diff options
| author | elioat <elioat@tilde.institute> | 2023-08-23 07:52:19 -0400 |
|---|---|---|
| committer | elioat <elioat@tilde.institute> | 2023-08-23 07:52:19 -0400 |
| commit | 562a9a52d599d9a05f871404050968a5fd282640 (patch) | |
| tree | 7d3305c1252c043bfe246ccc7deff0056aa6b5ab /js/games/nluqo.github.io/~bh/v1ch0/preface.html | |
| parent | 5d012c6c011a9dedf7d0a098e456206244eb5a0f (diff) | |
| download | tour-562a9a52d599d9a05f871404050968a5fd282640.tar.gz | |
*
Diffstat (limited to 'js/games/nluqo.github.io/~bh/v1ch0/preface.html')
| -rw-r--r-- | js/games/nluqo.github.io/~bh/v1ch0/preface.html | 357 |
1 files changed, 357 insertions, 0 deletions
diff --git a/js/games/nluqo.github.io/~bh/v1ch0/preface.html b/js/games/nluqo.github.io/~bh/v1ch0/preface.html new file mode 100644 index 0000000..012a729 --- /dev/null +++ b/js/games/nluqo.github.io/~bh/v1ch0/preface.html @@ -0,0 +1,357 @@ +<HTML> +<HEAD> +<TITLE>Computer Science Logo Style vol 1:Preface</TITLE> +</HEAD> +<BODY> +<CITE>Computer Science Logo Style</CITE> volume 1: +<CITE>Symbolic Computing</CITE> 2/e Copyright (C) 1997 MIT +<H1>Preface</H1> + +<TABLE width="100%"><TR><TD> +<IMG SRC="../csls1.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/v1ch00.pdf">Download PDF version</A> +<TR><TD align="right"><A HREF="../v1-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-1">MIT +Press web page for Computer Science Logo Style</A> +</TABLE></TABLE> + +<HR> + +<P>This book isn't for everyone. + +<P>Not everyone needs to program computers. There is a popular myth that +if you aren't "computer literate," whatever that means, then you'll +flunk out of college, you'll never get a job, and you'll be poor and +miserable all your life. The myth is promoted by computer +manufacturers, of course, and also by certain educators and writers. + +<P>The truth is that no matter how many people study computer programming +in high school, there will still be only a certain number of +programming jobs. When you read about "jobs in high-tech industry," +they're talking mostly about manufacturing and sales jobs that are no +better paid than any other manufacturing jobs. (Often, these days, +those jobs are exported to someplace like Taiwan where they pay +pennies a day.) It's quite true that many jobs in the future will +involve <EM>using</EM> computers, but the computers will be disguised. +When you use a microwave oven, drive a recently built car, or play a +video game, you're using a computer, but you didn't have to take a +"computer literacy" course to learn how. Even a computer that +looks like a computer, as in a word processing system, can be mastered +in an hour or two. + +<P>This book is for people who are interested in computer programming +because it's fun. + +<P><H2>The Intellectual Content of Computer Programming</H2> + +<P>When I wrote the first edition of this book in 1984, I said that the study +of computer programming was intellectually rewarding for young children in +elementary school, and for computer science majors in college, but that high +school students and adults studying on their own generally had an +intellectually barren diet, full of technical details of some particular +computer brand. + +<P>At about the same time I wrote those words, the College Board was +introducing an Advanced Placement exam in computer science. Since then, the +AP course has become popular, and similar official or semi-official computer +science curricula have been adopted in other countries as well. Meanwhile, +the computers available to ordinary people have become large enough and +powerful enough to run serious programming languages, breaking the monopoly +of BASIC. + +<P>So, the good news is that intellectually serious computer science is within +the reach of just about everyone. The bad news is that the curricula tend +to be imitations of what is taught to beginning undergraduate computer +science majors, and I think that's too rigid a starting point for +independent learners, and especially for teenagers. + +<P>See, the wonderful thing about computer programming is that it <EM>is</EM> +fun, perhaps not for everyone, but for very many people. There aren't many +mathematical activities that appeal so spontaneously. Kids get caught up in +the excitement of programming, in the same way that other kids (or maybe the +same ones) get caught up in acting, in sports, in journalism (provided the +paper isn't run by teachers), or in ham radio. If schools get too serious +about computer science, that spontaneous excitement can be lost. I once +heard a high school teacher say proudly that kids used to hang out in his +computer lab at all hours, but since they introduced the computer science +curriculum, the kids don't want to program so much because they've learned +that programming is just a means to the end of understanding the +curriculum. No! The ideas of computer science are a means to the end of +getting computers to do what you want. + +<P><H2>Computer Science Apprenticeship</H2> + +<P>My goal in this series of books is to make the goals and methods of a +serious computer scientist accessible, at an introductory level, to +people who are interested in computer programming but are not computer +science majors. If you're an adult or teenaged hobbyist, or a teacher +who wants to use the computer as an educational tool, you're +definitely part of this audience. I've taught these ideas to teachers +and to high school students. What I enjoy most is teaching high +school freshmen who bring a love of programming into the class with +them--the ones who are always tugging at my arm to tell me what they +found in the latest <EM>Byte.