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diff --git a/js/games/nluqo.github.io/~bh/ssch27/appendix-running.html b/js/games/nluqo.github.io/~bh/ssch27/appendix-running.html new file mode 100644 index 0000000..a52f9e8 --- /dev/null +++ b/js/games/nluqo.github.io/~bh/ssch27/appendix-running.html @@ -0,0 +1,426 @@ +<HTML> +<HEAD> +<TITLE>Simply Scheme Appendix A: Running Scheme</TITLE> +</HEAD> +<BODY> +<CITE>Simply Scheme</CITE>: +<CITE>Introducing Computer Science</CITE> 2/e Copyright (C) 1999 MIT +<H2>Appendix A</H2> +<H1>Running Scheme</H1> + +<TABLE width="100%"><TR><TD> +<IMG SRC="../simply.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"><CITE><A HREF="http://ccrma.stanford.edu/~matt">Matthew +Wright</A><BR>University of California, Santa Barbara</CITE> +<TR><TD align="right"><BR> +<TR><TD align="right"><A HREF="../pdf/ssch27.pdf">Download PDF version</A> +<TR><TD align="right"><A HREF="../ss-toc2.html">Back to Table of Contents</A> +<TR><TD align="right"><A HREF="../ssch26/preview.html"><STRONG>BACK</STRONG></A> +chapter thread <A HREF="appendix-cl.html"><STRONG>NEXT</STRONG></A> +<TR><TD align="right"><A HREF="http://mitpress.mit.edu/0262082810">MIT +Press web page for <CITE>Simply Scheme</CITE></A> +</TABLE></TABLE> + +<HR> + +<P>The precise incantations needed to start Scheme depend on the particular +version you're using and the model of computer and operating system you have. +It's beyond the scope of this book to teach you the first steps in using a +computer; we assume you've already used other programs, if not Scheme. +But in this appendix we suggest a few general ideas and point out some +knotty details. + +<P>One thing that beginners often forget is that a computer generally has many +different programs available, and each one has its own capabilities and its +own method of operation. If you think of yourself as interacting with "the +computer," you're likely to try to use a command suitable for one program +when you're actually using a different program. In learning to program in +Scheme, you'll probably use at least three programs: Scheme itself, the +operating system's <EM>shell</EM> (which is callled <EM>finder</EM> on the +Macintosh and <EM>explorer</EM> on Windows), and a text editor. (The text +editor may be part of the Scheme package or it may be an entirely separate +program.) The shell allows you to run other programs, such as a printing +utility or an electronic mail reader. + +<P>If you say <CODE>(+ 2 3)</CODE> to your text editor, it won't respond by printing +<CODE>5</CODE>. Instead, it will insert the seven characters that you typed into +the file that you're editing. If you type the same thing to Scheme, it will +evaluate the expression. + +<P><H2>The Program Development Cycle</H2> + +<P>Scheme is an interactive language: You can write a program by typing +its definition directly into the Scheme interpreter. This ability +to interact with Scheme is a great advantage for one-time +calculations and for exploratory work, but it's not the best +approach for the systematic development of a large program. + +<P>There are two issues to consider. First, when writing a large program, you +generally don't get it perfect the first time. You make both typing errors +and program logic errors, and so you must be able to revise a definition. +Typing directly to Scheme, the only way to make such a revision is to retype +the entire definition. Second, Scheme does not provide a mechanism to save +your work in a permanent file. + +<P>For these reasons, programs are generally typed into another program, a text +editor, rather than directly at the Scheme prompt. As we'll explain in the +next section, there are several ways in which an editing program can be <EM>integrated</EM> with Scheme, so that the work you do in the editor can be +communicated easily to Scheme. But the distinction between Scheme and the +editor is easiest to understand if we start by considering the worst possible +situation, in which the two are not integrated. + +<P>Imagine, therefore, that you have two separate programs available on +your computer. One program is a Scheme interpreter. When you start +Scheme, you may see some initial message, and then you see a prompt, +which is a signal from Scheme that it's ready for you to type +something. In this book we've used the character "<CODE>></CODE>" as the +prompt. Then, as we explain in the text, you can type an +expression, and Scheme will compute and print the value: + +<P><PRE>> (+ 2 3) +5 +</PRE> + +<P>Your other program is a text editor. This might be a +general-purpose word processing program, with facilities for +fancy text formatting, or it might be an editor intended +specifically for computer programs. Many editors "know" about +Lisp programs and have helpful features, such as automatic +indentation, selection of complete expressions, and showing you the +matching open parenthesis when you type a close parenthesis. + +<P>To write a program, you use the editor. Although you are typing +Scheme expressions, you're not talking