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1. floivector ref elecd ERE aes flo vector set 2 lo e ev flush purification queue i24 Pr identify world ss ignore assignment traps ignore reference traps inhibit editor init file integrate gcc heist ES tadis integrate external integrate operator jJntersection 6c eee eee eee load noisily eese load oOptiOomn eeeec e Ree N print gc statistics procedure environment 71 sides ants i 51 T 24 18 m 19 72 R reduce operator oiseecg cece eee tae Ra 28 29 replace operator ve ei eebr ebbe federe 27 reset editor EE 56 reset editor windows sess 56 OS Galt wg dae eere Teo hea stare ined Sareea Ee ale 49 S save buffers kill edwin 52 save buffers kill scheme 52 save editor files cee eee 55 Scheme Jnteraction mode 49 scheme m de iiss bodes ave reini orette SEA ys 49 EE 33 set command line parser 10 set gc notification 0 22 SE vat datas piste Ee Eer 24 simple command line parser 9 suspend edwiln cielos ree ed y d ed e 52 suspend scheme c idi Eeer hn 52 system global environment 17 T Loggle gc notificationl 27 PLACE cM m 45 trace bothi eoe rei
2. Typing e creates a new buffer in which you may browse through the current environment In this new buffer you can use the mouse the arrows or C n and C p to select lines and view different environments The environments listed are the same as those in the description buffer If the selected environment structure is too large to display i e if the number of bindings in the environment exceeds the value of the editor variable environment package limit a message to that effect is displayed To display the environment in this case use M x set variable to set environment package limit to 4f At the bottom of the new buffer is a region for evaluating expressions similar to that of the description buffer The appearance of environment displays is controlled by the editor variables debugger show inner frame topmost and debugger compact display which affect the ordering of environment frames and the line spacing respectively Type q to quit the debugger killing its primary buffer any others that it has created and the window that was popped up to show the debugger Note The description buffers created by the debugger are given names beginning with spaces so that they do not appear in the buffer list these buffers are automatically deleted when you quit the debugger If you wish to keep one of these buffers simply rename it using M x rename buffer once it has been renamed it will not be automatically deleted 7 7 Last Resorts When Sc
3. home joe Under Windows the environment variables HOMEDRIVE and HOMEPATH set by the operating system are used instead Under unix HOME is set by the login shell Directory for various temporary files The variables are tried in the given order If none of them is suitable built in defaults are used under unix var tmp usr tmp tmp under Windows temp tmp and V all on the system drive INF_DIRECTORY Directory containing the debugging information files for the Scheme system Should contain subdirectories corresponding to the subdirectories in the source tree For example if its value is f random runtime system debugging files will be expected in f random runtime while Edwin debugging files will be expected in f random edwin By default the information is searched for on the library path LOAD_OPTIONS Specifies the location of the options database file used by the load option procedure The default is optiondb scm on the library path 2 6 3 Environment Variables for Edwin These environment variables are referred to by Edwin EDWIN BINARY DIRECTORY Directory where Edwin expects to find files providing autoloaded facilities The default is edwin on the library path EDWIN INFO DIRECTORY EDWIN ETC ESHELL SHELL PATH Directory where Edwin expects to find files for the info documentation sub system The default is edwin info on t
4. 00 cece eee eee eee es 9 2 6 Environment Variables 0 00 ccc cece eect e ees 10 2 6 1 Environment Variables for the Microcode 10 2 6 2 Environment Variables for the Runtime System 11 2 6 3 Environment Variables for Fdw n es 11 2 6 4 Environment Variables for Microsoft Windows 12 2 7 Starting Scheme from Microsoft Windows 13 2 8 Leaving Scheme 00 0 cece eee eee ens 13 3 Using Scheme 00 cece eens 15 3 1 The Read Eval Print Loop 15 3 1 1 The Prompt and Level Number 15 3 1 2 Interrupting once as rinto Edi E e 16 33 JRestarUlg eeri deeds er i eaat KEE Enia Pa er REE E 16 3 1 4 The Current REPL Environment ky 3 2 Loading Beete rH eee RERO SE 18 5 9 World Images esee ser te RR URS a eere Eh EE 20 3 4 Garbage Collection 20 4 Compiling Programs 23 4 1 Compilation Procedures 0 0 cece cece eens 23 422 Declarations detresse dap eee oe ee pee s 24 4 2 1 Standard Name 25 4 2 2 In line Coding 00 cece eee eee e eee 25 4 2 8 Operator Replacement ccc eee eee eee eee eee 27 4 2 4 Operator HReducton 0 0 c cece een eee eee 28 4 3 Efficiency pe 30 4 3 1 Coding style iiie REENEN NEEN AE ENN NEEN seals 30 4 3 2 Global vanables 0 0 cc ccc cece cece eee enn eees 32 4 9 89 Fixnum arithmetic 0 cece EDE EENE gi eens 34 4 3 4 Flonum anthmetic RR 34 ii MIT GNU Scheme 9
5. To continue call RESTART with an option number RESTART 2 gt Return from BKPT RESTART 1 gt Return to read eval print level 1 2 bkpt gt 3 3 Value 6 2 bkpt gt continue bar Value done pp object output port as code procedure The pp procedure is described in Section Output Procedures in MIT GNU Scheme Reference Manual However since this is a very useful debugging tool we also mention it here pp provides two very useful functions 1 pp will print the source code of a given procedure Often when debugging you will have a procedure object but will not know exactly what procedure it is Printing the procedure using pp will show you the source code which greatly aids identification 2 pp will print the fields of a record structure If you have a compound object pointer print it using pp to see the component fields like this pp gt pathname pathname 14 usr home cph 4 host host 15 device unspecific directory absolute usr home name cph 4j type version unspecific Chapter 5 Debugging 43 When combined with use of the syntax pp provides the functionality of a simple object inspector For example let s look at the fields of the host object from the above example pp 015 4 host 15 type index 0 4 mame Q pa procedure procedure pa prints the arguments of procedure This can be used to remind yourself f
6. If you want to define your own command line options see Section 2 5 Custom Command line Options page 9 Note that MIT GNU Scheme supports only long options that is options specified by verbose names as opposed to short options which are specified by single characters As of release 7 7 90 all options start with two hyphens for compatibility with GNU coding standards and most modern programs Prior to this release options started with a single hyphen While the single hyphen style continues to work it is deprecated and will someday stop working These are the microcode options band filename Specifies the initial world image file band to be loaded Searches for filename in the working directory and the library directories using the full pathname of the first readable file of that name If filename is an absolute pathname on unix this means it starts with then no search occurs filename is tested for readability and then used directly If this option isn t given the filename is the value of the environment variable MITSCHEME_BAND or if that isn t defined all com in these cases the library directories are searched but not the working directory heap blocks Specifies the size of the heap in 1024 word blocks Overrides any default The size specified by this option is incremented by the amount of heap space needed by the band being loaded Consequently heap specifies how much free
7. define factorial n if n 2 1 n factorial n 1 If we stop factorial in the middle of evaluating n 1 the n 1 is at subproblem level 0 Following the history of the computation upwards factorial n 1 is at subproblem level 1 and n factorial n 1 is at subproblem level 2 These ex pressions all have reduction number 0 Continuing upwards the if expression has reduction number 1 Moving backwards in the history of a computation subproblem levels and reduction numbers increase starting from zero at the expression currently being evaluated Reduction numbers increase until the next subproblem where they start over at zero The best way to get a feel for subproblem levels and reduction numbers is to experiment with the debugging tools especially debug 5 2 The Command Line Debugger There are two debuggers available with MIT GNU Scheme One of them runs under Ed win and is described in that section of this document see Section 7 6 Edwin Debugger page 54 The other is command line oriented does not require Edwin and is described here The command line debugger called debug is the tool you should use when Scheme signals an error and you want to find out what caused the error When Scheme signals an error it records all the information necessary to continue running the Scheme program that Chapter 5 Debugging 39 caused the error the debugger provides you with the
8. edit Alternatively you can load Edwin by giving the edwin command line option and then calling the procedure edit edit procedure edwin procedure Enter the Edwin text editor If entering for the first time the editor is initialized by calling create editor with no arguments Otherwise the previously initialized editor is reentered The procedure edwin is an alias for edit inhibit editor init file variable When Edwin is first initialized it loads your init file called edwin under unix edwin ini on PCs if you have one If the Scheme variable inhibit editor init file is true however your init file will not be loaded even if it exists By default this variable is false Note that you can set this variable in your Scheme init file see Section 2 2 Customiz ing Scheme page 5 create editor arg procedure Initializes Edwin or reinitializes it if already initialized create editor is normally invoked automatically by edit If no args are given the value of create editor args is used instead In other words the following are equivalent create editor apply create editor create editor args On the other hand if args are given they are used to update create editor args making the following equivalent apply create editor args begin set create editor args args create editor create editor args variable This variable controls the initialization of Edwin The following va
9. when you call debug to examine compiled code When you load a com file Scheme remembers where it was loaded from and when the debugger or pp looks at the compiled code from that file it attempts to find the bci file in the same directory from which the com file was loaded Thus it is a good idea to leave these files together bci files are stored in a compressed format The debugger has to uncompress the files when it looks at them and on a slow machine this can take a noticeable time The system takes steps to reduce the impact of this behavior debugging information is cached in memory and uncompressed versions of bci files are kept around The default behavior is that a temporary file is created and the bci file is uncompressed into it The temporary file is kept around for a while afterwards and during that time if the uncompressed bci file is needed the temporary file is used Each such reference updates an access time that is associated with the temporary file The garbage collector checks the access times of all such temporary files and deletes any that have not been accessed in five minutes or more All of the temporaries are deleted automatically when the Scheme process is killed Two other behaviors are available One of them uncompresses the bci file each time it is referenced and the other uncompresses the bci file and writes it back out as a bif file The bif f
10. Title Page then add an item describing the Modified Version as stated in the previous sentence Preserve the network location if any given in the Document for public access to a Transparent copy of the Document and likewise the network locations given in the Document for previous versions it was based on These may be placed in the History section You may omit a network location for a work that was published at least four years before the Document itself or if the original publisher of the version it refers to gives permission For any section Entitled Acknowledgements or Dedications Preserve the Title of the section and preserve in the section all the substance and tone of each of the contributor acknowledgements and or dedications given therein Preserve all the Invariant Sections of the Document unaltered in their text and in their titles Section numbers or the equivalent are not considered part of the section titles Delete any section Entitled Endorsements Such a section may not be included in the Modified Version Do not retitle any existing section to be Entitled Endorsements or to conflict in title with any Invariant Section Preserve any Warranty Disclaimers If the Modified Version includes new front matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document you may at your option designate some or all of these sections as invarian
11. bold Allowed characteristics are integer specifying the font size in points and the following style modifiers bold italic regular underline and strikeout You should specify only fixed width fonts as variable width fonts are not drawn correctly Once in Edwin the font can be changed with the set font and set default font commands GEOMETRY Four integers separated by commas or spaces that specify the placement and size of the MIT GNU Scheme window as a left top width height quadruple The units are screen pixels and 1 means allow the system to choose this parameter E g 1 1 500 300 places a 500 by 300 pixel window at some system determined position on the screen The width and height include the window border and title The default value is 1 1 1 1 FOREGROUND A value specifying the window text color The color is specified as hex blue green and red values not RGB e g 0x 0000 for blue BACKGROUND A value specifying the window background color See MITSCHEME_FOREGROUND These variables are used together to indicate the user s home directory This is the preferred way to specify the home directory Specifies the login name of the user running Scheme This is used for several different purposes USERNAME is preferred USER is used if USERNAME is not defined If neither of these variables is defined an error is signalled when the username is required Specifies a dir
