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| author | elioat <elioat@tilde.institute> | 2023-08-23 07:52:19 -0400 |
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diff --git a/js/games/nluqo.github.io/~bh/v1ch1/explor.html b/js/games/nluqo.github.io/~bh/v1ch1/explor.html new file mode 100644 index 0000000..8b5682b --- /dev/null +++ b/js/games/nluqo.github.io/~bh/v1ch1/explor.html @@ -0,0 +1,449 @@ +<HTML> +<HEAD> +<TITLE>Computer Science Logo Style vol 1 ch 1: Exploration</TITLE> +</HEAD> +<BODY> +<CITE>Computer Science Logo Style</CITE> volume 1: +<CITE>Symbolic Computing</CITE> 2/e Copyright (C) 1997 MIT +<H1>Exploration</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/v1ch01.pdf">Download PDF version</A> +<TR><TD align="right"><A HREF="../v1-toc2.html">Back to Table of Contents</A> +<TR><TD align="right"><A HREF="../v1ch0/ack.html"><STRONG>BACK</STRONG></A> +chapter thread <A HREF="https://people.eecs.berkeley.edu/~bh/v1ch2/v1ch2.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>The name Logo comes from the Greek word <EM>logos,</EM> which means +"word." In contrast to earlier programming languages, which +emphasized arithmetic computation, Logo was designed to manipulate +language--words and sentences. + +<P>Like any programming language, Logo is a general-purpose tool that +can be approached in many ways. Logo programming can be understood +at different levels of sophistication. It has been taught to +four-year-olds and to college students. Most of the books about +Logo so far have been introductory books for young beginners, but <EM> +this</EM> book is different. It's for somewhat older learners, +probably with some prior computer experience, although not +necessarily Logo experience. + +<P>This book was written using the Berkeley Logo dialect, a version +of Logo that's available at no cost for PCs, Macintoshes, and Unix +systems. Recent commercial Logo +dialects have emphasized the control of real-time animation, +robotics, and other such application areas, somewhat at the +expense of more traditional Logo features designed to be useful +in the development of larger and more complex programs. Berkeley +Logo follows the traditional design, so you may miss some +"bells and whistles" that you associate with Logo from +elementary school. In fact, we'll hardly do any graphics +in this book! + +<P>Some of the details you'll have to know in order to work with Logo +depend on the particular kind of computer you're using. This +book assumes you already know some things about your computer: + +<UL> +<LI> How to turn on your computer and start Logo +<LI> How to type a command, ending with the RETURN key +<LI> How to use control keys to correct typing mistakes +<LI> How to use a text editing program +</UL> + +<P> +These points I've listed aren't actually part of the Logo +<EM>language</EM> itself, but they're part of the Logo programming +<EM>environment.</EM> Appendix A has a brief guide to some of these +machine-specific aspects, but if you've never used a computer before +at all, start by working with some application programs +to get the feel of the machine. + +<P>On the other hand, I'd like to pretend that you know nothing about +the Logo language--the primitive procedures, the process of +procedure definition, and so on--even if you've really used Logo +in elementary school. The reason for this pretense is +that I want you to think about programming in what will probably be +a new way. The <EM>programs</EM> may not be new to you, but the <EM> +vocabulary</EM> with which you think about them will be. I'm warning +you about this ahead of time because I don't want you to skip over +the early chapters, thinking that you already know what's in them. + +<P>Okay, it's time to start Logo running on your computer. You should +then see a screen that says something like + +<P><PRE>Welcome to Berkeley Logo version 3.3 +? +</PRE> + +<P>The question mark is Logo's <EM>prompt.</EM> When you +see the question mark, it means that the computer is prepared for you +to type in a Logo <EM>instruction</EM> and that Logo will carry +out the instruction as soon as you finish it. + +<P> +<H2>Getting Acquainted with Logo...</H2> + +<P>Right now, type this instruction: + +<P><PRE>repeat 50 [setcursor list random 75 random 20 type "Hi] +</PRE> + +<P>Remember that square brackets <CODE>[]</CODE> are different from +parentheses <CODE>()</CODE>. Also remember that it's important to put +spaces between words. However, it doesn't matter whether you use +<CODE>UPPER CASE</CODE> or <CODE>lower case</CODE> letters in the words that Logo understands. + +<P>If all goes well, Logo will cheerfully greet you by scattering <CODE> +Hi</CODE>s all over the screen. If all doesn't go well, you probably +misspelled something. Take a look at what you typed, and try again. + +<P>Afterward, you can clear the screen by typing <CODE>cleartext</CODE> or +its abbreviation <CODE>ct</CODE>. + +<P> +<H2>... in