Benefits: reuse and teamwork..............................................................................................157
Guidelines for Writing Character-level Methods................................................................157
Character-level Method With an Object Parameter.............................................................159
4-1 Exercises........................................................................................................................160
4 Summary...............................................................................................................................162
4 Projects.................................................................................................................................163
Tips & Techniques 4..................................................................................................................164
Properties.............................................................................................................................164
Setting Properties at Runtime..............................................................................................164
Built-in Questions (Functions)............................................................................................168
Collision...............................................................................................................................171
Expressions..........................................................................................................................171
The move to instruction.......................................................................................................173
5 Interactive Programs: Events and Event-Handling...........................................................200
5-1 Interactive Programming: Events and Event-Handlers.....................................................201
Input.....................................................................................................................................202
Design -- Storyboards..........................................................................................................202
Event-handler methods........................................................................................................203
Link Events to Event-handlers.............................................................................................203
Testing.................................................................................................................................205
Technical Notes...................................................................................................................205
Mouse-Control Example......................................................................................................207
Design -- Storyboards..........................................................................................................207
Event-handler methods........................................................................................................208
Link Events to Event-handlers.............................................................................................208
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Technical Note.....................................................................................................................210
5-1 Exercises........................................................................................................................211
5-2 Passing Parameters to Event-Handlers..............................................................................214
Numeric parameter example................................................................................................214
Design -- storyboard............................................................................................................214
Three events, one event-handler..........................................................................................215
Parameter is used for both duration and distance................................................................215
Link events to event-handler...............................................................................................216
Pass a number parameter.....................................................................................................216
Testing.................................................................................................................................217
Object parameter example...................................................................................................217
Design -- Storyboard............................................................................................................218
Writing the event-handler....................................................................................................218
Link the event to the event-handler.....................................................................................220
Testing the program.............................................................................................................221
Technical Notes...................................................................................................................221
5-2 Exercises........................................................................................................................223
5 Summary...............................................................................................................................225
5 Projects.................................................................................................................................226
Tips & Techniques 5..................................................................................................................229
Let the mouse move objects................................................................................................229
Billboards.............................................................................................................................230
Special Effect: fog...............................................................................................................231
Rotating around an invisible object.....................................................................................233
6 Decisions and User-defined Questions................................................................................250
6-1 Decisions and Logical Questions......................................................................................251
Decisions..............................................................................................................................251
If/Else Example...................................................................................................................251
Logical Operators................................................................................................................254
Nesting If statements............................................................................................................257
Else......................................................................................................................................257
Relational operators.............................................................................................................257
6-1 Exercises........................................................................................................................259
6- 2 User-defined Questions I (Boolean).................................................................................262
Introduction to Questions....................................................................................................262
Abstraction...........................................................................................................................262
User-defined questions ........................................................................................................262
Creating a new Question......................................................................................................263
Calling the question.............................................................................................................265
A more complex Boolean question......................................................................................265
6-2 Exercises........................................................................................................................268
6-3 User-defined Questions II (Number).................................................................................271
Other types of questions ......................................................................................................271
User-defined number question.............................................................................................271
Testing.................................................................................................................................274
Using a question with a relational operator.........................................................................274
Abstracting a character-level method..................................................................................275
World-level question for generic use...................................................................................275
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6-3 Exercises........................................................................................................................277
6 Summary...............................................................................................................................279
6 Projects.................................................................................................................................280
Tips & Techniques 6..................................................................................................................284
If/Else and visibility as a condition.....................................................................................284
Camera: View from the back...............................................................................................285
Lighting up the rear view.....................................................................................................287
7 Repetition: A Counted Loop.................................................................................................300
7-1 Loops................................................................................................................................301
Introducing repetition..........................................................................................................301
The need for repetition.........................................................................................................301
Using a Loop........................................................................................................................303
Count....................................................................................................................................304
Loops and Do in order or Do together.................................................................................304
Technical note on looping...................................................................................................306
7-1 Exercises............................................................................................................................307
7 Summary..............................................................................................................................309
7 Projects.................................................................................................................................310
8 Repetition: Recursion............................................................................................................350
8-1 Repetition: Random motion and recursion........................................................................351
Introduction..........................................................................................................................351
Chase scene..........................................................................................................................351
Unknown number of repetitions..........................................................................................351
Random motion...................................................................................................................353
Recursion.............................................................................................................................356
8-1 Exercises........................................................................................................................359
8-2 Structural Recursion..........................................................................................................361
A closer look at generative recursion..................................................................................361
Structural recursion..............................................................................................................361
Towers of Hanoi puzzle.......................................................................................................361