12. declaration the compiler cannot recognize any of the common operators and compile them efficiently The usual integrations declaration is usually sufficient to get good quality compiled code If you really need to squeeze more performance out of your code then we hope that you find the following grab bag of tips hints and explanations useful 4 3 1 Coding style Scheme is a rich language in which there are usually several ways to say the same thing A coding style is a set of rules that a programmer uses for choosing an expressive form to use in a given situation Usually these rules are aesthetic but sometimes there are efficiency issues involved this section describes a few choices that have non obvious efficiency consequences Better predicates Consider the following implementation of map as might be found in any introductory book on Scheme Chapter 4 Compiling Programs 31 define map f lst if null 1st ZO cons f car lst map f cdr 1st The problem with this definition is that at the points where car and cdr are called we still do not know that Ist is a pair The compiler must insert a type check or if type checks are disabled the program might give wrong results Since one of the fundamental properties of map is that it transforms lists we should make the relationship between the input pairs and the result pairs more apparent in the code define map f 1st cond pair lst cons f car lst map f c
13. foo in gt usr cph foo out 2 amp 1 E This option is ignored under non unix operating systems nocore Specifies that Scheme should not generate a core dump under any circum stances If this option is not given and Scheme terminates abnormally you will be prompted to decide whether a core dump should be generated This option is ignored under non unix operating systems library path Sets the library search path to path This is a list of directories that is searched to find various library files such as bands If this option is not given the value of the environment variable MITSCHEME_LIBRARY_PATH is used if that isn t defined the default is used On unix the elements of the list are separated by colons and the default value is usr local 1lib mit scheme ARCH On PCs the elements of the list are separated by semicolons and the default value is c local mit scheme fasl filename Specifies that a cold load should be performed using filename as the initial file to be loaded If this option isn t given a normal load is performed instead This option may not be used together with the band option This option is useful only for maintenance and development of the MIT GNU Scheme runtime system The following options are runtime options They are processed after the microcode options and after the image file is loaded no init file This option causes Scheme to ignore the
14. normally bound to C x C z These two commands correspond to the procedures exit and quit respectively e Graphical interface buttons that you can activate Under Windows closing the console window Scheme s main window causes Scheme to be terminated Under any operating 14 MIT GNU Scheme 9 0 system closing an Edwin window causes that window to go away and if it is the only Edwin window it terminates Scheme as well Chapter 3 Using Scheme 15 3 Using Scheme This chapter describes how to use Scheme to evaluate expressions and load programs It also describes how to save custom world images and how to control the garbage collector Subsequent chapters will describe how to use the compiler and how to debug your programs 3 1 The Read Eval Print Loop When you first start up Scheme from the command line you will be typing at a program called the Read Eval Print Loop abbreviated REPL It displays a prompt at the left hand side of the screen whenever it is waiting for input You then type an expression terminating it with RET Scheme evaluates the expression prints the result and gives you another prompt 3 1 1 The Prompt and Level Number The REPL prompt normally has the form 1 gt The 1 in the prompt is a level number which is always a positive integer This number is incremented under certain circumstances the most common being an error For example here is what you will see if you type f o o RET after
15. operating systems Read the section detailing the installation for the operating system that you are using 1 1 Unix Installation We will use as an example the installation for GNU Linux The installation for other unix systems is similar There are several references to ARCH below these refer to the computer architecture that Scheme is compiled for either i386 or x86 64 MIT GNU Scheme is distributed as a compressed tar file The tar file contains both source and binary files the binary files are pre compiled Scheme code for a particular computer architecture In order to install the software it s necessary to configure and compile the C code then to install the combined C and Scheme binaries This is done in the following steps 1 Unpack the tar file mit scheme VERSION ARCH tar gz into the directory mit scheme VERSION For example tar xzf mit scheme 9 0 i386 tar gz will create a new directory mit scheme 9 0 2 Move into the new directory cd mit scheme VERSION src 3 Configure the software configure 4 Build the software make compile microcode 5 Install the software make install After installing the software you can delete the unpacked directory Cd deus rm rf mit scheme VERSION By default the software will be installed in usr local in the subdirectories bin and lib If you want it installed somewhere else for example opt mit scheme pass the
16. prefix option to the configure script as in configure prefix opt mit scheme The configure script accepts all the normal arguments for such scripts and additionally accepts some that are specific to MIT GNU Scheme To see all the possible arguments and their meanings run the command configure help 1 2 Windows Installation This section describes how to install MIT GNU Scheme on Windows 2000 Windows XP Windows Vista or Windows 7 MIT GNU Scheme is distributed as a self installing executable Installation of the soft ware is straightforward Simply execute the downloaded file and answer the installer s 4 MIT GNU Scheme 9 0 questions The installer will allow you to choose the directory in which MIT GNU Scheme is to be installed and the name of the folder in which the shortcuts are to be placed To uninstall the software open up the Control Panel run Add Remove Programs and double click on MIT GNU Scheme Chapter 2 Running Scheme 5 2 Running Scheme This chapter describes how to run MIT GNU Scheme It also describes how you can customize the behavior of MIT GNU Scheme using command line options and environment variables 2 1 Basics of Starting Scheme Under unix MIT GNU Scheme is invoked by typing mit scheme at your operating system s command interpreter Under Windows MIT GNU Scheme is invoked by double clicking on a shortcut In either case Scheme will load itself and print something lik
17. present version but may differ in detail to address new problems or concerns See http www gnu org copyleft Each version of the License is given a distinguishing version number If the Document specifies that a particular numbered version of this License or any later version applies to it you have the option of following the terms and conditions either of that specified version or of any later version that has been published not as a draft by the Free Software Foundation If the Document does not specify a version number of this License you may choose any version ever published not as a draft by the Free Software Foundation Appendix B GNU Free Documentation License 65 B 1 ADDENDUM How to use this License for your documents To use this License in a document you have written include a copy of the License in the document and put the following copyright and license notices just after the title page Copyright C year your name Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 2 or any later version published by the Free Software Foundation with no Invariant Sections no Front Cover Texts and no Back Cover Texts A copy of the license is included in the section entitled GNU Free Documentation License If you have Invariant Sections Front Cover Texts and Back Cover Texts replace the with Texts line with this
18. space will be available in the heap when Scheme starts independent of the amount of heap already consumed by the band constant blocks Specifies the size of constant space in 1024 word blocks Overrides any default Constant space holds the compiled code for the runtime system and other sub systems stack blocks Specifies the size of the stack in 1024 word blocks Overrides any default This is Scheme s stack not the unix stack used by C programs 8 MIT GNU Scheme 9 0 option summary Causes Scheme to write an option summary to standard error This shows the values of all of the settable microcode option variables emacs Specifies that Scheme is running as a subprocess of GNU Emacs This option is automatically supplied by GNU Emacs and should not be given under other circumstances interactive If this option isn t specified and Scheme s standard I O is not a terminal Scheme will detach itself from its controlling terminal which prevents it from getting signals sent to the process group of that terminal If this option is specified Scheme will not detach itself from the controlling terminal This detaching behavior is useful for running Scheme as a background job For example using Bourne shell the following will run Scheme as a background job redirecting its input and output to files and preventing it from being killed by keyboard interrupts or by logging out mit scheme lt usr cph
19. specifies whether name associates to the right or left e The null value option specifies a value to use in the following cases none empty When no arguments are supplied to name value is returned one single When a single argument is provided to name value becomes the second argument to binop any always binop is used on the last argument and value provides the remain ing argument to binop In the above options when value is supplied to binop it is supplied on the left if grouping to the left otherwise it is supplied on the right e The singleton option specifies a function unop to be invoked on the single argument given This option supersedes the null value option which can only take the value none e The wrapper option specifies a function wrap to be invoked on the result of the outermost call to binop after the expansion If n is provided it must be a non negative integer indicating a number of arguments that are transferred verbatim from the original call to the wrapper They are passed to the left of the reduction e The maximum option specifies that calls with more than m arguments should not be reduced 4 3 Efficiency Tips How you write your programs can have a large impact on how efficiently the compiled program runs The most important thing to do after choosing suitable data structures is to put the following declaration near the beginning of the file declare usual integrations Without this
20. starting Scheme Unbound variable foo To continue call RESTART with an option number RESTART 3 gt Specify a value to use instead of foo RESTART 2 gt Define foo to a given value RESTART 1 gt Return to read eval print level 1 2 error In this case the level number has been incremented to 2 which indicates that a new REPL has been started also the prompt string has been changed to remind you that the REPL was started because of an error The 2 means that this new REPL is over the old one The original REPL still exists and is waiting for you to return to it for example by entering restart 1 Furthermore if an error occurs while you are in this REPL yet another REPL will be started and the level number will be increased to 3 This can continue ad infinitum but normally it is rare to use more than a few levels The normal way to get out of an error REPL and back to the top level REPL is to use the C g interrupt This is a single keystroke command executed by holding down the CTRL key and pressing the G key C g always terminates whatever is running and returns you to the top level REPL immediately Note The appearance of the error gt prompt does not mean that Scheme is in some weird inconsistent state that you should avoid It is merely a reminder that your program was in error an illegal operation was attempted but it was detected and avoided Often the best way
21. the runtime system for compression of compiled code debugging information format The format procedure See Section Format in MIT GNU Scheme Ref erence Manual gdbm Support to access gdbm databases Undocumented see the source files runtime gdbm scm and microcode prgdbm c ordered vector Support to search and do completion on vectors of ordered elements Undocumented see the source file runtime ordvec scm rb tree The red black tree data type See Section Red Black Trees in MIT GNU Scheme Reference Manual regular expression Support to search and match strings for regular expressions See Section Regular Expressions in MIT GNU Scheme Reference Manual stepper Support to step through the evaluation of Scheme expressions Undoc umented see the source file runtime ystep scm Used by the Edwin command step expression subprocess Support to run other programs as subprocesses of the Scheme process Undocumented see the source file runtime process scm Used exten sively by Edwin synchronous subprocess Support to run synchronous subprocesses See Section Subprocesses in MIT GNU Scheme Reference Manual wt tree The weight balanced tree data type See Section Weight Balanced Trees in MIT GNU Scheme Reference Manual In addition to the built in options you may define other options to be loaded by load options by modifying the file optiondb scm on the library path