Two Senses</H2> + +<P>I thought it would be appropriate to start exploring Logo by having +it say hello. You and Logo can get acquainted as you would with +another person. + +<P>But, of course, the point of the exercise is to get acquainted with +Logo in a more serious sense too. You're seeing what a Logo +instruction looks like and a little bit about what kinds of things +Logo can do. In this first chapter the kind of acquaintance I have +in mind is relatively superficial. I'm trying to get across a broad +sense of Logo's flavor rather than a lot of details. So I'm not +explaining completely what we're doing here. For that reason, the +second chapter will repeat some of the same activities, but I'll +give a more detailed discussion there. + +<P>Perhaps you've made Logo's acquaintance before, probably through the +medium of turtle graphics. In that first introduction you may have +explored Logo's ability to manipulate text as well as graphics. But +maybe not. Writing a book like this, it's not easy for me to carry +on a conversation with someone I haven't met, so in this +introduction I may be saying too much or too little for your +individual situation. I hope that by the second chapter you and the +other readers will all be ready for the same discussion. + +<P>If you haven't used Logo before, or if you've used only the part of +Logo that has to do with turtles, look at the instruction I asked +you to type earlier. Think about the different parts of that +instruction, the words like <CODE>repeat</CODE> and <CODE>random</CODE> and <CODE> +setcursor</CODE>. Try to figure out what each one means. Then see +if you can figure out an experiment to decide if you've understood +each word correctly! Later, we'll go over all these details and +you'll learn the "official" explanations. But the kind of +experimenting I'm suggesting isn't pointless. This kind of +exploration may raise questions in your mind, not just about the +meanings of the Logo words but about how they're connected together +in an instruction, or about <EM>why</EM> a word means just what it +does rather than something a little different. + +<P><H2>Another Greeting</H2> + +<P>Here is a somewhat less "scatterbrained" greeting instruction: + +<P><PRE>repeat 20 [repeat random 30 [type "Hi] print []] +</PRE> + +<P>Try that one. Compare it to the one we started with. +Which do you like better? Do you prefer random scattering, or +orderly rows? Perhaps this question will teach you something about +your own personality! + +<P><H2>Fooling Around</H2> + +<P>Then again, maybe you think this is all silly. If so, I'd like to +try to convince you that there are some good, serious reasons for +you to take a lighthearted approach to computer programming, no +matter how serious your ultimate goals may be. + +<P>There are two aspects to learning how to program in a language like +Logo. One aspect is memorizing the vocabulary, just as in learning +to speak French. If you flip through the reference manual that came +with your Logo,<SUP>*</SUP> you'll find that it's a sort of dictionary, +translating each Logo word into a bunch of English words that +explain it. But the second aspect is to learn the "feel" of +Logo. What kinds of problems does Logo handle particularly well? +What are the examples of programming <EM>style</EM> that correspond +to the idioms of a human language? What do you do when something +doesn't work? + +<P><SMALL><BLOCKQUOTE><SMALL><SUP>*</SUP>If you're using Berkeley Logo, it's in a file +named <CODE>usermanual</CODE> (or <CODE>userman.ual</CODE> if you're +using a DOS machine) that should be installed along with the Logo +program. The Berkeley Logo reference manual is also an appendix +to Volume 2 of this series.</SMALL></BLOCKQUOTE></SMALL><P>It is by fooling around with Logo that you learn this second aspect +of the language. Starting with the second chapter of this book, +we'll be going through plenty of dry, carefully analyzed fine points +of Logo usage. But as we progress, you should still be fooling +around, on the computer, with the ideas in the chapters. + +<P>In fact, I think that that kind of intellectual play is the best +reason for learning about computer programming in the first place. +This is true whether you are a kid programming for the fun of it or +an adult looking for a career change. The most successful computer +programmers aren't the ones who approach programming as a task they +have to carry out in order to get their paychecks. They're the ones +for whom programming is a joyful game. Just as a baseball diamond +is a good medium in which you can exercise your body, the computer +is a good medium in which you can exercise your mind. That's the +real virtue of the computer in education, not anything about job +training or about arithmetic drill. + +<P><H2>A Slightly Longer Conversation</H2> + +<P>The Logo words such as <CODE>print</CODE> and <CODE>random</CODE> are