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diff --git a/js/games/nluqo.github.io/~bh/v2ch0/preface.html b/js/games/nluqo.github.io/~bh/v2ch0/preface.html new file mode 100644 index 0000000..cec9ca3 --- /dev/null +++ b/js/games/nluqo.github.io/~bh/v2ch0/preface.html @@ -0,0 +1,272 @@ +<HTML> +<HEAD> +<TITLE>Computer Science Logo Style vol 2:Preface</TITLE> +</HEAD> +<BODY> +<CITE>Computer Science Logo Style</CITE> volume 2: +<CITE>Advanced Techniques</CITE> 2/e Copyright (C) 1997 MIT +<H1>Preface</H1> + +<TABLE width="100%"><TR><TD> +<IMG SRC="../csls2.jpg" ALT="cover photo"> +<TD><TABLE> +<TR><TD align="right"><CITE><A HREF="http://www.cs.berkeley.edu/~bh/">Brian +Harvey</A><BR>University of California, Berkeley</CITE> +<TR><TD align="right"><BR> +<TR><TD align="right"><A HREF="../pdf/v2ch00.pdf">Download PDF version</A> +<TR><TD align="right"><A HREF="../v2-toc2.html">Back to Table of Contents</A> +<TR><TD align="right">[no back] +chapter thread <A HREF="ack.html"><STRONG>NEXT</STRONG></A> +<TR><TD align="right"><A HREF="https://mitpress.mit.edu/books/computer-science-logo-style-second-edition-volume-2">MIT +Press web page for <CITE>Computer Science Logo Style</CITE></A> +</TABLE></TABLE> + +<HR> + +<P>This is the second volume of <EM>Computer Science Logo Style,</EM> a +three-volume series that uses the Logo programming language as the medium +for a presentation of a range of topics in computer science. The main +audience I had in mind for these books was high school students, but it's +turned out that they have also been used in teacher training, and to some +extent by independent adult learners. + +<P>In the first edition, the first volume was a complete Logo tutorial, +explaining all of the features of the language; the second volume was +entirely devoted to programming projects. (The third volume, then and +now, is a sampler of topics from undergraduate computer science courses.) +My idea was that students would spend their first year in an intensive +programming course, and would then pursue their own programming projects +on an independent study basis, using my projects as examples. + +<P>As it turned out, people found the first volume both too hard and too easy. +It was too hard because it arrived too soon at the more advanced and +complicated features of Logo; it was too easy because the actual programming +examples were all short enough to fit on a page. Such tiny examples didn't +help the learner extrapolate to the design of a program that could +actually do something interesting. This deficiency may have encouraged +some readers to conclude that Logo is just a toy, and that serious projects +should be done in a "serious" language such as Pascal or C++. + +<P>In this second edition I've rearranged things. The first volume now teaches +only the core features of Logo, the ones every programmer must understand; +it also includes three of the projects that were originally in the second +volume. This volume is now a more advanced programming text; it alternates +tutorial chapters on advanced language features with example projects that +demonstrate those features. + +<P>The project chapters serve two purposes at once. First, each project is an +example of something you might actually want to do. The emphasis +is on getting the computer to do something fun and interesting. Each of the +projects in this book is here because I thought I'd enjoy writing it +myself, not because it fit some subtle pedagogic purpose. The projects are +offered as case studies, as examples to inspire your own creative efforts. + +<P>At the same time, I <EM>am</EM> a teacher, and in this book I'm trying to +teach some ideas about programming technique and programming style. Often +there is an easy way and a hard way to achieve a certain result, and you're +better off if you know the easy way. Nobody has a complete list of such +techniques; you'll be learning new ones for as long as you maintain your +interest in computer programming. The ones I discuss in this book are the +ones that came up in these particular projects. Ideally, as your teacher, I +would look over your shoulder while you're working, and I'd tell you about +the techniques that apply to <EM>your</EM> projects. I can't do that in a +book, and so instead I'm presenting some projects of my own and discussing +them as I would discuss your projects if I knew you personally. + +<P>With one exception, each example chapter comes after a tutorial chapter that +has introduced a new Logo programming technique, and that technique is used +in the project. (The exception, the pattern matching project, is an advanced +programming technique in its own right, and is used in a later project.) +But the technique from the previous chapter is rarely the most important +aspect of the project! Each project exhibits many different techniques, +and the project chapters describe some of them. + +<P>This book does not make much explicit reference to the first volume, but to +understand the discussion here, you should be familiar with the ideas +presented in Volume 1: evaluation, procedures, locality, iteration, +recursion, mapping, predicates, operations, and so on. + +<P>Teaching and learning, by the way, don't necessarily imply a classroom in a +school. I like to imagine you curled up with this book in front of your +home