22. this history The command M p moves backwards through the history inserting previously evaluated expressions at point Like wise M n moves forward through the history The commands C c C r and C c C s search backward and forward through the history for a particular string The command C c C o deletes any output from the previous evaluation use this command with care since it cannot be undone The command C c C 1 finds the most recent expression in the buffer and moves point there When an expression that you evaluate signals an error the REPL buffer notices this and offers to run the debugger for you Answer this question with a y or n response You can start the debugger whenever the REPL buffer is listening by executing the C c C d command In either case this starts the Edwin debugger which pops up a new window containing the debugger Your REPL buffer remains in the error state allowing you to examine it further if you wish 7 6 The Edwin Debugger The Edwin debugger is similar to the command line debugger except that it takes advantage of multiple windows and Edwin s command structure to provide a more intuitive interface The debugger operates as a browser much like Dired presenting you with an overview of the subproblem structure and allowing you to examine parts of that structure in more detail by selecting the parts When started the debugger creates a buffer debug showing the subproblem structure and select
23. when an error has occurred and you are not in the top level REPL the constant 4f Just like 4t except that the runtime system will not perform normal restart initializations in particular it will not load your init file To restore a saved band give the band option when starting Scheme Alternatively evaluate disk restore filename which will destroy the current world replacing it with the saved world The argument to disk restore may be omitted in which case it defaults to the filename from which the current world was last restored 3 4 Garbage Collection This section describes procedures that control garbage collection See Section 2 3 Memory Usage page 6 for a discussion of how MIT GNU Scheme uses memory gc flip safety margin procedure Forces a garbage collection to occur Returns the number of words of storage available after collection an exact non negative integer Safety margin determines the number of words of storage available to system tasks after the need for a garbage collection is detected and before the garbage collector is started An example of such a system task is changing the run light to show gc when scheme is running under Emacs Note well that you should not specify safety margin unless you know what you are doing If you specify a value that is too small you can put Scheme in an unusable state Chapter 3 Using Scheme 21 purify object pure space queue procedure Mo
24. will reinitialize the editor C x C z Stop Edwin and suspend Scheme returning control to the operating system s command interpreter suspend scheme When Scheme is resumed using the command interpreter s job control commands Edwin is automatically restarted where it was stopped This command is identical to the C x C z command of GNU Emacs C x C c Offer to save any modified buffers then kill both Edwin and Scheme save buffers kill scheme Control is returned to the operating system s com mand interpreter and the Scheme process is terminated This command is identical to the C x C c command of GNU Emacs 7 3 Scheme Mode As you might expect Edwin has special support for editing and evaluating Scheme code This section describes Scheme Mode the appropriate mode for editing MIT GNU Scheme programs Scheme mode is normally entered automatically by visiting a file whose file name ends in scm You can also mark a file as Scheme code by placing the string Scheme on the first line of the file Finally you can put any buffer in Scheme mode by executing the command M x scheme mode Scheme mode is similar to the Emacs modes that edit Lisp code So for example C i indents the current line and C M q indents the expression to the right of point The close Chapter 7 Edwin 53 parenthesis will temporarily flash the matching open parenthesis Most Scheme constructs requiring special indentation are recognized by Scheme m
25. you include in the combination all of the Invariant Sections of all of the original documents unmodified and list them all as Invariant Sections of your combined work in its license notice and that you preserve all their Warranty Disclaimers The combined work need only contain one copy of this License and multiple identical Invariant Sections may be replaced with a single copy If there are multiple Invariant Sections with the same name but different contents make the title of each such section unique by adding at the end of it in parentheses the name of the original author or publisher of that section if known or else a unique number Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work In the combination you must combine any sections Entitled History in the vari ous original documents forming one section Entitled History likewise combine any sections Entitled Acknowledgements and any sections Entitled Dedications You must delete all sections Entitled Endorsements 6 COLLECTIONS OF DOCUMENTS You may make a collection consisting of the Document and other documents released under this License and replace the individual copies of this License in the various documents with a single copy that is included in the collection provided that you follow the rules of this License for verbatim copying of each of the documents in all other respe
26. 0 5 Debugging w AE EA P OR ebat 37 5 1 Subproblems and Reductions 0 0 00 e eee eees 38 5 2 The Command Line Debugger 0 00 cece eee ee ees 38 5 3 Debugging Aids 4 244 oci ceo beate EP ERT ENEG Ee e 41 5 4 Advising Procedures 0 000 c cece eee eese 44 6 GNU Emacs Interface 49 T E EEN 51 ol Starting Edwini us iie d E RE beerebrer REST ses ol 7 2 Leaving dein 52 3 Scheme Modes scoop thee S Se bebe eh PRIM 52 TA FivaltiatiOny lt 1 sce 226 secre os ph Seen P RE een E ESNIE 53 T5 REPL Mode ENNEN EN eke eis sad REENEN EENS aes 53 7 6 The Edwin Debugger 00 c cece eee eee eens 54 ot hast Resor serait nant Seared e Se oa Gta hh ee a 55 Appendix A Release Notes 57 Appendix B GNU Free Documentation License EEN 59 B 1 ADDENDUM How to use this License for your documents 65 Appendix C Environment variable Index 67 Appendix D Option Index 69 Appendix E Variable Index 71 Appendix F Concept Index 73 Introduction 1 Introduction This document describes how to install and use MIT GNU Scheme the UnCommon Lisp It gives installation instructions for all of the platforms that we support complete documen tation of the command line options and environment variables that control how Scheme works and rudimentary descriptions of how to interact with the evaluator compile and debug
27. 2 3 map 3 Replacements map f x yz o map f x y z map f x y map 3 f x y map f x map 2 f x map f map f map map Presumably map 2 and map 3 are efficient versions of map that are written for exactly two and three arguments respectively All the other cases are not expanded but are handled by the original general map procedure which is less efficient because it must handle a variable number of arguments replace operator name declaration The syntax of this declaration is replace operator name nargs1 value1 nargs2 value2 ES E where e name is a symbol e nargsl nargs2 etc are non negative integers or one of the following symbols any else or otherwise e valuel value2 etc are simple expressions in one of these forms gt constant A constant variable A variable primitive primitive name arity The primitive procedure named primitive name The optional ele ment arity a non negative integer specifies the number of arguments that the primitive accepts global var A global variable The meanings of these fields are e name is the name of the operator to be reduced If is is not shadowed for example by a let then it may be replaced according to the following rules 28 MIT GNU Scheme 9 0 e If the operator has nargsN arguments then it is replaced with a call to valueN with the same arguments e If the number of arguments is not listed and one of the n
28. 8 MIT GNU Scheme 9 0 5 1 Subproblems and Reductions Understanding the concepts of reduction and subproblem is essential to good use of the debugging tools The Scheme interpreter evaluates an expression by reducing it to a simpler expression In general Scheme s evaluation rules designate that evaluation proceeds from one expression to the next by either starting to work on a subexpression of the given expression or by reducing the entire expression to a new simpler or reduced form Thus a history of the successive forms processed during the evaluation of an expression will show a sequence of subproblems where each subproblem may consist of a sequence of reductions For example both 5 6 and 7 9 are subproblems of the following combination x 5 6 7 9 If prime n is true then cons prime n is a reduction for the following expression if prime n cons prime n cons not prime n This is because the entire subproblem of the if expression can be reduced to the problem cons prime n once we know that prime n is true the cons not prime n can be ignored because it will never be needed On the other hand if prime n were false then cons not prime n would be the reduction for the if expression The subproblem level is a number representing how far back in the history of the current computation a particular evaluation is Consider factorial
29. An example file is included with the distribution normally this file consists of a series of calls to the procedure define load option terminated by the expression further load options standard load options 20 MIT GNU Scheme 9 0 define load option symbol thunk procedure Each thunk must be a procedure of no arguments Defines the load option named symbol When the procedure load option is called with symbol as an argument the thunk arguments are executed in order from left to right 3 3 World Images A world image also called a band is a file that contains a complete Scheme system perhaps additionally including user application code Scheme provides a method for saving and restoring world images The method writes a file containing all of the Scheme code and data in the running process The file runtime com that is loaded by the microcode is just such a band To make your own band use the procedure disk save disk save filename identify procedure Causes a band to be written to the file specified by filename The optional argument identify controls what happens when that band is restored as follows not specified Start up in the top level REPL identifying the world in the normal way a string Do the same thing except print that string instead of Scheme when restarting the constant t Restart exactly where you were when the call to disk save was per formed This is especially useful for saving your state
30. EE 34 flonumMCONSING EEN EE NEE EES A 34 tel CEET 12 H heap EE 6 ehre eien e BS 43 I EIERE E E E D Se 6 MN EE 5 inspecting environments 000 43 integrations seeing effects of 26 L level number REPL uessss 15 49 M Me Enn deeg OPES EUR RR doe dede 49 74 n EE 49 MEMO Y EE ds ta KEE EE EES EN D microcode version 5 P lg 1 procedures finding ccc eee eee ee 43 prompt REEL ere neenon ses 15 R reduction e ENEE EE eb eee 38 reference Lrapne eee eee eee ere 32 release number 5 IN DEER 15 REPL restarting from kg reporting Dugg 0 cece e eee eee eee eee 1 runtime system Version 00 eee eee 5 S DE version s s dame AREE T REES KERKREG 5 MIT GNU Scheme 9 0 Stack Spaeeue serra vats tiene erp Ru OPER Shanes 6 student package version 5 subexpressiOD AEN eek eee E EEN et ent 38 subproblem noce SEENEN EE 38 subsystem version 5 variable caches 00 c ccc cece eee eae 32 version numbers 0 0 eee eee ees 5 W WebSites 5b oeque Oso ESOS Dade ne window leg reete ora be ure aGeeds oh 12 window position 12 Windowsy 5 abuses tero mee see RET S Vei qe 1 working directory eee 19 world Image 7 20
31. ERDIRB EE RI Re ERROR ENEE 12 USERNAME dE dE tenata AE be i 12 Appendix D Option Index 69 Appendix D Option Index xri dacs T gel D eh EE 8 SE ME EE 9 S601 p auae a xad axe Gece RR REPERI E 9 no init file ese esses 8 SH EE 8 49 malo MED 8 CeOVAlos2usssv ere x P PIEPC UT ERE ERE US 9 EE Ee 8 heap csse e ees T Sitack pecs aciced omer XUPPHeXG PX V EEUPEDO 7 Appendix E Variable Index Appendix E Variable Index KEE 46 dE 46 EE 46 save uncompressed files 23 uncompressed file lifetime 24 A advice eneniibcec eee 47 adyise entry EEN 46 ET Ve GE 47 E DEE 33 APLOPOS EE 43 argument command line parser 9 asslIgned i1lecds 4 be e kx Rb R4 da beds bx dede 33 Lt EE 42 DOWUnd ii Sa tae nn ares gre de die enone d dct Semana n 33 break EE 46 Le e EE 46 break cntry EE 45 break 6xi tii bes SA ua e p HEN ERES 46 EE 19 EE 23 cmdl interrupt abort nearest 16 cmdl interrupt abort previous 16 cmdl interrupt abort top level 16 contine elias hihi Gotan ane tere a Bara ae ean teas 16 EE 51 create editor argS EE EEN ES 51 D G T 38 TEE 25 define integrable c ccicrerre eee ee eee 25 define load 0pti0n enee Ee 20 difference EEN 33 disk restobB6 B vob OPol peers E eds 20 diSk 8Sa8V6 ecu a rer Re addu qua dre nra d 20 F flo vector cons i ecce ever ed flo vector length
32. Gx OO llLneserenhbreer Rege 4e rate sede 52 Gx EE 49 E EE 52 n EE 52 command scripte 00 eee cece eee eee eee 5 command line debugger sssrrrrerurrrer 38 command line option 5 compatibility package version 5 compiler version 5 Constant Spa EE ere e tee eds eee ete es 6 continuation Browser 38 current REPL environment ei D GET EE 38 Debugger command 7 41 Debugger command a 40 Debugger command bh 40 Debugger commande 40 Debugger command d 40 Debugger commande 40 Debugger commande 40 Debugger commande 40 Debugger command bh 40 Debugger commande 41 73 Debugger commande 41 Debugger command ke 41 Debugger command l esesessu 40 Debugger command mm 41 Debugger command o 40 Debugger command pe 40 Debugger command o 41 Debugger command rr 40 Debugger commande 40 Debugger commande 40 Debugger command vu 40 Debugger commande 40 Debugger command w e 40 Debugger commande 41 Debugger command wv 41 Debugger command ze 41 GEbUSEING dee hel D PERIERE hias eg 37 declarations 0 ieres eee eee eee eee 24 E Edwin version 5 environments eamiming 008s 43 EE A A v deeper DROP du ale Seas 37 examining environments 0 000 reo 43 execution history 02 eee e eee eee eee 39 F FDL GNU Free Documentation License 59 finding procedures ss ssrsrrrrrrrrrrerr 43 Dm defi ep t AE EE