to Scheme itself, and so the +expressions are not evaluated as you type them. Instead, they just +appear on the screen like any other text. When you're ready to try +out your program, you tell the editor to save the text in a file. +(The command to save the program text is the same as it would be for +any other text; we assume that you already know how to use the +editor on your computer.) You can give the file any name you want, +although many people like to use names like <CODE><EM>something</EM></CODE><CODE>.scm</CODE> to make it easy to recognize files that contain Scheme +programs. + +<P>Now you switch from the editor to Scheme. To read your program file into +Scheme, you enter the expression + +<P><PRE>(load "<EM>something</EM>.scm") +</PRE> + +<P>This tells Scheme to read expressions from the specified +file.<A NAME="text1" HREF="appendix-running.html#ft1">[1]</A> + +<P>Once Scheme has read the program definitions from your file, you +can continue typing expressions to Scheme in order to test your +program. If this testing uncovers an error, you will want to +change some definition. Instead of typing the changed definition +directly into Scheme, which would only make a temporary change in +your program, you switch back to the editor and make the change in +your program file. Then switch back to Scheme, and <CODE>load</CODE> the +corrected file. + +<P>This sequence of steps—edit a file, make changes, save the +file, switch to Scheme, load the file, test the program, find an +error—is called a "development cycle" because what comes +after "find an error" is editing the file, beginning another +round of the same steps. + +<P><H2>Integrated Editing</H2> + +<P>The development process can become much more convenient if Scheme and the +editor "know about" each other. For example, instead of having to reload +an entire file when you change one procedure definition, it's faster if your +editor can tell Scheme just the one new definition. There are three general +approaches to this integration: First, the editor can be in overall charge, +with the Scheme interpreter running under control of the editor. Second, +Scheme can be in charge, with the editor running under Scheme's +supervision. Third, Scheme and the editor can be separate programs, both +running under control of a third program, such as a window system, that +allows information to be transferred between them. + +<P>If you're using a Unix system, you will be able to take a +separate editor program and run Scheme from within that editor. +The editor can copy any part of your program into the running +Scheme, as if you had typed it to Scheme yourself. We use Jove, +a free, small, fast version of EMACS. Most people use the more +featureful GNU version of EMACS, which is installed on most Unix +systems and available at <CODE>ftp://prep.ai.mit.edu/pub/gnu/</CODE> and +many mirror sites for download. + +<P>If you're using a Macintosh or Windows version of Scheme, it will probably +come with its own text editor and instructions on how to use it. These +editors typically provide standard word-processing features such as cut and +paste, search and replace, and saving files. Also, they typically have a +way to ask Scheme to evaluate an expression directly from the editor. + +<P>If you're using SCM under DOS, you should read the section "Editing +Scheme Code" in the <CODE>README</CODE> file that comes with the SCM +distribution. It will explain that editing can be done in different +ways depending on the precise software available to you. You can +buy a DOS editor that works like the Unix editors, or you can ask +SCM to start a separate editor program while SCM remains active. + +<P>Finally, if you're running Scheme under Windows or another windowing +operating system (like X or the Macintosh Finder), you can run any editor in +another window and use the cut and paste facility to transfer information +between the editor and Scheme. + +<P><H2>Getting Our Programs</H2> + +<P>This book uses some programs that we wrote in Scheme. You'll want these +files available to you while reading the book: + +<P><TABLE> +<TR><TD><CODE>simply.scm</CODE> +<TD>extended Scheme primitives +<TR><TD><CODE>functions.scm</CODE> +<TD>the <CODE>functions</CODE> program of Chapters 2 and 21 +<TR><TD><CODE>ttt.scm</CODE> +<TD>the tic-tac-toe example from Chapter 10 +<TR><TD><CODE>match.scm</CODE> +<TD>the pattern matcher example from Chapter 16 +<TR><TD><CODE>spread.scm</CODE> +<TD>the spreadsheet program example from Chapter 24 +<TR><TD><CODE>database.scm</CODE> +<TD>the beginning of the database project +<TR><TD><CODE>copyleft</CODE> +<TD>the GNU General Public License (see Appendix D) +</TABLE><P> + +In particular, the file <CODE>simply.scm</CODE> must be loaded into Scheme to allow +anything in the book to work. Some Scheme systems allow you to load such a +"startup" file permanently, so that it'll be there automatically from then +on. In other versions of Scheme, you must say + +<P><PRE>(load "simply.scm") +</PRE> + +<P>at the beginning of every Scheme