computer, playing around with one of these projects just for the fun of +it. Pretend I'm a friend or relative who happens to be a professional +computer scientist. On the other hand, if you <EM>are</EM> reading this for +a course in a school, you have the advantage of a living teacher who can +provide the kind of individual attention to your specific projects that I +can't. There are advantages and disadvantages either way. + +<P><H2>About the Projects</H2> + +<P>Although I now have the projects linked with tutorial chapters, in the +first edition I organized them into five categories, based not on the +programming techniques used but rather on the purposes of the programs. The +projects reflect aspects of my own character: I came to computers by way of +an early interest in mathematics; my computing background is in +artificial intelligence and in systems programming; I tend +to think in words, not in pictures. I think it may give the collection of +projects a more coherent feel if I explain the categories in which they +were written, even though the book is no longer organized around +those categories. + +<P>The first is cryptography. One of the first books I can +remember buying, as a child in elementary school, was about secret codes. +Besides the universal appeal of knowing a secret, cryptography was +interesting to me because it's a <EM>mathematical</EM> sort of puzzle, like +those logic problems about who lives in the yellow house. The +Cryptographer's Helper project in this volume includes a very small effort +at artificial intelligence: the program makes some guesses, on its own, to +start solving a cryptogram. The Playfair Cipher project, now moved to the +first volume, deals with a more complicated technique for encoding a +message, but it doesn't try to break such a code. + +<P>The second category is games. I'm not a video game enthusiast; hand-eye +coordination isn't my strong point. (I never really learned to ride a +bicycle!) Anyway, writing video game programs depends too much on the +particular hardware of your computer, so I can't do it in this general +book.<SUP>*</SUP> Instead I've written two simple +strategy games. In the first volume is a program that plays tic-tac-toe. This game +is extremely trivial for a human being, but it's surprisingly hard to +formulate strategy rules that are simple and precise enough to embody in a +computer program. Also, it's an opportunity to throw in a little bit of +graphics programming, to draw the board and fill it with Xs and Os. In this +volume is a program that deals out a hand of solitaire and maintains the display of +the layout as you play the hand. Before I wrote this program, I had been +feeling bored and lonely for an extended period, and I was wasting a lot of +time playing solitaire myself. I figured it would be more productive to +write a computer program! + +<P><SMALL><BLOCKQUOTE><SMALL><SUP>*</SUP>You can find a video game that I wrote in the collection +<EM>LogoWorks: Challenging Programs in Logo</EM>, edited by Solomon, +Minsky, and Harvey (McGraw-Hill, 1985).</SMALL></BLOCKQUOTE></SMALL><P>The third category is mathematics. I once spent some time working as a +systems programmer at a computer music research center in Paris, and this +volume includes a project about Fourier analysis, the mathematical +basis of computer music. The project demonstrates graphically how a complex +waveform, representing the texture of a sound, can be built up from much +simpler elements. In the first volume is a program to solve the kind of +problem, often found on IQ tests, in which you are given pitchers of certain +sizes and asked to use them to measure a given amount of water by pouring +back and forth. This project illustrates the idea of searching through a +"solution space" of possible pouring steps. + +<P>The fourth category is that of utility programs. This is actually +the area of programming I know best: writing things that are not complete +applications in themselves, but rather tools to help in the creation of even +larger projects. For the second edition I've replaced the original +projects in this category with two new ones. The project Finding File +Differences is a utility program that can be used to compare two versions +of a file to see what's changed from the old one to the new one. Then +there is a compiler for the BASIC programming language; besides illustrating +the idea of program as data--the compiler generates new Logo procedures +to carry out the instructions in a BASIC program--this project may help to +prepare the reader for the more complicated Pascal compiler in the third +volume. + +<P>The fifth category is pattern matching. This category +combines my interests in systems programming and +artificial intelligence. The first project is a tool, like the +ones in the utilities category, but it's a tool designed specifically for +artificial intelligence applications: a pattern matcher. This program +compares a particular list with a general template, or pattern. Instead of +checking for exact equality like <CODE>equalp</CODE>, the pattern matcher checks +for a kind of "fill in the blanks" partial equality. The second project +in this category uses the pattern matcher to implement <CODE>doctor</CODE>, another famous +artificial intelligence program that simulates a conversation with the