33. HOME scheme init or scheme ini file normally loaded automatically when Scheme starts if it exists Chapter 2 Running Scheme 9 suspend file Under some circumstances Scheme can write out a file called scheme_suspend in the user s home directory This file is a world image containing the complete state of the Scheme process restoring this file continues the computation that Scheme was performing at the time the file was written Normally this file is never written but the suspend file option enables writing of this file eval expression This option causes Scheme to evaluate the expressions following it on the com mand line up to but not including the next argument that starts with a hyphen The expressions are evaluated in the user initial environment Unless explicitly handled errors during evaluation are silently ignored load file This option causes Scheme to load the files or lists of files following it on the command line up to but not including the next argument that starts with a hyphen The files are loaded in the user initial environment Unless explicitly handled errors during loading are silently ignored The following option is supported only when Edwin is loaded edit This option causes Edwin to start immediately when Scheme is started 2 5 Custom Command line Options MIT GNU Scheme provides a mechanism for you to define your own command lin
34. MIT GNU Scheme User s Manual Edition 1 93 for MIT GNU Scheme 9 0 2010 02 18 by Stephen Adams Chris Hanson and the MIT Scheme Team This manual documents the use of MIT GNU Scheme 9 0 Copyright 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Massachusetts Institute of Technology Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 2 or any later version published by the Free Software Foundation with no Invariant Sections with the Front Cover Texts being A GNU Manual and with the Back Cover Texts as in a below A copy of the license is included in the section entitled GNU Free Documentation License a The FSF s Back Cover Text is You have freedom to copy and modify this GNU Manual like GNU software Copies published by the Free Software Foundation raise funds for GNU development Table of Contents Introduction ae SEA x mde deve aor Ee a doa M e gg 1 E EE e TE EE 3 1 1 Unix Installaton E E 3 1 2 Windows Installation 0 000 c cece cee nent ences 3 2 Running Scheme 000 eee 5 2 1 Basics of Starting Scheme 0 000 c cece eee eee eee ee 5 2 2 Customizing Scheme 0 0 cece eee aa ne D 2 8 Memory Usage 6 2 4 Command Line Options eene 1 2 5 Custom Command line Options
35. SR1 SIGHUP or SIGPWR signals Under other operating systems this file is never written 10 MIT GNU Scheme 9 0 Multiple if true says that keyword may be followed by more than one argument on the command line In this case procedure is called once for each argument that follows keyword and does not start with a hyphen If multiple is f procedure is called once with the command line argument following keyword In this case it does not matter if the following argument starts with a hyphen set command line parser keyword procedure procedure This low level procedure defines keyword to be a command line option that is defined by procedure When keyword is seen procedure is called with all of the command line arguments starting with keyword as a single list argument Procedure must return two values using the values procedure the unused command line arguments as a list and a thunk that is executed to implement the behavior of the option 2 6 Environment Variables Scheme refers to many environment variables This section lists these variables and de scribes how each is used The environment variables are organized according to the parts of MIT GNU Scheme that they affect Environment variables that affect the microcode must be defined before you start Scheme under unix or Windows others can be defined or overwritten within Scheme by using the set environment variable procedure e g set environment variabl
36. argsN is any else or otherwise then the operation is replaced with a call to the corresponding valueN Only one of the nargsN may be of this form e If the number of arguments is not listed and none of the nargsN is any else or otherwise then the operation is not replaced 4 2 4 Operator Reduction The reduce operator declaration is provided to inform the compiler that certain names are n ary versions of binary operators Here are some examples Declaration declare reduce operator cons cons Replacements cons x y z w cons x cons y cons z w cons x y cons x y cons x x cons ferror too few arguments Declaration declare reduce operator list cons null value any Replacements list x y z w cons x cons y cons z cons w list x y cons x cons y list x cons x list O Declaration declare reduce operator null value O single group left Replacements xy zw O h O x y z w xy o x y x r 0 x Go ta 0 Declaration declare reduce operator 4 null value 0 none group right Replacements x yZzw r ht x Gy ht z w x y r x y ER x Ee sae 0 Note This declaration does not cause an appropriate definition of in the last ex ample to appear in your code It merely informs the compiler that certain optimizations can be performed on calls to by re
37. bal environment will not be shadowed by other definitions when the program is loaded If you redefine some global name in your code for example car cdr and cons you should indicate it in the declaration declare usual integrations car cdr cons You can obtain an alphabetically sorted list of the names that the usual integrations declaration affects by evaluating the following expression eval sort append usual integrations constant names usual integrations expansion names lambda x y string lt symbol gt string x symbol gt string y gt environment scode optimizer 4 2 2 In line Coding Another useful facility is the ability to in line code procedure definitions In fact the compiler will perform full beta conversion with automatic renaming if you request it Here are the relevant declarations integrate name declaration The variables names must be defined in the same file as this declaration Any reference to one of the named variables that appears in the same block as the declaration or one of its descendant blocks will be replaced by the corresponding binding s value expression integrate operator name declaration Similar to the integrate declaration except that it only substitutes for references that appear in the operator position of a combination All other references are ignored integrate external filename declaration Causes the compiler to use the top level integrations pro
38. bda or let These frames collectively represent the block structure of a given environment Once an environment frame is selected by the debugger it is possible to select the parent frame of that frame in other words the enclosing block using the p command You can subsequently return to the original child frame using the s command The s command works because the p command keeps track of the frames that you step through as you move up the environment hierarchy the s command just retraces the path of saved frames Note that selecting a frame using p or s will print the bindings of the newly selected frame Examining environments The following commands allow you to examine the contents of the selected frame The c command prints the bindings of the current frame The a com mand prints the bindings of the current frame and each of its ancestor frames The e command enters a read eval print loop in the selected environment frame expressions typed at that REPL will be evaluated in the selected environment Chapter 5 Debugging 41 To exit the REPL and return to the debugger evaluate abort gt previous or use restart The v command prompts for a single expression and evalu ates it in the selected environment The w command invokes the environment inspector where quitting the environment inspector returns to the debugger Finally the o command pretty prints the procedure that was called to create the selected environment frame C
39. claration tells the compiler that it need not check for reference trap objects when referring to the given variables If any of the variables is unbound or unassigned then a variable reference will yield a reference trap object rather than signaling an error This declaration is relatively safe the worst that can happen is that a reference trap object finds its way into a data structure e g a list or into interpreted code in which case it will probably cause some unrelated variable to mysteriously become unbound or unassigned ignore assignment traps variables declaration This declaration tells the compiler that it need not check for reference trap objects when assigning to the given variables An assignment to a variable that ignores assignment traps can cause a great deal of trouble If there is a compiled procedure call anywhere in the system to this variable the execute caches will not be updated causing an inconsistency between the value used for the procedure call and the value seen by reading the variable This mischief is compounded by the fact that the assignment can cause other assignments that were compiled with checks to behave this way too The variables are specified with expressions from the following set language set name variable specification All of the explicitly listed names all variable specification none variable specification free variable specification bound variable specification assigned va
40. cts You may extract a single document from such a collection and distribute it individu ally under this License provided you insert a copy of this License into the extracted document and follow this License in all other respects regarding verbatim copying of that document 7 AGGREGATION WITH INDEPENDENT WORKS A compilation of the Document or its derivatives with other separate and independent documents or works in or on a volume of a storage or distribution medium is called 64 10 MIT GNU Scheme 9 0 an aggregate if the copyright resulting from the compilation is not used to limit the legal rights of the compilation s users beyond what the individual works permit When the Document is included an aggregate this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document If the Cover Text requirement of section 3 is applicable to these copies of the Document then if the Document is less than one half of the entire aggregate the Document s Cover Texts may be placed on covers that bracket the Document within the aggregate or the electronic equivalent of covers if the Document is in electronic form Otherwise they must appear on printed covers that bracket the whole aggregate TRANSLATION Translation is considered a kind of modification so you may distribute translations of the Document under the terms of section 4 Replacing Invariant Sections with translations r
41. down to newer points in time The g command allows you to select a subproblem by number and the h command will show you a brief summary of all of the subproblems Traversing reductions If the subproblem description says that The execution history for this subproblem contains N reductions then there is a rib of reductions for this subproblem You can see a summary of the reductions for this subproblem using the r command You can move to the next reduction using the b command this moves you to the next older reduction The f command moves in the opposite direction to newer reductions If you are at the oldest reduction for a given subproblem and use the b command you will move to the next older subproblem Likewise if you are at the newest reduction and use f you ll move to the next newer subproblem Examining subproblems and reductions The following commands will show you additional information about the cur rently selected subproblem or reduction The t command will reprint the stan dard description in case it has scrolled off the screen The 1 command will pretty print using pp the subproblem s expression Traversing environments Nearly all subproblems and all reductions have associated environments Select ing a subproblem or reduction also selects the associated environment However environments are structured as a sequence of frames where each frame corre sponds to a block of environment variables as bound by lam
42. dr 1st null 1st 0 else error Not a proper list 1st Note also that the pair case comes first because we expect that map will be called on lists which have on average length greater that one Internal procedures Calls to internal procedures are faster than calls to global procedures T here are two things that make internal procedures faster First the procedure call is compiled to a direct jump to a known location which is more efficient that jumping via a global binding Second there is knock on effect since the compiler can see the internal procedure the compiler can analyze it and possibly produce better code for other expressions in the body of the loop too define map f original 1st let walk 1st original 1st cond pair 1st cons f car lst walk cdr 1st null lst O else error Not a proper list original lst Internal defines Internal definitions are a useful tool for structuring larger procedures However certain in ternal definitions can thwart compiler optimizations Consider the following two procedures where compute 100 is some unknown procedure that we just know returns 100 define f1 define v 100 lambda v define f2 define v compute 100 lambda v 22 MIT GNU Scheme 9 0 The procedure returned by f1 will always give the same result and the compiler can prove this The procedure returned by f2 may return different results