</EM> + +<P>I said earlier that I think that for most people programming as job training +is nonsense. But if you happen to be interested in +programming, studying it in some depth can be valuable for the same +reasons that other people benefit from acting, music, or being a news +reporter: it's a kind of intellectual apprenticeship. You're learning +the discipline of serious thinking and of taking pride in your work. +In the case of computer programming, in particular, what you're +learning is <EM>mathematical</EM> thinking, or <EM>formal</EM> +thinking. (If you like programming, but you hate mathematics, don't +panic. In that case it's not really mathematics you hate, it's +school. The programming you enjoy is much more like real mathematics +than the stuff you get in most high school math classes.) In these books I +try to encourage this sort of formal thinking by discussing +programming in terms of general rules rather than as a bag of tricks. + +<P>When I wrote the first edition of this book, in 1984, it was controversial +to suggest that not everyone has to learn to program. I was accused of +elitism, of wanting to keep computers as a tool for the rich, while +condemning poorer students to dead-end jobs. Today it's more common that +I have to fight the opposite battle, trying to convince people why <EM> +anyone</EM> should learn about computer programming. After all, there is all +that great software out there; instead of wasting time on programming, +I'm told, kids should learn to use Microsoft Word or Adobe Illustrator +or Macromind Director. At the same time, kids who've grown up with intricate +and beautifully illustrated video games are frustrated by the relatively +primitive results of their own first efforts at programming. A decade ago +it was thrilling to be able to draw a square on a computer screen; today +you can do that with two clicks of a mouse. + +<P>There are two reasons why you might still want to learn to program. One is +that more and more application programs have programming languages built in; +you can customize the program's behavior if you learn to speak its +"extension" language. (One well-known example is the Hypertalk extension +language for the Hypercard program; the one that has everyone excited as I'm +writing this is the inclusion of the Java programming language as the +extension language for the Netscape World Wide Web browser.) But I think a +more important reason is that programming--learning how to express a method +for solving a problem in a formal language--can still be very empowering. +It's not the same kind of fast-paced fun as playing a video game; it feels +more like solving a crossword puzzle. + +<P>I've tried to make these books usable either with a teacher or on your +own. But since the ideas in these books are rather different from those of +most computer science curricula, the odds are that you're reading this on +your own. (When I published the first edition, one exception was that this +first volume was used fairly commonly in teacher training classes, for +elementary school teachers who'd be using Logo in their work.) + +<P><H2>About the Second Edition</H2> + +<P>Three things have happened since the first edition of these books to warrant +a revision. The first is that I know more about computer science than I did +then! In this volume, the topics of recursion and functional programming +are explained better than they were the first time; there is a new chapter on +higher order functions early in the book. There are similar improvements +in the later volumes, too. + +<P>Second, I've learned from both my own and other people's experiences +teaching these ideas. I originally envisioned a style of work in which high +school students would take a programming course in their first year, then +spend several years working on independent projects, and perhaps take a more +advanced computer science class senior year. That's why I put all the +programming language instruction in the first volume and all the project +ideas in the second one. In real life, most students don't spread out their +programming experience in that way, and so the projects in the second volume +didn't get a chance to inspire most readers. In the second edition, I've +mixed projects with language teaching. This first volume teaches the core +Logo capabilities that every programming student should know, along with +sample projects illustrating both the technical details and the range of +possibilities for your own projects. The second volume, <EM>Advanced +Techniques,</EM> teaches more +advanced language features, along with larger and more intricate projects. + +<P>Volume three, <EM>Beyond Programming,</EM> is still a kind of +sampler of a university computer science curriculum. Each chapter is +an introduction to a topic that you might study in more depth during a +semester at college, if you go on to study computer science. Some of +the topics, like artificial intelligence, are about programming +methods for particular applications. Others, like automata theory, +aren't how-to topics at all but provide a mathematical approach to +understanding what programming is all about. I haven't changed the +table of contents, but most of the chapters have been drastically +rewritten to improve both the technical content and the style of +presentation. + +<P>The third reason for a second edition of these books is that the specific +implementations of Logo that I used in 1984 are all obsolete. (One of them, +IBM Logo, is still available if you try very hard, but it's ridiculously +expensive and most IBM sales offices seem to deny that it exists.) The +commercial Logo developers have moved toward products in which Logo is +embedded in some point-and-click graphical application program, with more +emphasis on shapes and colors, and less emphasis on programming itself. +That's probably a good decision for their purposes, but not for mine. +That's why this new edition is based on Berkeley Logo, a free implementation +that I developed along with some of my students. Berkeley Logo is available +for Unix systems, DOS and Windows machines, and Macintosh, and the language is exactly +the same on all platforms. That means I don't have to clutter the text with +footnotes like "If you're using this kind of computer, type that instead." + +<P><H2>Why Logo?</H2> + +<P>Logo has been the victim of its own success in the elementary +schools. It has acquired a reputation as a trivial language for +babies. Why, then, do I use it as the basis for a series of books +about serious computer science? Why not Pascal or C++ instead? + +<P>The truth is that Logo is one of the most powerful programming +language available for home computers. (In 1984 I said "by far the most +powerful," but now home computers have become larger and Logo finally +has some competition.) It is a dialect of Lisp, the +language used in the most advanced research projects in computer +science, and especially in artificial intelligence. Until recently, +all of the <EM>books</EM> about Logo have been pretty trivial, and they +tend to underscore the point by strewing cute pictures of turtles +around. But the cute pictures aren't the whole picture. + +<P>What does it mean for a language to be powerful? It <EM>doesn't</EM> +mean that you can write programs in a particular language that do things you +can't do in some other language. (In that sense, all languages are the +same; if you can write a program in Logo, you can write it in Pascal +or BASIC too, one way or another. And vice versa.) Instead, the power +of a language is a way of measuring how much the language helps you +concentrate on the actual problem you wanted to solve in the first +place, rather than having to worry about the constraints of the language. + +<P>For example, in C, Pascal, Java, and all of the other languages derived +originally from Fortran, the programmer has to be very explicit about +what goes where in the computer's memory. If you want to group 20 +numbers together as a unit, you must "declare an array," saying in +advance that there will be exactly 20 numbers in it. If you change +your mind later and want 21 numbers, too bad. You also have to say +in advance that this array will contain 20 integers, or perhaps 20 +numbers with fractions allowed, or perhaps 20 characters of text--but +not some of each. In Logo the entire process of storage allocation +is <EM>automatic;</EM> if your program produces a list of 20 numbers, +the space for that list is provided with no effort by you. If, later, +you want to add a 21st number, that's automatic also. + +<P>Another example is the <EM>syntax</EM> of a language, the rules for +constructing legal instructions. All the Fortran-derived languages +have a dozen or so types of instructions, each with its own peculiar +syntax. For example, the BASIC <CODE>PRINT</CODE> statement requires a list +of expressions you want printed. If you separate expressions with +commas, it means to print them one way; if you separate them with +semicolons, that means something else. But you aren't allowed to use +semicolons in other kinds of statements that also require lists of +expressions. In Logo there is only one syntax, the one that invokes +a procedure. + +<P>It's not an accident that Logo is more powerful than Pascal or C++; +nor is it just that Logo's designers were smarter. Fortran was +invented before the mathematical basis of computer programming was +well understood, so its design mostly reflects the capabilities (and +the deficiencies) of the computers that happened to be available +then. The Fortran-based languages still have the