the names of +<EM>procedures,</EM> little pieces of computer program that are +"specialists" in some particular task. We are now going to add to +Logo's repertoire by inventing a new procedure named <CODE>hi</CODE>. +At the question mark prompt, start by typing this: + +<P><PRE>to hi +</PRE> + +<P>The word <CODE>to</CODE> here is short for "here's how to." The +name is intended to suggest the <EM>metaphor</EM> that what +you're doing when you write computer programs is to <EM>teach</EM> +the computer a new skill. Metaphors like this can be very helpful +to you in understanding a new idea. (Just ask any English +teacher.) I'll point out other metaphors from time to time. + +<P>Logo should have responded to this instruction by printing a +different prompt character. Instead of the question mark, +you should now see a greater-than sign (<CODE>></CODE>) at the beginning +of the line: + +<P><PRE>? <U>to hi</U> +> +</PRE> + +<P>(Whenever I show an interaction with the computer in this +book, I'll show the part that you're supposed to type <CODE> +<U>underlined</U></CODE>; what the computer prints in response is <CODE>not +underlined</CODE>. +But I won't underline when I'm only showing what you type and +not a complete interaction.) This new prompt means that Logo will +not immediately carry out whatever instructions you type; instead +Logo will remember these instructions as part of the new procedure +<CODE>hi</CODE>. Continue typing these lines: + +<P><PRE>print [Hi. What's your name?] +print sentence [How are you,] word first readlist "? +ignore readlist +print [That's nice.] +end +</PRE> + +<P>Again, be careful about the spaces and punctuation. After +the last line, the one that just says <CODE>end</CODE>, Logo should go back +to the question mark prompt. Now just type + +<P><PRE>hi +</PRE> + +<P>on a line by itself. You can carry on a short +conversation with this program. Here's what happened when I tried +it. + +<P><PRE>? <U>hi</U> +Hi. What's your name? +<U>Brian Harvey</U> +How are you, Brian? +<U>I'm fine.</U> +That's nice. +</PRE> + +<P>If something unexpected happens when you try it, perhaps +you made a typing mistake. If you know how, you can fix such +mistakes using the Logo editor. If not, you'll have a chance to +review that process later, but for now, just start over again but +give the procedure a different name. For example, you can say + +<P><PRE>to hi2 +</PRE> + +<P>for the second version of <CODE>hi</CODE>. + +<P>»This program pretends to be pretty smart. It carries on a +conversation with you in English. But of course it isn't really +smart. If you say "I feel terrible" instead of "I'm fine," the +procedure cheerfully replies "That's nice" anyway. How else can +you mess up the program? What programming tools would you need to +be able to overcome the "bugs" in this program? + +<P>(When a paragraph starts with this symbol » it means that +the paragraph asks you to invent something. Often it will be a Logo +program, but sometimes, as in this case, just answers to questions. This is +a good opportunity to take a break from reading, and check on your +understanding of what you've read.) + +<P><H2>A Sneaky Greeting</H2> + +<P>This chapter started as a sort of pun in my mind--the one about +getting acquainted. How should I have Logo introduce itself? I'm +still playing with that idea. Here's another version. + +<P><PRE>to start +cleartext +print [Welcome to Berkeley Logo version 3.3] +type "|? | +process readlist +type "|? | +wait 100 +print [Ha, ha, fooled you!!] +end + +to process :instruction +test emptyp :instruction +iftrue [type "|? | process readlist stop] +iffalse [print sentence [|I don't know how to|] first :instruction] +end +</PRE> + +<P>The vertical bars are used to tell Logo that you want to +include space characters within a word. (Ordinarily Logo pays no +attention to extra spaces between words.) This is the sort of +grubby detail you may not want to bother with right now, but if you +are a practical joker you may find it worth the effort. + +<P><H2>A Quiz Program</H2> + +<P>Before we get on to the next chapter, I'll just show you one more +little program. Try typing this in. As before, you'll see +greater-than prompts instead of question marks while you're doing +it. + +<P> +<PRE>to music.quiz +print [Who is the greatest musician of all time?] +if equalp readlist [John Lennon] [print [That's right!] stop] +print [No, silly, it's John Lennon.] +end +</PRE> + +<P>You can try out this procedure by typing its name as an +instruction.<SUP>*</SUP> + +<P><SMALL><BLOCKQUOTE><SMALL><SUP>*</SUP>It has been suggested by some reviewers of the +manuscript that there may be younger readers who don't know who John Lennon +is. Well, he's the father of Julian Lennon, an obscure rock star of the +'80s, and he used to be in a rock group called the Quarrymen. If you have +trouble with some of the cultural references later in the book you'll have +to research them yourself.