43. e EDWIN_FOREGROUND 32 2 6 1 Environment Variables for the Microcode These environment variables are referred to by the microcode the executable C program called mit scheme under unix and mit scheme exe on the PC MITSCHEME_BAND The initial band to be loaded The default value is all com MITSCHEME_LIBRARY_PATH A list of directories These directories are searched left to right to find bands and various other files On unix systems the list is colon separated with the default usr local lib mit scheme ARCH On PC systems the list is semicolon separated with the default c local mit scheme MITSCHEME_CONSTANT The size of constant space in 1024 word blocks overridden by constant The default value is computed to be the correct size for the band being loaded MITSCHEME_HEAP The size of the heap in 1024 word blocks overridden by heap The default value depends on the architecture for 32 bit machines the default is 4096 and for 64 bit machines the default is 16384 MITSCHEME_STACK The size of the stack in 1024 word blocks overridden by stack The default value is 128 Chapter 2 Running Scheme 11 2 6 2 Environment Variables for the Runtime System These environment variables are referred to by the runtime system HOME HOMEDRIVE HOMEPATH TMPDIR TEMP TMP MITSCHEME_ MITSCHEME_ Directory in which to look for init files E g c users joe or
44. e options This is done by registering handlers to identify particular named options and to process them when Scheme starts Unfortunately because of the way this mechanism is implemented you must define the options and then save a world image containing your definitions see Section 3 3 World Images page 20 Later when you start Scheme using that world image your options will be recognized The following procedures define command line parsers In each the argument keyword defines the option that will be recognized on the command line The keyword must be a string containing at least one character do not include the leading hyphens simple command line parser keyword thunk help procedure Defines keyword to be a simple command line option When this keyword is seen on the command line it causes thunk to be executed Help when provided should be a string describing the option in the help output argument command line parser keyword multiple procedure help procedure Defines keyword to be a command line option that is followed by one or more command line arguments Procedure is a procedure that accepts one argument when keyword is seen it is called once for each argument Help when provided should be a string describing the option It is included in the help output When not provided help will say something lame about your command line option 1 Under unix this file is written when Scheme is terminated by the SIGU
45. e send region C x C e Evaluates the expression to the left of point xscheme send previous expression This is also bound to M RET C c C s Selects the scheme buffer and places you at its end xscheme select process buffer C c C y Yanks the most recently evaluated expression placing it at point xscheme yank previous send This works only in the scheme buffer 50 MIT GNU Scheme 9 0 The following commands provide interrupt capability C c C c C c C x C c C u C c C b C c C p Like typing C g when running Scheme without Emacs xscheme send control g interrupt Like typing C c C x when running Scheme without Emacs xscheme send control x interrupt Like typing C c C u when running Scheme without Emacs xscheme send control u interrupt Like typing C c C b when running Scheme without Emacs xscheme send breakpoint interrupt Like evaluating continue xscheme send proceed Chapter 7 Edwin 51 7 Edwin This chapter describes how to start Edwin the MIT GNU Scheme text editor Edwin is very similar to GNU Emacs you should refer to the GNU Emacs manual for information about Edwin s commands and key bindings except that Edwin s extension language is MIT GNU Scheme while GNU Emacs extensions are written in Emacs Lisp This manual does not discuss customization of Edwin 7 1 Starting Edwin To use Edwin start Scheme with the following command line options mit scheme
46. e this Copyright C 2010 Massachusetts Institute of Technology This is free software see the source for copying conditions There is NO warranty not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE Image saved on Monday February 1 2010 at 12 26 59 AM Release 9 0 Microcode 15 1 Runtime 15 7 SF 4 41 LIAR x86 64 4 118 Edwin 3 116 This information which can be printed again by evaluating identify world tells you the following version information Release is the release number for the entire Scheme system This number is changed each time a new version of Scheme is released Microcode is the version number for the part of the system that is written in C Runtime is the version number for the part of the system that is written in Scheme Following this there may be additional version numbers for specific subsystems SF refers to the scode optimization program sf LIAR ARCH is the native code compiler where ARCH is the native code architecture it compiles to Edwin is the Emacs like text editor There are other subsystems you can load that will add themselves to this list 2 2 Customizing Scheme You can customize your setup by using a variety of tools e Command line options Many parameters like memory usage and the location of libraries may be varied by command line options See Section 2 4 Command Line Options page 7 e Command scripts or batch files You might like
47. ectory that contains the home directories of users One of the places in which Scheme looks for the user s home directory by searching for a subdirectory with the user s login name Chapter 2 Running Scheme 13 2 7 Starting Scheme from Microsoft Windows The Microsoft Windows version of MIT GNU Scheme runs as a graphics based application Scheme is normally started using shortcuts the installer automatically generates several different predefined shortcuts for your convenience The rest of this section gives some tips on how to set up shortcuts that run Scheme If you are unfamiliar with this concept you should read about it in the system help e Under Windows shortcuts can be common or personal When setting common short cuts it is important to make the shortcut properties independent of the vagaries of the environment of the user who is running them e Give the shortcut an accurate Description e Use an absolute pathname to mit scheme exe in the shortcut Command line e If you specify the library command line option then you do not have to worry about the MITSCHEME_LIBRARY_PATH environment variable e Set the shortcut s Working Directory to something sensible On Windows you can use HOMEDRIVE HOMEPATHY to make Scheme start up in the user s home directory e There are several icons available in the Scheme executable choose one that best rep resents the options given on the command line e If you want the sh
48. editors or for images com posed of pixels generic paint programs or for drawings some widely available drawing editor and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters A copy made in an otherwise Transparent file format whose markup or absence of markup has been arranged to thwart or discourage subsequent modification by readers is not Transparent An image format is not Transparent if used for any substantial amount of text A copy that is not Transparent is called Opaque Examples of suitable formats for Transparent copies include plain ASCII without markup Texinfo input format LaTEX input format SGML or XML using a publicly available DTD and standard conforming simple HTML PostScript or PDF designed for human modification Examples of transparent image formats include PNG XCF and JPG Opaque formats include proprietary formats that can be read and edited only by proprietary word processors SGML or XML for which the DTD and or processing tools are not generally available and the machine generated HTML PostScript or PDF produced by some word processors for output purposes only The Title Page means for a printed book the title page itself plus such following pages as are needed to hold legibly the material this License requires to appear in the title page For works in formats which do not have any title page as such Ti
49. ents can be accessed by calling the procedures proc and args respectively Use restart or continue to continue from a breakpoint 46 MIT GNU Scheme 9 0 break exit procedure procedure Like trace exit except that a breakpoint is entered just prior to leaving procedure Procedure its arguments and the result can be accessed by calling the procedures proc args and result respectively Use restart or continue to continue from a breakpoint break both procedure procedure break procedure procedure Sets a breakpoint at the beginning and end of procedure This is break entry and break exit combined unbreak procedure procedure Discontinues the entering of a breakpoint on the entry to and exit from procedure If procedure is not given the default is all breakpointed procedures unbreak entry procedure procedure Discontinues the entering of a breakpoint on the entry to procedure If procedure is not given the default is all entry breakpointed procedures unbreak exit procedure procedure Discontinues the entering of a breakpoint on the exit from procedure If procedure is not given the default is all exit breakpointed procedures The following three procedures are valid only within the dynamic extent of a breakpoint In other words don t call them unless you are stopped inside a breakpoint proc procedure Returns the procedure in which the breakpoint has stopped args procedure Returns the argum
50. ents to the procedure in which the breakpoint has stopped The arguments are returned as a newly allocated list result procedure Returns the result yielded by the procedure in which the breakpoint has stopped This is valid only when in an exit breakpoint The following procedures install advice procedures that are called when the advised procedure is entered or exited An entry advice procedure must accept three arguments the advised procedure a list of the advised procedure s arguments and the advised proce dure s application environment that is the environment in which the procedure s formal parameters are bound An exit advice procedure must accept four arguments the advised procedure a list of the advised procedure s arguments the result yielded by the advised procedure and the advised procedure s application environment Note that the trace and breakpoint procedures described above are all implemented by means of the more general advice procedures so removing advice from an advised procedure will also remove traces and breakpoints advise entry procedure advice procedure Advice must be an entry advice procedure Advice is attached to procedure so that whenever procedure is entered advice is called Chapter 5 Debugging 4T advise exit procedure advice procedure Advice must be an exit advice procedure Advice is attached to procedure so that whenever procedure returns advice is called advice procedure proced
51. equires special permission from their copyright holders but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections You may include a translation of this License and all the license notices in the Document and any Warrany Disclaimers provided that you also include the original English version of this License and the original versions of those notices and disclaimers In case of a disagreement between the translation and the original version of this License or a notice or disclaimer the original version will prevail If a section in the Document is Entitled Acknowledgements Dedications or His tory the requirement section 4 to Preserve its Title section 1 will typically require changing the actual title TERMINATION You may not copy modify sublicense or distribute the Document except as expressly provided for under this License Any other attempt to copy modify sublicense or distribute the Document is void and will automatically terminate your rights under this License However parties who have received copies or rights from you under this License will not have their licenses terminated so long as such parties remain in full compliance FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation may publish new revised versions of the GNU Free Documentation License from time to time Such new versions will be similar in spirit to the
52. es it If k is not given restart prints the list and prompts for the integer index 2 error gt restart Choose an option by number 3 Specify a value to use instead of foo 2 Define foo to a given value 1 Return to read eval print level 1 3 Option number The simplest restart methods just perform their actions For example 2 error gt restart 1 Abort 1 gt Other methods will prompt for more input before continuing 2 error gt restart Choose an option by number 3 Specify a value to use instead of foo 2 Define foo to a given value 1 Return to read eval print level 1 d 3 3 Option number 3 Value to use instead of foo a b Value a b 1 gt 3 1 4 The Current REPL Environment Every REPL has a current environment which is the place where expressions are evaluated and definitions are stored When Scheme is started this environment is the value of the variable user initial environment There are a number of other environments in the 18 MIT GNU Scheme 9 0 system for example system global environment where the runtime system s bindings are stored You can get the current REPL environment by evaluating nearest repl environment There are several other ways to obtain environments For example if you have a proce dure object you can get a pointer to the environment in which it was closed by evaluating procedure environment procedure Here is the procedu
53. even if f2 is only called once Because of this the compiler has to allocate a memory cell to v How can the procedure return different results The fundamental reason is that the continuation may escape during the evaluation of compute 100 allowing the rest of the body of 2 to be executed again define keep define compute 100 call with current continuation lambda k set keep k 100 define p f2 p 100 keep 999 gt p re define v and p p gt 999 To avoid the inefficiency introduced to handle the general case the compiler must prove that the continuation cannot possibly escape The compiler knows that lambda expressions and constants do not let their continuations escape so order the internal definitions so that definitions of the following forms come first define x something define x lambda define f u v Note The IEEE Scheme standard permits only lambda expressions and constants as the value of internal defines Furthermore all internal definitions must appear before any other expressions in the body Following the standard simultaneously assures portability and avoids the implementation inefficiencies described in this section 4 3 2 Global variables Compiled code usually accesses variables in top level first class environments via variable caches Each compiled procedure has a set of variable caches for the global variables that it uses There are three kinds