Towers Method....................................................................................................................363
Conversion Question...........................................................................................................366
Exercise:..............................................................................................................................368
8 Summary...............................................................................................................................369
8 Projects.................................................................................................................................370
9 Repetition: While Statements................................................................................................400
9- 1 While ................................................................................................................................401
Revisiting the Chase............................................................................................................401
Using while..........................................................................................................................402
A game-like example...........................................................................................................403
How to determine when the race is over.............................................................................404
Random selection.................................................................................................................405
9-1 Exercises........................................................................................................................407
9-2 Infinite Repetition..............................................................................................................408
Mutually invoked methods..................................................................................................408
Infinite recursion..................................................................................................................410
Infinite Loop and while statements......................................................................................411
9-2 Exercises........................................................................................................................414
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9 Summary...............................................................................................................................417
9 Projects.................................................................................................................................418
10 Lists and List Processing......................................................................................................450
10-1 Lists.................................................................................................................................451
Creating a list.......................................................................................................................451
For all in order -- Iterating sequentially through a list.........................................................453
For all together -- Iterating simultaneously.........................................................................455
10-1 Exercises......................................................................................................................457
10-2 List Search.......................................................................................................................461
Simulation using a list search..............................................................................................461
First Subtask – Game in progress........................................................................................463
Second Subtask – Scoring ...................................................................................................464
10 Summary.............................................................................................................................466
10 Projects...............................................................................................................................467
11 Arrays....................................................................................................................................500
11- 1 Arrays: Creation and use................................................................................................501
Introduction to arrays...........................................................................................................501
Creating an array..................................................................................................................501
Accessing an element in an array........................................................................................501
Iterating though an array to find an element with a certain property..................................502
Searching through an array to find the tallest element ........................................................504
Using a location index variable a while statement in place of an iterator...........................507
11 Exercises.........................................................................................................................509
11- 2 Sorting arrays.................................................................................................................510
What is sorting?...................................................................................................................510
Insertion sort........................................................................................................................510
Walk through the array........................................................................................................511
Remove an element from the array......................................................................................511
Insert element in its correct location....................................................................................512
11-2 Exercises......................................................................................................................517
11 Summary.............................................................................................................................518
11 Projects...............................................................................................................................519
12 Revisiting Inheritance: Mutable variables.........................................................................550
12 -1 Inheritance......................................................................................................................551
Character-level variables.....................................................................................................551
Using a character-level method to track steering a car........................................................551
Figure 12-1-1. An initial scene............................................................................................551
Implementation....................................................................................................................552
12-1 Exercises......................................................................................................................559
12 Summary.............................................................................................................................562
13 Cool Worlds You Can Build................................................................................................600
13-1 Cool worlds.....................................................................................................................601
A flight simulator.................................................................................................................601
Initial world with billboard instructions..............................................................................601
Planning the simulation.......................................................................................................601
How do we know when the plane is flying through a ring?................................................602
When should the game end?................................................................................................603
What happens if the plane flies into the ground?................................................................605
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How do we start the game, continue to fly the plane, and keep track of the game?............607
How does the user steer the plane?......................................................................................608
13 Exercises.........................................................................................................................611
14 Transition to Real World Languages..................................................................................612
14-1 Transition to Java/C++: Syntax Switch...........................................................................613
Syntax..................................................................................................................................613
14-2: Objects and Classes........................................................................................................618
Objects.................................................................................................................................618
Classes.................................................................................................................................619
Creating (instantiating) objects............................................................................................620
“What you see is what you get”...........................................................................................621
Creating new classes............................................................................................................623
Encapsulation.......................................................................................................................624
Data Types and Structures...................................................................................................625
Methods and Functions (Questions)....................................................................................625
14-3: Program Constructs........................................................................................................322
Do in order and Do together ...............................................................................................322
Decision-making..................................................................................................................322
Repetition: loop (for)...........................................................................................................323
Repetition: while..................................................................................................................324
Repetition: recursion............................................................................................................324
14 Summary.............................................................................................................................629
Appendix A.................................................................................................................................650
Alice Tutorial 1-1....................................................................................................................650
How to Start Alice:..............................................................................................................650
World 1: Opening and Running Your First World..............................................................652
World 2: Interactive World..................................................................................................655
World 3: All About Character Objects................................................................................656
Optional: Using the Web Gallery.......................................................................................657
Moving Objects...................................................................................................................658
Arranging Multiple Character Objects (the quad view)......................................................659
Moving the Camera.............................................................................................................662
Saving a World ....................................................................................................................663
Alice Tutorial 1 - 2..................................................................................................................665
Using One-shot Instructions To Position Objects...............................................................665
Using One-Shot Instructions to Say Text............................................................................671
Using One-Shot Property Animations.................................................................................672
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Preface to the Instructor