user. + +<P><H2>About This Series</H2> + +<P><EM>Computer Science Logo Style</EM> is intended to bring to the hobbyist +audience a particular point of view about computer science: the +artificial intelligence view. This way of looking at computers is +quite different from the more usual software engineering approach. +In that approach, you are always dealing with a +very well-defined problem, and are looking for the best way to solve it. +Software engineers like to start with a formal problem statement, and then +design a computer program to fit. They believe that the design process +should be <EM>top-down</EM>; you should start with the overall structure and +work down to the details. Their preferred programming language is +Pascal. + +<P>In artificial intelligence, the problems are not usually so well +defined. Starting with a vague problem statement like "develop a good +strategy for playing chess," AI programmers can't begin with a rigid program +specification. Instead, they build <EM>tools:</EM> program fragments that +can be pieced together to form larger programs. The programming process +involves writing code, testing, coming up with new ideas, and modifying the +program interactively. This process is encouraged by an interactive +language like Lisp or Logo. + +<P>Computer programming is a great intellectual hobby; it provides the same +opportunity for creative, concrete work in mathematical thinking that +drama or creative writing does for verbal thinking. A learner can have +years of intellectual adventure just learning to write better and better +programs. Finally, though, there may come a time +when the learner gets bored with just writing more and more programs, and +seeks a deeper understanding of the issues behind this practical work. The +third volume of this series, <EM>Beyond Programming,</EM> addresses +the needs of these learners by introducing them to some of the elements of +university-level computer science, still in the context of Logo programming. + +<P><H2>How to Read This Book</H2> + +<P>You should have each program actually available to you on a computer as you +read about it. These programs can be downloaded +<A HREF="../downloads/csls-programs">here</A>. + +<P>There are many dialects of Logo; this book uses Berkeley Logo, a free +version available for PC, Macintosh, and Unix systems. The more fundamental +Logo techniques used in the first volume are more or less standard among +Logo implementations, but some of the advanced techniques in this volume +are unique to Berkeley Logo. Download Berkeley Logo +<A HREF="../logo.html">here</A>. + +<P>The programs you see here are essentially the programs I wrote as I was +trying to get each project to work. I didn't start with a particular +programming style in mind and then invent an example to illustrate the +style. It's not always obvious what is the "correct" style for a given +problem; sometimes one way is much easier to understand, for example, while +a different solution may run much more efficiently. The comments in +each chapter sometimes suggest alternative ways in which I might have +written some piece of the program. I try to explain why I chose the style I +did, although sometimes the real explanation is simply that that's the first +thing I thought of. I've modified almost all of these programs for the +second edition, and some of the chapters explain my second thoughts. + +<P>Each example chapter begins with an explanation of what the project is all about. +Remember that these projects were meant to be interesting in themselves, not +just as vehicles for a discussion of programming techniques! The discussion +in each chapter ends with a return to the purpose of the project, with +suggestions for how that purpose might be extended. One source of ideas for +projects of your own is to extend someone else's work, and one important +purpose of this book is to give you ideas for such starting points. +In between comes a technical discussion of the programming techniques used. + +<P>What I do <EM>not</EM> provide, generally, is a guided tour of every +procedure. One of the things you should learn from this book is the ability +to read a long program on your own. You should recognize some of the +typical categories of procedures, like ones that apply a given command to +each member of a list. In the discussions, rather than explain every +detail, I try to focus your attention on the parts of the program that seem +to illuminate some more general technical issue. A complete listing of the +program is at the end of each example chapter. + +<P>The programs in this book are copyright, but you can use, copy, and +redistribute them freely; the exact terms are given in the GNU General +Public License, which is distributed with the programs and is printed +in the first volume of this series. Essentially, the only restriction +is that you can't use these programs as the basis for your own commercial +programs; if you extend these projects, you can only distribute your +extensions on the same free terms. Share ideas, don't hoard them! + +<P> + +<P><A HREF="../v2-toc2.html">(back to Table of Contents)</A> +<P>[no back] +chapter thread <A HREF="ack.html"><STRONG>NEXT</STRONG></A> + +<P> +<ADDRESS> +<A HREF="../index.html">Brian Harvey</A>, +<CODE>bh@cs.berkeley.edu</CODE> +</ADDRESS> +</BODY> +</HTML> |