54. execution history has recorded some information for this subproblem specifically a description of one reduction What follows is a description of the commands available in the debugger To understand how the debugger works you need to understand that the debugger has an implicit state that is examined and modified by commands The state consists of three pieces of information a subproblem a reduction and an environment frame Each of these parts of the implicit state is said to be selected thus one refers to the selected subproblem and so forth The debugger provides commands that examine the selected state and allow you to select different states Here are the debugger commands Each of these commands consists of a single letter which is to be typed by itself at the debugger prompt It is not necessary to type RET after these commands 40 MIT GNU Scheme 9 0 Traversing subproblems The debugger has several commands for traversing the structure of the contin uation It is useful to think of the continuation as a two dimensional structure a backbone consisting of subproblems and associated ribs consisting of reduc tions The bottom of the backbone is the most recent point in time that is where the debugger is positioned when it starts Each subproblem is numbered with 0 representing the most recent time point and ascending integers number ing older time points The u command moves up to older points in time and the d command moves
55. ferent It instead invokes the continuation that is waiting for the outer expression to finish In other words it is the same as invoking the j command in the next frame up So you can think of this as an abbreviation for the u command followed by the j command Wizard commands The m x and y commands are for Scheme wizards They are used to debug the MIT GNU Scheme implementation If you want to find out what they do read the source code Miscellaneous commands The i command will reprint the error message for the error that was in effect immediately before the debugger started The q command quits the debugger returning to the caller And the command prints a brief summary of the debugger s commands 5 3 Debugging Aids This section describes additional commands that are useful for debugging 42 MIT GNU Scheme 9 0 bkpt datum argument procedure Sets a breakpoint When the breakpoint is encountered datum and the arguments are typed just as for error and a read eval print loop is entered The environment of the read eval print loop is derived by examining the continuation of the call to bkpt if the call appears in a non tail recursive position the environment will be that of the call site To exit from the breakpoint and proceed with the interrupted process call the procedure continue Sample usage 1 gt begin write line foo bkpt test 2 test 3 write line bar gt done foo test 2 test 3
56. g garbage collection is dynamically allocated as needed Once the storage is allocated for the constant space and the heap Scheme will dynam ically adjust the proportion of the total that is used for constant space the stack and extra microcode storage is not included in this adjustment Previous versions of MIT GNU Scheme needed to be told the amount of constant space that was required when loading bands with the band option Dynamic adjustment of the heap and constant space avoids this problem Chapter 2 Running Scheme 7 If the size of the constant space is not specified it is automatically set to the correct size for the band being loaded it is rarely necessary to explicitly set the size of the constant space Additionally each band requires a small amount of heap space this amount is added to any specified heap size so that the specified heap size is the amount of free space available The Scheme expression print gc statistics shows how much heap and constant space is available see Section 3 4 Garbage Collection page 20 2 4 Command Line Options Scheme accepts the command line options detailed in the following sections The options may appear in any order with the restriction that the microcode options must appear before the runtime options and the runtime options must appear before any other arguments on the command line Any arguments other than these options will generate a warning message when Scheme starts
57. he GNU General Public License which is a copyleft license designed for free software We have designed this License in order to use it for manuals for free software because free software needs free documentation a free program should come with manuals providing the same freedoms that the software does But this License is not limited to software manuals it can be used for any textual work regardless of subject matter or whether it is published as a printed book We recommend this License principally for works whose purpose is instruction or reference APPLICABILITY AND DEFINITIONS This License applies to any manual or other work in any medium that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License Such a notice grants a world wide royalty free license unlimited in duration to use that work under the conditions stated herein The Document below refers to any such manual or work Any member of the public is a licensee and is addressed as you You accept the license if you copy modify or distribute the work in a way requiring permission under copyright law A Modified Version of the Document means any work containing the Document or a portion of it either copied verbatim or with modifications and or translated into another language A Secondary Section is a named appendix or a front matter section of the Document that deals exclusively with the rela
58. he library path DIRECTORY Directory where Edwin expects to find utility programs and documentation strings The default is edwin on the library path Filename of the shell program to use in shell buffers If not defined the SHELL environment variable is used instead Filename of the shell program to use in shell buffers and when executing shell commands Used to initialize the shell path name editor variable The default is bin sh on unix systems and cmd exe on Windows systems Used to initialize the exec path editor variable which is subsequently used for finding programs to be run as subprocesses 12 DISPLAY TERM LINES COLUMNS MIT GNU Scheme 9 0 Used when Edwin runs under unix and uses X11 Specifies the display on which Edwin will create windows Used when Edwin runs under unix on a terminal Terminal type Used when Edwin runs under unix on a terminal Number of text lines on the screen for systems that don t support TIOCGWINSZ Used when Edwin runs under unix on a terminal Number of text columns on the screen for systems that don t support TIOCGWINSZ 2 6 4 Environment Variables for Microsoft Windows These environment variables are specific to the Microsoft Windows implementation MITSCHEME_FONT MITSCHEME_ MITSCHEME_ MITSCHEME_ HOMEDRIVE HOMEPATH USERNAME USER USERDIR A string specifying a font name and characteristics for example Courier New 16
59. heme You may give run scheme a prefix argument in which case it will allow you to edit the command line that is used to invoke Scheme Do not remove the emacs option Note carefully In Emacs 19 and later the run scheme command exists but is different from the one described here In order to get this interface you must load the xscheme library before executing run scheme Scheme will be started up as a subprocess in a buffer called scheme This buffer will be in scheme interaction mode and all output from the Scheme process will go there The mode line for the scheme buffer will have this form scheme 1 Evaluator Scheme Interaction input The first field showing 1 in this example is the level number The second field showing Evaluator in this example describes the type of REPL that is running Other values include Debugger Where The mode after Scheme Interaction is one of input Scheme is waiting for input run Scheme is running an evaluation gc Scheme is garbage collecting When xscheme is loaded scheme mode is extended to include commands for evaluating expressions do C h m in any scheme mode buffer for the most up to date information M o Evaluates the current buffer xscheme send buf fer M z Evaluates the current definition xscheme send definition This is also bound to C M x C M z Evaluates the current region xschem
60. heme exits abnormally it tries to save any unsaved Edwin buffers The buffers are saved in an auto save file in case the original is more valuable than the unsaved version You can use the editor command M x recover file to recover the auto saved version The name used to specify an auto save file is operating system dependent under unix and on PC file systems with long file names foo scm will be saved as foo scm on PC file systems with short file names it will be saved as foo sav The following Scheme procedures are useful for recovering from bugs in Edwin s imple mentation All of them are designed for use when Edwin is not running they should not be used when Edwin is running These procedures are designed to help Edwin s implementors deal with bugs during the implementation of the editor they are not intended for casual use but as a means of recovering from bugs that would otherwise require reloading the editor s world image from the disk save editor files procedure Examines Edwin offering to save any unsaved buffers This is useful if some bug caused Edwin to die while there were unsaved buffers and you want to save the information without restarting the editor 56 MIT GNU Scheme 9 0 reset editor procedure Resets Edwin causing it to be reinitialized the next time that edit is called If you encounter a fatal bug in Edwin a good way to recover is to first call save editor files and then to call reset edi
61. ile remains after Scheme exits The time interval and the behavior are controlled by the following variables save uncompressed files variable This variable affects what happens when bci files are uncompressed It allows a trade off between performance and disk space There are three possible values 24 MIT GNU Scheme 9 0 f The uncompressed versions of bci files are never saved Each time the information is needed the bci file is uncompressed This option requires the minimum amount of disk space and is the slowest automatic Uncompressed versions of bci files are kept as temporary files The temporary files are deleted when Scheme exits or if they have not been used for a while This is the default t The bci files are uncompressed to permanent bif files These files remain on disk after Scheme exits and are rather large about twice the size of the corresponding bci files If you choose this option and you are running out of disk space you may delete the bif files They will be regenerated as needed uncompressed file lifetime variable The minimum length of time that a temporary uncompressed version of a bei file will stay on disk after it is last used The time is in milliseconds the default is 300000 five minutes load debugging info on demand variable If this variable is f then printing a compiled procedure will print the procedure s name
62. ints places where the program will pause for inspection Many bugs are detected when programs try to do something that is impossible like adding a number to a symbol or using a variable that does not exist this type of mistake is called an error Whenever an error occurs Scheme prints an error message and starts a new REPL For example using a nonexistent variable foo will cause Scheme to respond 1 gt foo Unbound variable foo To continue call RESTART with an option number RESTART 3 gt Specify a value to use instead of foo RESTART 2 gt Define foo toa given value RESTART 1 gt Return to read eval print level 1 2 error gt Sometimes a bug will never cause an error but will still cause the program to operate incorrectly For instance prime 7 f In this situation Scheme does not know that the program is misbehaving The program mer must notice the problem and if necessary start the debugging tools manually There are several approaches to finding bugs in a Scheme program e Inspect the original Scheme program e Use the debugging tools to follow your program s progress e Edit the program to insert checks and breakpoints Only experience can teach how to debug programs so be sure to experiment with all these approaches while doing your own debugging Planning ahead is the best way to ward off bugs but when bugs do appear be prepared to attack them with all the tools available 3
63. is complication is as follows the integrate operator declaration finds all the references to foo bar and replaces them with the lambda expression from the definition Then the integrate declarations take effect because the combination in which the reference to foo bar occurred supplies code that is substituted throughout the body of the procedure definition For example foo bar car baz cdr baz First use the integrate operator declaration lambda foo bar declare integrate foo bar vector ref vector ref foo bar 3 car baz cdr baz Next use the internal integrate declaration lambda foo bar vector ref vector ref car baz cdr baz 3 car baz cdr baz Next notice that the variables foo and bar are not used and eliminate them lambda vector ref vector ref car baz cdr baz 3 Finally remove the lambda to produce vector ref vector ref car baz cdr baz 3 Useful tip To see the effect of integration declarations and of macros on a source file pretty print the bin file like this be prepared for a lot of output sf foo scm pp fasload foo bin Chapter 4 Compiling Programs 27 4 2 3 Operator Replacement The replace operator declaration is provided to inform the compiler that certain oper ators may be replaced by other operators depending on the number of arguments For example Declaration declare replace operator map 2 map