session. + +<P>There are three ways to get these program files: + +<P><P><TABLE><TR><TH align="right" valign="top">•<TD> <TD valign="top">If you have access to the Internet, +the most recent versions of all these files can be found at +<CODE>ftp://anarres.cs.berkeley.edu/pub/scheme/</CODE> + +</TABLE> +<P><TABLE><TR><TH align="right" valign="top">•<TD> <TD valign="top">If you know someone who already has these files, you may copy them +and distribute them freely. (The programs are copyrighted but are provided +under a license that allows unlimited redistribution on a nonprofit +basis; see Appendix D.) +</TABLE><TABLE><TR><TH align="right" valign="top">•<TD> <TD valign="top">If you're stranded on a desert island with nothing but a computer and a +copy of this book, you can type them in yourself; complete listings for all +six programs, plus the GNU Public License, appear in the text of the book. + +</TABLE><P> + +<P><H2>Tuning Our Programs for Your System</H2> + +<P>Almost all of the programs we distribute with this book will work +without modification in the popular versions of Scheme. We've +included "defensive" procedures that allow our programs to work +even in versions that don't conform to current Scheme standards +in various ways. However, there are a few details that we +couldn't make uniform in all versions. + +<P>1. Many versions of Scheme include a <CODE>random</CODE> procedure to generate +random numbers, but the standard does not require it, and so we've provided +one just in case. If your Scheme includes a primitive <CODE>random</CODE>, it's +probably better than the one we provide, because we have no way to choose +a different starting value in each Scheme session. + +<P>Before loading <CODE>simply.scm</CODE> into Scheme, do the following experiment: + +<P><PRE>> (random 5) +</PRE> + +<P>If you get an error message, do nothing. If you get a random +number as the result, edit <CODE>simply.scm</CODE> and remove the definition of +<CODE>random</CODE>. + +<P>2. Do the following experiment: + +<P><PRE>> (error "Your error is" "string") +</PRE> + +<P>If the message you get doesn't include quotation marks around the +word <CODE>string</CODE>, then do nothing. But if you do see <CODE>"string"</CODE> with +quotation marks, edit <CODE>simply.scm</CODE> and change the definition of +<CODE>error-printform</CODE> to + +<P><PRE>(define (error-printform x) x) +</PRE> + +<P>3. Although the Scheme standard says that the <CODE>read</CODE> +procedure should not read the newline character following an +expression that it reads, some old versions of Scheme get this wrong. + +<P>After loading <CODE>simply.scm</CODE>, do the following experiment: + +<P><PRE>> (read-line) +</PRE> + +<P>End the line with the <CODE>return</CODE> or <CODE>enter</CODE> key +(whichever is appropriate in your version of Scheme) as usual, +but don't type a second <CODE>return</CODE> or <CODE>enter</CODE> yet. If +Scheme prints <CODE>()</CODE> right away, skip this paragraph; your +version of Scheme behaves correctly. If, on the other hand, +nothing happens, type another <CODE>return</CODE> or <CODE>enter</CODE>. In +this case you must edit <CODE>functions.scm</CODE> and remove the +invocation of <CODE>read-line</CODE> on the first line of the body of +the <CODE>functions</CODE> procedure. + +<P>4. There is a substantial loss of efficiency in treating strings of +digits as numbers in some contexts and as text in other contexts. When +we're treating 1024 as text, we want to be able to take its <CODE>butfirst</CODE>, +which should be 024. But in Scheme, <CODE>024</CODE> is the same as <CODE>24</CODE>, so +instead <CODE>butfirst</CODE> returns a string: + +<P><PRE>> (butfirst 1024) +"024" +</PRE> + +<P>Yet we want to be able to do arithmetic on this value: + +<P><PRE>> (+ 3 (butfirst 1024)) +27 +</PRE> + +<P>To accomplish this, we redefine all of Scheme's arithmetic +procedures to accept strings of digits and convert them to numbers. This +redefinition slows down all arithmetic, not just arithmetic on strange +numbers, and it's only rarely important to the programs we write. +Therefore, we've provided a way to turn this part of the package off and on +again. If your programs run too slowly, try saying + +<P><PRE>> (strings-are-numbers #f) +</PRE> + +<P>If you find that some program doesn't work because it tries to do +arithmetic on a digit string and gets an error message, you can say + +<P><PRE>> (strings-are-numbers #t) +</PRE> + +<P>to restore the original behavior of our programs. We recommend +that you leave <CODE>strings-are-numbers</CODE> true while exploring the first few +chapters, so that the behavior of the word data type will be consistent. +When you get to the large example programs, you may want to change to false. + +<P><H2>Loading Our Programs</H2> + +<P>Scheme's <CODE>load</CODE> procedure doesn't scan your entire disk looking for the +file you want to load. Instead, it only looks in one particular directory +(DOS/Unix) or folder (Macintosh/Windows). If you want to load our programs, +you have to