This book takes a radically different approach to teaching introductory programming.

There have been relatively few innovations in the teaching of programming in the last 30 years,
despite the fact that introductory programming courses are often extremely frustrating to
students. This text, with the associated Alice system, is intended to take a novel approach. We
strongly recommend you see a live demonstration of the Alice system, or a videotape, before
evaluating this text. The Alice system is free; the system and videos are available at
www.alice.org .

What is different about our approach?
Our approach allows students to author on-screen movies and games, where the concept of an
"object" is made tangible via on-screen characters that populate a three-dimensional micro world.
Students create programs by dragging and dropping program elements (if/then statements, loops,
variables, etc.) in a mouse-based editor that prohibits syntax errors. The Alice system is a
powerful, modern programming environment that supports methods, functions, variables,
parameters, recursion, arrays, and events. We use this strong visual environment to support an
objects-first approach (described in the ACM and IEEE-CS Computing Curricula 2001 report)
with an early introduction to events. In Alice, every object is an object that students can visibly
see! We begin with objects in the very first chapter.

In our opinion, there are four primary obstacles to introductory programming:
1) The fragile mechanics, particularly syntax, of program creation
The Alice editing environment removes the frustration of syntax errors in program creation, and
allows students to develop an intuition for syntax, because every time a program element is
dragged into the editor, all valid "drop targets" are highlighted.
2) The inability to see the results of computation as the program runs
Although textual debuggers and variable watchers are better than nothing, the Alice approach
makes the state of the program inherently visible. In a sense, we offload the mental effort from
the student's cognitive system to his or her perceptual system. It is much easier for a student to
see that an object has moved backward instead of forward, as opposed to noticing that the "sum"
variable has been decremented, rather than incremented. Today's students are immersed in a
world where interactive, three-dimensional graphics are commonplace; we attempt to leverage
that fact without pandering to them.
3) The lack of motivation for programming
Many students take introductory programming courses only because they are required to do so.
Nothing will ever be more motivating than a stellar teacher, but the right environment can go a
long way. In pilot studies of classes using Alice, students do more optional exercises and are
more likely to take a second class in programming than control groups of students using
traditional tools. The most common request we received regarding earlier versions of Alice was
the ability to share creations with peers; we have added the ability to run Alice programs in a
WWW browser so students can post them on their web pages. Although we have seen increased
motivation for all students, we have seen especially encouraging results with under-represented
student groups, especially female students.
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4) The difficulty of understanding compound logic and learning design techniques to overcome it
The Alice environment physically encourages the creation of small methods and functions.
More importantly, the analogy of making a movie allows us to utilize the concept of a
storyboard, which students know is an established movie-making process. Since most students
cannot draw their storyboards, we encourage them to express their high level story concept in
short prose snippets, which are progressively refined, essentially designing through pseudo-code.