64. lues are defined Gf This is the default Creates a window of some default size and uses that window as Edwin s main window Under unix if X11 is not available or if the DISPLAY environment variable is undefined Edwin will run on Scheme s console 52 MIT GNU Scheme 9 0 x Unix only Creates an X window and uses it as Edwin s main window This requires the DISPLAY environment variable to have been set to the appropriate value before Scheme was started x geometry Unix only Like x except that geometry specifies the window s ge ometry in the usual way Geometry must be a character string whose contents is an X geometry specification console Unix only Causes Edwin to run on Scheme s console or in unix termi nology the standard input and output If the console is not a terminal device or is not powerful enough to run Edwin an error will be signalled at initialization time win32 Windows only Creates a window and uses it as Edwin s main window 7 2 Leaving Edwin Once Edwin has been entered it can be exited in the following ways C x Zz Stop Edwin and return to Scheme suspend edwin The call to the procedure edit that entered Edwin returns normally A subsequent call to edit will resume Edwin where it was stopped C x c Offer to save any modified buffers then kill Edwin returning to Scheme save buffers kill edwin This is like the suspend edwin command except that a subsequent call to edit
65. means of environment variables See Section 2 6 Environment Variables page 10 e Icons Under Windows and with some window managers under X11 it is possible to create icons that invoke Scheme with different parameters 2 3 Memory Usage Some of the parameters that can be customized determine how much memory Scheme uses and how that memory is used This section describes how Scheme s memory is organized and used subsequent sections describe command line options and environment variables that you can use to customize this usage for your needs Scheme uses four kinds of memory e stack that is used for recursive procedure calls e A heap that is used for dynamically allocated objects like cons cells and strings Storage used for objects in the heap that become unreferenced is eventually reclaimed by garbage collection e constant space that is used for allocated objects like the heap Unlike the heap storage used for objects in constant space is not reclaimed by garbage collection Con stant space is used for objects that are essentially permanent like procedures in the runtime system e Some extra storage that is used by the microcode the part of the system that is implemented in C All kinds of memory except the last may be controlled either by command line options or by environment variables MIT GNU Scheme uses a two space copying garbage collector for reclaiming storage in the heap The second space used only durin
66. means to inspect this information For this reason the debugger is sometimes called a continuation browser Here is the transcript of a typical Scheme session showing a user evaluating the expres sion fib 10 Scheme responding with an unbound variable error for the variable fob and the user starting the debugger 1 gt fib 10 Unbound variable fob To continue call RESTART with an option number RESTART 3 gt Specify a value to use instead of fob RESTART 2 gt Define fob toa given value RESTART 1 gt Return to read eval print level 1 2 error gt debug There are 6 subproblems on the stack Subproblem level O this is the lowest subproblem level Expression from stack fob Environment created by the procedure FIB applied to 10 The execution history for this subproblem contains 1 reduction You are now in the debugger Type q to quit for commands 3 debug This tells us that the error occurred while trying to evaluate the expression fob while running fib 10 It also tells us this is subproblem level 0 the first of 6 subproblems that are available for us to examine The expression shown is marked from stack which tells us that this expression was reconstructed from the interpreter s internal data structures Another source of information is the execution history which keeps a record of expressions evaluated by the interpreter The debugger informs us that the
67. ning this is equivalent to evaluating cmdl interrupt abort previous C c C b C b Suspend whatever Scheme evaluation is running and start a breakpoint REPL The evaluation can be resumed by evaluating continue in that REPL at any time C c q Similar to typing exit at the REPL except that it works even if Scheme is running an evaluation and does not request confirmation C cz Similar to typing quit at the REPL except that it works even if Scheme is running an evaluation C c i Ignore the interrupt Type this if you made a mistake and didn t really mean to type C c C c Print help information This will describe any other options not documented here 3 1 3 Restarting Another way to exit a REPL is to use the restart procedure Chapter 3 Using Scheme 17 restart k procedure This procedure selects and invokes a restart method The list of restart methods is different for each REPL and for each error in the case of an error REPL this list is printed when the REPL is started Unbound variable foo To continue call RESTART with an option number RESTART 3 gt Specify a value to use instead of foo RESTART 2 gt Define foo toa given value RESTART 1 gt Return to read eval print level 1 2 error gt If the k argument is given it must be a positive integer index into the list in the example it must be between one and three inclusive The integer k selects an item from the list and invok
68. nment is specified and stt if environment is not specified apropos search package 47 user 4 package 48 O 4 list search negative 4 list search positive nt fs flag case sensitive search 44 re string search backward re string search forward re substring search backward re substring search forward search ordered subvector search ordered vector search protection list string search all string search backward string search forward substring search all substring search backward substring search forward vector binary search 5 4 Advising Procedures Giving advice to procedures is a powerful debugging technique MIT GNU Scheme 9 0 trace and break are useful examples of advice giving procedures Note that the advice system only works for interpreted procedures trace entry procedure Causes an informative message to be printed whenever procedure is entered The message is of the form Entering compound procedure 1 foo Args vall val2 sc procedure where vall val2 etc are the evaluated arguments supplied to the procedure trace entry fib fib 3 Entering compound procedure 19 fib Args 3 Entering compound procedure 19 fib Args 1 Entering compound procedure 19 fib Args 2 gt 3 trace exit procedure Causes an informative message to be printed when procedure terminates The mes sage contains the procedure its argument values and the value ret
69. ode for example begin do and let Scheme mode also provides support that is specific to Scheme programs much as Emacs Lisp mode does in Emacs Completion of global variable names is provided type the first few characters of a variable then type C M i and Edwin will attempt to complete the variable name using the current set of bound variables If C M i is given a prefix argument it will complete the name using the current set of interned symbols which includes the bound variables as a subset The M A command note the uppercase A will show the parameters of a procedure when point is inside a procedure call For example type the string quotient then press M A and the command will echo n d in the echo area With a prefix argument M A will insert the parameter names in the buffer at point so in this example the buffer would contain quotient n d after running C u M A 7 4 Evaluation Scheme mode also provides commands for evaluating Scheme expressions The simplest evaluation command is C x C e which evaluates the expression to the left of point This key is bound in all buffers even if they don t contain Scheme code The command M z evaluates the definition that point is in a definition is an expression starting with a left parenthesis in the leftmost column The command M prompts for an expression in the minibuffer evaluates it and prints the value in the echo area Other commands that evaluate larger amo
70. of variable cache read caches for getting the value of a variable referencing the variable write caches for changing the value and execute caches for calling the procedure assigned to that variable Sometimes the variable caches contain special objects called reference traps that in dicate that the operation cannot proceed normally and must either be completed by the system in order to keep the caches coherent or must signal an error For example the assignment set newline my better newline will cause the system to go to each compiled procedure that calls newline and update its execute cache to call the new procedure Obviously you want to avoid updating hundreds Chapter 4 Compiling Programs 33 of execute caches in a critical loop Using fluid let to temporarily redefine a procedure has the same inefficiency but twice To behave correctly in all situations each variable reference or assignment must check for the reference traps Sometimes you can prove that the variable a will always be bound b will never be unassigned and c there will never be any compiled calls to that variable The compiler can t prove this because it assumes that other independently compiled files might be loaded that invalidate these assumptions If you know that these conditions hold the following declarations can speed up and reduce the size of a program that uses global variables ignore reference traps variables declaration This de
71. on of the Document You may use the same title as a previous version if the original publisher of that version gives permission 62 N O MIT GNU Scheme 9 0 List on the Title Page as authors one or more persons or entities responsible for authorship of the modifications in the Modified Version together with at least five of the principal authors of the Document all of its principal authors if it has fewer than five unless they release you from this requirement State on the Title page the name of the publisher of the Modified Version as the publisher Preserve all the copyright notices of the Document Add an appropriate copyright notice for your modifications adjacent to the other copyright notices Include immediately after the copyright notices a license notice giving the public permission to use the Modified Version under the terms of this License in the form shown in the Addendum below Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document s license notice Include an unaltered copy of this License Preserve the section Entitled History Preserve its Title and add to it an item stating at least the title year new authors and publisher of the Modified Version as given on the Title Page If there is no section Entitled History in the Docu ment create one stating the title year authors and publisher of the Document as given on its
72. only if the debugging information for that procedure is already loaded Other wise it will force loading of the debugging information The default value is f sf filename destination procedure sf is the program that transforms a source code file into binary SCode form it is used on machines that do not support native code compilation It performs numerous optimizations that can make your programs run considerably faster than unoptimized interpreted code Also the binary files that it generates load very quickly compared to source code files The simplest way to use sf is just to say sf filename This will cause your file to be transformed and the resulting binary file to be written out with the same name but with pathname type bin If you do not specify a pathname type on the input file scm is assumed Like load the first argument to sf may be a list of filenames rather than a single filename sf takes an optional second argument which is the filename of the output file If this argument is a directory then the output file has its normal name but is put in that directory instead 4 2 Declarations Several declarations can be added to your programs to help cf and sf make them more efficient Chapter 4 Compiling Programs 25 4 2 1 Standard Names Normally all files have a line declare usual integrations near their beginning which tells the compiler that free variables whose names are defined in system glo
73. ontinuing the computation There are three commands that can be used to restart the computation that you are examining The first is the k command which shows the currently active restarts prompts you to select one and passes control to the it It is very similar to evaluating restart The other two commands allow you to invoke internal continuations This should not be done lightly invoking an internal continuation can violate as sumptions that the programmer made and cause unexpected results Each of these commands works in the same way it prompts you for an expression which is evaluated in the selected environment to produce a value The appropriate internal continuation is then invoked with that value as its sole argument The two commands differ only in which internal continuation is to be invoked The j command invokes the continuation associated with the selected subprob lem What this means is as follows when the description of a subproblem is printed it consists of two parts and expression and a subproblem being executed The latter is usually marked in the former by the specific character sequence The internal continuation of the subproblem is the code that is waiting for the subproblem being executed to return a value So in effect you are telling the program what the subproblem being executed will evaluate to and bypassing further execution of that code The z command is slightly dif
74. opying of the copies you make or distribute However you may accept compensation in exchange for copies If you distribute a large enough number of copies you must also follow the conditions in section 3 You may also lend copies under the same conditions stated above and you may publicly display copies 3 COPYING IN QUANTITY If you publish printed copies or copies in media that commonly have printed covers of the Document numbering more than 100 and the Document s license notice requires Cover Texts you must enclose the copies in covers that carry clearly and legibly all these Cover Texts Front Cover Texts on the front cover and Back Cover Texts on the back cover Both covers must also clearly and legibly identify you as the publisher of these copies The front cover must present the full title with all words of the title equally prominent and visible You may add other material on the covers in addition Copying with changes limited to the covers as long as they preserve the title of the Document and satisfy these conditions can be treated as verbatim copying in other respects If the required texts for either cover are too voluminous to fit legibly you should put the first ones listed as many as fit reasonably on the actual cover and continue the rest onto adjacent pages If you publish or distribute Opaque copies of the Document numbering more than 100 you must either include a machine readable Transparent copy along wi