same fundamental +design, although some of its worst details have been patched over in +the more recent versions like Java and C++. More powerful languages are +based on some particular mathematical model of computing and use that +model in a consistent way. For example, APL is based on the idea of +matrix manipulation; Prolog is based on predicate calculus, +a form of mathematical logic. Logo, like Lisp, +is based on the idea of composition of functions. + +<P>The trouble is that if you're just starting this book, you don't have +the background yet to know what I'm talking about! So for now, please +just take my word for it that I'm not insulting you by asking you to +use a "baby" language. After you finish the book, come back and +read this section again. + +<P>A big change since 1984 is that Logo is no longer the only member of the +Lisp family available for home computers. Another dialect, Scheme, has +become popular in education. Scheme has many virtues in its own right, but +its popularity is also due in part to the fact that it's the language used +in the best computer science book ever written: <EM>Structure and +Interpretation of Computer Programs,</EM> by Harold Abelson and Gerald Jay +Sussman with Julie Sussman (MIT Press/McGraw-Hill, 1985). I have a foot in +both camps, since I am co-author, with Matthew Wright, of <EM>Simply +Scheme: Introducing Computer Science</EM> (MIT Press, 1994), which is sort of +a Scheme version of the philosophy of this book. + +<P>The main difference between Scheme and Logo is that Scheme is more +consistent in its use of functional programming style. For example, in +Scheme, every procedure is what Logo calls an operation--a procedure that +returns a computed value for use by some other procedure. Instead of +writing a program as a sequence of instructions, as in Logo, the Scheme +programmer writes a single expression whose complexity takes the form of +composition of functions. + +<P>The Scheme approach is definitely more powerful and cleaner for writing +advanced projects. Its cost is that the Scheme learner must come to terms +from the beginning with the difficult idea of function as object. Logo is +more of a compromise with the traditional, sequential programming style. +That traditional style is limiting, in the end, but people seem to find it +more natural at first. My guess is that ultimately, Logo programmers who +maintain their interest in computing will want to learn Scheme, but that +there's still a place for Logo as a more informal starting point. + +<P><H2>Hardware and Software Requirements</H2> + +<P>The programs in this series of books are written using Berkeley Logo, a free +interpreter that is available on diskette from the MIT Press or on the +Internet. (Details are in Appendix A.) Berkeley Logo runs on Unix systems, +DOS and Windows machines, and Macintosh. + +<P>Since Berkeley Logo is free, I recommend using it with this book, even if +you have another version of Logo that you use for other purposes. One of +the frustrations I had in writing the first edition was dealing with all the +trivial ways in which different Logo dialects differ. (For example, if you +want to add 2 and 3, can you say <CODE>2+3</CODE>, or do you have to put spaces +around the plus sign? Different dialects answer this question differently.) +Nevertheless, the examples in this first volume should be workable in just +about any Logo dialect with some effort in fixing syntactic differences. +The later volumes in the series, though, depend on advanced features of +Berkeley Logo that are missing from many other dialects. + +<P>The Berkeley Logo distribution includes the larger programs from these +books. When a program is available in a file, the filename is shown at +the beginning of the chapter. (There are only a few of these in the +first volume, but more in later volumes.) + +<P><H2>Words of Wisdom</H2> + +<P>The trick in learning to program, as in any intellectual skill, is to +find a balance between theory and practice. This book provides the +theory. One mistake would be to read through it without ever touching +a computer. The other mistake would be to be so eager to get your +hands on the keyboard that you just type in the examples and skip over +the text. + +<P>There are no formal exercises at the ends of chapters. That's because +(1) I hate a school-like atmosphere; (2) you're supposed +to be interested enough +already to explore on your own; and (3) I think it's better to +encourage your creativity by letting you invent your own exercises. +However, at appropriate points in the text you'll find questions like +"What do you think would happen if you tried thus-and-such?" and +suggestions for programs you can write. These questions and activities are +indicated by this symbol: ». You'll +get more out of the book if you take these questions seriously. + +<P>If you're not part of a formal class, consider working with a friend. +Not only will you keep each other from handwaving too much but it's +more fun. + +<P> + +<P><A HREF="../v1-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> |