How to Use this Text
Of course, as the instructor, you should use this text as you best see fit! Below are four ways we
imagine the book being used, but you may discover additional ways of using this textbook:
1. As the only text in a semester-long, or short-course on programming. This would
allow students to build relatively complex (say, 300-line) programs by the end of the
semester or term. Such a course might be for non-majors who want to learn the concepts
behind programming without a need for transitioning to a real-world language.
Alternatively, this course can be used as a pre-CS1 course for students who would like to
be, or are considering, a computer science major but who lack previous programming
experience. In our NSF-supported study (NSF-#0126833), we found that students who
jump right into a rigorous CS1 course with little or no previous programming have an
extremely high attrition rate in CS1. The use of an Alice course as a pre-CS1 course has
significantly reduced the attrition rate of these students in our CS1 courses.
2. As the first portion of a traditional "Introduction to Programming" course, such as
CS1 Both Seymour Papert's Logo and Rich Pattis' Karel the Robot have been used this
way, and these systems have inspired us greatly. Unlike these systems, Alice is powerful
enough to support students for several semesters (for example, seniors majoring in
Computer Science at Carnegie Mellon routinely write 3,000 line programs in Alice).
However, many introductory programming courses must both teach concepts and also
prepare students to write programs in traditional languages, such as Java. By learning
Alice first, students are well acquainted with the fundamental concepts of programming,
and can quickly learn the specific syntax rules of a particular "real" language as a
transition. Our final chapter provides support for this transition, and the Alice
environment can ease the transition by displaying programs with a Java-like syntax, as
shown in the Figure Preface-1 below.
3. As the programming component of a "Computer Literacy" course. At many
schools, computer literacy courses attempt to give a broad introduction to computers
and/or "information technology" to non-majors. Many of these courses have removed
their programming component and are little more than extended laboratories on "office
productivity tools" such as spreadsheets and word processors. Alice has the potential to
return a gentle programming component to these computer literacy courses.
4. In a high school “Introduction to Programming” course. A course in Alice has great
potential for a high school environment, where a high-interest, highly-motivating
environment is a teacher’s best friend. This course could be a stand-alone course as a
preparation for college courses or as preparation for the College AP computing course.
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Figure Preface-1: Programs in Alice (top) can optionally be displayed with a Java-like syntax (bottom)

Structure of the Book
The text begins with an introduction motivating why students would want to write a computer
program and addressing their fears about programming. We then have a brief first chapter on the
basic concept of a three-dimensional virtual world. The text contains a traditional, paper-based
tutorial as an appendix, and the Alice system also includes an interactive software-based tutorial
that some students may prefer.

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The remaining chapters begin with overview and motivation of the chapter’s topic, have
exercises at the end of each section, and end with a summary. For your convenience, the
following is a (very) brief overview of the major concepts covered, chapter by chapter. Clearly,
the major focus of the text material is an introduction to the fundamental concepts of
programming.

Chapter 1 3D worlds, 3D models (classes) and objects in the worlds.
Chapter 2 Storyboard design and a first program.
Chapter 3 World-level (global) methods and parameters.
Chapter 4 Character-level methods and using inheritance to define new classes of
objects.
Chapter 5 Interactive programs: events and event-handling
Chapter 6 Decisions and user-defined questions (functions)
Chapter 7 Repetition: a Counted Loop (for)
Chapter 8 Repetition: Recursion
Chapter 9 Repetition: While statement
Chapter 10 Lists and List Processing
Chapter 11 Arrays
Chapter 12 Revisiting inheritance: mutable variables
Chapter 13 Cool Worlds You Can Build
Chapter 14 Transition to Real World Languages (Java/C++)

At the end of most chapters is a selection of larger, more free-form projects. We have found
projects to be an enjoyable and important part of our Alice courses. The projects provided in this
text are meant to inspire, not weigh down the student. In particular, we recommend “open-
ended” projects. An open-ended project asks students to design their own animation beginning
with their own storyline and using objects of their choosing. We do require that a project meet
certain requirements. For example: “…an interactive world, containing two or more interactions
with the mouse, at least three methods, and two characters you have created by writing character-
level methods and saving out the characters.” Alice lends itself particularly well to student
demonstrations of their worlds to the rest of the class on the project due date.

Following most chapters is a "Tips and Techniques" section for students who may be interested
in the fun features of Alice that we don’t cover as part of the fundamental concepts of
programming presented in the major chapter material. Use of the Alice interface is integrated
with examples for programming concepts, where needed. The Tips and Techniques sections
enrich the flavor of the book with selected “how to” topics.

Topic Selection and Sequence of Coverage
Once again, as the instructor, the topic selection and sequence of coverage is totally in your
hands! As a simple guideline, Chapters 1-7 were designed to be covered in sequence and
Chapters 8 – 14 were designed to be selectively covered in whatever sequence the instructor
prefers. But, of course, the nature of the Alice environment makes it easy to teach the chapters in
a different order.
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