make sure that Scheme can find them. + +<P>The first way to accomplish this is to give the full "path" as part of the +argument to <CODE>load</CODE>. Here are some examples:<A NAME="text2" HREF="appendix-running.html#ft2">[2]</A> + +<P><PRE>UNIX-SCHEME> (load "/usr/people/matt/scheme-stuff/simply.scm") + +WINDOWS-SCHEME> (load "c:\\scheme\\simply.scm") + +MAC-SCHEME> (load "Hard Disk:Scheme Folder:simply.scm") +</PRE> + +<P>Under Unix, directories in a path are separated by forward slash +characters. Under Windows and DOS, directories are separated by backward slash +characters, which have a special meaning to +Scheme. So you must use double +backslashes as in our example above. On a Macintosh, you separate the parts of +a path with colons. (However, most versions of Scheme for the Macintosh +or Windows +have a load command in one of the menus that opens a standard file +selection dialog box, so you can use that instead.) + +<P>The other possibility is to put the files in the place where your version of +Scheme looks for them. In many versions of Scheme, <CODE>load</CODE> looks +for files in the folder that contains the Scheme program itself. Put our +files in that folder. + +<P>On Unix, the default loading directory is whatever directory you're in at +the moment. If you want to work on different projects in different +directories, there's no way to make it so that <CODE>load</CODE> will always find +our files. (But see our suggestion about writing <CODE>book-load</CODE>.) + +<P><H2>Versions of Scheme</H2> + +<P>There are lots of them, both free and commercial. Three places to +look for pointers are + +<P><PRE>http://swissnet.ai.mit.edu/scheme-home.html +http://www.schemers.org +http://www.cs.indiana.edu/scheme-repository +</PRE> + +<P>In general, there are four things you should be sure to learn about +whatever version of Scheme you choose: + +<P><P><TABLE><TR><TH align="right" valign="top">•<TD> <TD valign="top">Most versions of Scheme include a <EM>debugger</EM> to help you find +program errors. If you call a primitive with an argument not in +its domain, for example, Scheme will start the debugger, which will have +features to let you find out where in your program the error occurred. +These debuggers vary greatly among versions of Scheme. The first thing +you should learn is how to <EM>leave</EM> the debugger, so you can get +back to a Scheme prompt! + +</TABLE><TABLE><TR><TH align="right" valign="top">•<TD> <TD valign="top">Many versions of Scheme will read an <EM>initialization file</EM> if +you create one. That is, when you start Scheme, it will look for a file +of a particular name (something like <CODE>init.scm</CODE>, but not usually +exactly that), and if there is such a file, Scheme will <CODE>load</CODE> it +automatically. You can copy our <CODE>simply.scm</CODE> file to the proper +filename for your version, and you'll have our added primitives available +every time you start Scheme. + +</TABLE><TABLE><TR><TH align="right" valign="top">•<TD> <TD valign="top">Most versions of Scheme provide a <CODE>trace</CODE> capability, but the +format of the trace results are quite different from one version to +another. + +</TABLE><TABLE><TR><TH align="right" valign="top">•<TD> <TD valign="top">If you are using a Macintosh, one thing to watch out for is that some +versions of Scheme expect you to use the ENTER key at the end of an +expression, while others expect you to use the RETURN key. + +</TABLE> + +<P><H2>Scheme Standards</H2> + +<P>The Web sites listed above will provide the latest version of the <EM>Revised<SUP><SMALL><I>n</I></SMALL></SUP> Report on the Algorithmic Language Scheme.</EM> You can +get the document in either Postscript or HTML format. + +<P>IEEE Standard 1178-1990, <EM>IEEE Standard for the Scheme Programming +Language,</EM> may be ordered from IEEE by calling 1-800-678-IEEE or +908-981-1393 or writing IEEE Service Center, 445 Hoes Lane, P.O. Box 1331, +Piscataway, NJ 08855-1331, and using order number SH14209 ($28 for IEEE +members, $40 for others). ISBN 1-55937-125-0. + +<P> +<HR> +<A NAME="ft1" HREF="appendix-running.html#text1">[1]</A> If you see an error message about "end of file" or "EOF," it +probably means that the file you are trying to load contains unbalanced +parentheses; you have started an expression with a left parenthesis, and the +file ended before Scheme saw a matching right parenthesis.<P> +<A NAME="ft2" HREF="appendix-running.html#text2">[2]</A> Suggestion for +instructors: when we teach this class, we define a procedure like + +<P><PRE>(define (book-load filename) + (load (string-append "/usr/cs3/progs-from-book/" filename))) +</PRE> + +<P>so that students can just say + +<P><PRE>(book-load "functions.scm") +</PRE><P> +<P><A HREF="../ss-toc2.html">(back to Table of Contents)</A><P> +<A HREF="../ssch26/preview.html"><STRONG>BACK</STRONG></A> +chapter thread <A HREF="appendix-cl.html"><STRONG>NEXT</STRONG></A> + +<P> +<ADDRESS> +<A HREF="../index.html">Brian Harvey</A>, +<CODE>bh@cs.berkeley.edu</CODE> +</ADDRESS> +</BODY> +</HTML> |