</SMALL></BLOCKQUOTE></SMALL><P>»If you don't like my question, you could make up your own procedures +that ask different questions. Let's say you make up one called <CODE> +sports.quiz</CODE> and another called <CODE>history.quiz</CODE>, each asking and +answering one question. You could then put them all together into one +big quiz like this: + +<P><PRE>to total.quiz +music.quiz +sports.quiz +history.quiz +end +</PRE> + +<P><H2>Saving Your Work</H2> + +<P>If you do write a collection of quiz procedures, you'll want to save +them so that they'll still be available the next time you use Logo. +Certainly you'll want to save the work you do in later chapters. +You can ask Logo to record all of the definitions you've made as +a <EM>workspace</EM> file using the <CODE>save</CODE> command. For example, +if you enter the instruction + +<P><PRE>save "mystuff +</PRE> + +<P>you are asking Logo to write a disk file called <CODE>mystuff</CODE> +containing everything you've defined. (The next time you use Logo, you can +get back your definitions with the <CODE>load</CODE> command.) + +<P>Don't get confused about the difference between a <EM>procedure</EM> name +and a <EM>workspace</EM> name. Logo beginners sometimes think that <CODE> +save</CODE> saves only a single procedure, the one whose name you tell it (in this +example, a procedure named <CODE>mystuff</CODE>). But the workspace file named +<CODE>mystuff</CODE> will actually contain <EM>all</EM> the procedures you've defined. +In fact, you probably don't have a procedure named <CODE>mystuff</CODE>. + +<P>The format for the name of a disk file will depend on the kind of computer +you're using, whether you're writing to a hard disk or a floppy disk, and so +on. Just use whatever file name format your system requires in other +programs, preceded by the quotation mark that tells Logo you're providing +a word as the input to the <CODE>save</CODE> command. + +<P><H2>About Chapter 2</H2> + +<P>In this chapter the emphasis has been on <EM>doing</EM> things. You've +been playing around with some fairly intricate Logo instructions, +and if you don't understand everything about the examples, don't +let that worry you. + +<P>Chapter 2 has the opposite emphasis. There is very little to do, +and the examples will seem quite simple, perhaps even insultingly +simple! But the focus of the chapter is on <EM>understanding</EM> those +simple examples in great detail. + +<P>Logo deserves its reputation as an easy-to-learn language, but it +is also a very sophisticated one. The ease with which Logo can be +learned has lured many people into sloppy thinking habits that make +it hard for them to grow beyond the most trivial programming. By +studying examples that seem easy on the surface, we can start exploring +<EM>below</EM> the surface. The important questions will not be ones +like "what does <CODE>print</CODE> do," but instead ones like "what is going +on <EM>inside</EM> the Logo interpreter when I type <CODE>print</CODE>?" + +<P>Later chapters will strike more of a balance between things to do +and things to think about. If the pace seems slow in chapter 2, glance +back at the table of contents to reassure yourself about how much +territory we'll cover before the end of the book. Then keep in mind +that you'll need the ideas from chapter 2 in order to understand what +comes later. + +<P><H2>No Exercises</H2> + +<P>This is the point in the chapter where you might be expecting a set +of exercises: Problem 1.1, get the computer to print your name. + +<P>There aren't any exercises--but not because you shouldn't try using +Logo at this point. The reason is that part of the challenge is for +<EM>you</EM> to invent things to try, not just rely on me for your ideas. +In each chapter there will be some sample procedures to illustrate +the new information in the chapter. You should try to invent programs +that use those ideas. + +<P>But I hope it's clear by now that I don't want you to do this with +a sense of duty. You should play with the ideas in each chapter only +to the extent that it's interesting and mind-stretching for you to +do so. + +<P>In this chapter I really haven't yet told you any of the rules for +putting together Logo instructions. (I'll do that in Chapter 2.) +So you shouldn't get discouraged or feel stupid if you don't get very +far, right now, in playing with Logo. It will be a few more chapters +before you should expect to feel really <EM>confident</EM> about undertaking +new projects of your own. But you won't break anything by trying +now. Go ahead, fool around! + +<P><A HREF="../v1-toc2.html">(back to Table of Contents)</A> +<P><A HREF="../v1ch0/ack.html"><STRONG>BACK</STRONG></A> +chapter thread <A HREF="https://people.eecs.berkeley.edu/~bh/v1ch2/v1ch2.html"><STRONG>NEXT</STRONG></A> + +<P> +<ADDRESS> +<A HREF="../index.html">Brian Harvey</A>, +<CODE>bh@cs.berkeley.edu</CODE> +</ADDRESS> +</BODY> +</HTML> |