75. or example of the correct order of the arguments to a procedure for all gt compiled procedure 40 boole x6 xC x20ECBO pa for all items predicate pp for all named lambda for all items predicate let loop items items 4 or null items 4 and predicate car items 4 loop cdr items where obj procedure The procedure where enters the environment examination system This allows en vironments and variable bindings to be examined and modified where accepts one letter commands The commands can be found by typing to the where gt prompt The optional argument obj is an object with an associated environment an environ ment a procedure or a promise If obj is omitted the environment examined is the read eval print environment from which where was called or an error or breakpoint environment if called from the debugger If a procedure is supplied where lets the user examine the closing environment of the procedure This is useful for debugging procedure arguments and values apropos string environment search parents procedure Search an environment for bound names containing string and print out the matching bound names If environment is specified it must be an environment or package name and it defaults to the current REPL environment The flag search parents specifies whether the environment s parents should be included in the search The default is f if enviro
76. ors are also always fixnums If you know that a value is always a small fixnum you can substitute the equivalent fixnum operation for the generic operation However care should be exercised if used improperly these operations can return incorrect answers or even malformed objects that confuse the garbage collector For a listing of all fixnum operations see Section Fixnum Operations in MIT GNU Scheme Reference Manual A fruitful area for inserting fixnum operations is in the index operations in tight loops 4 3 4 Flonum arithmetic Getting efficient flonum arithmetic is much more complicated and harder than getting effi cient fixnum arithmetic Flonum consing One of the main disadvantages of generic arithmetic is that not all kinds of number fit in a machine register Flonums have to be boxed because a 64 bit IEEE floating point number the representation that MIT GNU Scheme uses does not fit in a regular machine word This is true even on 64 bit architectures because some extra bits are needed to distinguish floating point numbers from other objects like pairs and strings Values are boxed by storing them in a small record in the heap Every floating point value that you see at the REPL is boxed Floating point values are unboxed only for short periods of time when they are in the machine s floating point unit and actual floating point operations are being performed Numerical calculations that happen to be using floating point numbe
77. ortcut to start up Edwin automatically put edit at the end of the command line 2 8 Leaving Scheme There are several ways that you can leave Scheme there are two Scheme procedures that you can call there are several Edwin commands that you can execute and there are graphical interface buttons and their associated keyboard accelerators that you can activate e Two Scheme procedures that you can call The first is to evaluate exit which will halt the Scheme system after first requesting confirmation Any information that was in the environment is lost so this should not be done lightly The second procedure suspends Scheme when this is done you may later restart where you left off Unfortunately this is not possible in all operating systems currently it works under unix versions that support job control i e all of the unix versions for which we distribute Scheme To suspend Scheme evaluate quit If your system supports suspension this will cause Scheme to stop and you will be returned to the shell Scheme remains stopped and can be continued using the job control commands of your shell If your system doesn t support suspension this pro cedure does nothing Calling the quit procedure is analogous to typing C z but it allows Scheme to respond by typing a prompt when it is unsuspended e Several Edwin commands that you can execute including save buffers kill scheme normally bound to C x C c and suspend scheme
78. placing them with calls to 4 You should provide a definition of as well although it is not required Chapter 4 Compiling Programs 29 Declaration declare reduce operator apply primitive cons group right wrapper global apply 1 Replacements apply f x y z w access apply f f cons x cons y cons z w apply f x y gt access apply 4f f cons x y apply f x apply f x apply f apply f apply apply reduce operator name declaration The general format of the declaration is brackets denote optional elements reduce operator name binop group ordering null value value null option singleton unop Grrapper wrap n maximum ail where e n and m are non negative integers e name is a symbol e binop value unop and wrap are simple expressions in one of these forms gt constant A constant variable A variable primitive primitive name arity The primitive procedure named primitive name The optional el ement arity specifies the number of arguments that the primitive accepts global var A global variable e null option is either always any one single none or empty e ordering is either left right or associative The meaning of these fields is e name is the name of the n ary operation to be reduced e binop is the binary operation into which the n ary operation is to be reduced 30 MIT GNU Scheme 9 0 e The group option
79. presentation and stick with it and it might not be easy to ascertain whether the advantages in one part of the program outweigh the disadvantages in another The flonum vector operations are flo vector cons n procedure Create a flonum vector of length n The contents of the vector are arbitrary and might not be valid floating point numbers The contents should not be used until initialized flo vector ref flonum vector index procedure flo vector set flonum vector index value procedure flo vector length flonum vector procedure These operations are analogous to the ordinary vector operations Examples The following operation causes no flonum consing because the flonum is loaded directly from the flonum vector into a floating point machine register added and stored again There is no need for a temporary boxed flonum flo vector set v O flo flo vector ref v 0 1 2 In this next example every time g is called a new boxed flonum has to be created so that a valid Scheme object can be returned If g is called more often than the elements of v are changed then an ordinary vector might be more efficient define g i flo vector ref v i Common pitfalls Pitfall 1 Make sure that your literals are floating point constants define f1 a flo a 1 define f2 a flo a 1 f1 will most likely cause a hardware error and certainly give the wrong answer f2 is correct 36 MIT GNU Scheme 9 0 Pitfall 2 I
80. programs and use the editor The release notes are included as an appendix This document discusses many operating system specific features of the MIT GNU Scheme implementation In order to simplify the discussion we use abbreviations to re fer to some operating systems When the text uses the term unix this means any of the unix systems that we support including GNU Linux and the BSD variants We use the term Windows to collectively refer to the modern Microsoft Windows 32 bit operating sys tems Windows NT Windows 2000 and Windows XP We use the term PC to refer to any computer running Windows Thus we consider a PC to be a system with a DOS like file system using backslashes for directory separators drive letters CR LF line termination and potentially the hideous 8 3 short filenames The primary distribution site for this software is http www gnu org mit scheme Although our software is distributed from other sites and in other media the complete distribution and the most recent release is always available at our site To report bugs use the bug reporting tool at http savannah gnu org projects mit scheme Please include the output of the identify world procedure see Section 2 1 Basics of Starting Scheme page 5 so we know what version of the system you are using Chapter 1 Installation 3 1 Installation This chapter describes how to install MIT GNU Scheme The release is supported under various unix and Windows
81. px EEG ENO E pF ERE 45 Urace entry EE enge 44 EE eeneg 44 MIT GNU Scheme 9 0 U unadviSe ida e ehe Ed UR CR SERE RACE E 47 unadvise entry EE 47 ET GE EE 47 tele TEE 46 unbreak entry e epe RET RII FR een 46 unbre ak exit l2iogecemerd4 ees e perunt 46 Hd Of asus Fo Ate WS uel Ie PA LM Pad pie 33 dek ra ENEE 45 untrace entry i EE 45 untrace exit EE 45 user initial environment 17 usual integrations ccc eee eee eee 25 xscheme select process buffer 49 xscheme send breakpoint interrupt 50 xscheme send buffer eese 49 xscheme send control g interrupt 50 xscheme send control u interrupt 50 xscheme send control x interrupt 50 xscheme send definition 49 xscheme send previous expression 49 Zscheme send proceed 50 xscheme send region 0 cece eee 49 xscheme yank previous send 49 Appendix F Concept Index Appendix F Concept Index e EEN 7 20 Let EE 16 breakpolinis 1 i iaccdaaiiee tee REENEN 37 browser Continuation 0 0e eee 38 e EE 37 bugs reporting 1 EE 16 e 16 EE cse 16 CHO CHD EE 16 50 CHC CFC EEN 16 50 CHO C pius e dadaache EE 50 GH EE 49 CAC Dat et EERSTEN tes 16 50 CHC CHR EE 16 50 GAO CRY EE 49 e DEE 16 CRO EE 16 Ee EE e 16 pu E 16 CAM os E EET 49 M iens arta de nU ens dat bug dent 16 poc rp 16 c A Lm 52
82. re that changes the REPL s environment ge environment procedure Changes the current REPL environment to be environment ge stands for Goto Environment Environment is allowed to be a procedure as well as an environment object If it is a procedure then the closing environment of that procedure is used in its place pe procedure This procedure is useful for finding out which environment you are in pe stands for Print Environment If the current REPL environment belongs to a package then pe returns the package name a list of symbols If the current REPL environment does not belong to a package then the environment is returned 3 2 Loading Files To load files of Scheme code use the procedure load load filename environment syntax table purify procedure Filename may be a string naming a file or a list of strings naming multiple files Environment if given is the environment to evaluate the file in if not given the current REPL environment is used Syntax table is no longer used and if supplied will be ignored The optional argument purify is a boolean that says whether to move the contents of the file into constant space after it is loaded but before it is evaluated This is performed by calling the procedure purify see Section 3 4 Garbage Collection page 20 If purify is given and true this is done otherwise it is not load determines whether the file to be loaded is binary or source code and perfo
83. riable specification These expressions name sets of variables all is the set of all variables none is the empty set free is all of the variables bound outside the current block bound is all of the variables bound in the current block and assigned is all of the variables for which there exists an assignment i e set union setl set variable specification intersection set set2 variable specification difference setl set2 variable specification For example to ignore reference traps on all the variables except x y and any variable that is assigned to 34 MIT GNU Scheme 9 0 declare ignore reference traps difference all union assigned set x y 4 3 3 Fixnum arithmetic The usual arithmetic operations like and are called generic arithmetic operations because they work for all appropriate kinds of number A fixnum is an exact integer that is small enough to fit in a machine word In MIT GNU Scheme fixnums are 26 bits on 32 bit machines and 58 bits on 64 bit machines it is reasonable to assume that fixnums are at least 24 bits Fixnums are signed they are encoded using 2 s complement All exact integers that are small enough to be encoded as fixnums are always encoded as fixnums in other words any exact integer that is not a fixnum is too big to be encoded as such For this reason small constants such as O or 1 are guaranteed to be fixnums In addition the lengths of and valid indexes into strings and vect
84. rms the appropriate action By convention files of source code have a pathname type of scm and files of binary SCode have pathname type bin Native code bina ries have pathname type com See the description of pathname type in Section Components of Pathnames in MIT GNU Scheme Reference Manual load noisily variable If load noisily is set to t load will print the value of each expression in the file as it is evaluated Otherwise nothing is printed except for the value of the last expression in the file Note the noisy loading feature is implemented for source code files only Chapter 3 Using Scheme 19 All pathnames are interpreted relative to a working directory which is initialized when Scheme is started The working directory can be obtained by calling the procedure pwd or modified by calling the procedure cd see Section Working Directory in MIT GNU Scheme Reference Manual Files may be loaded when Scheme first starts see the load command line option for details load option symbol no error procedure Loads the option specified by symbol if already loaded does nothing Returns sym bol if there is no such option an error is signalled However if no error is specified and true no error is signalled in this case and f is returned A number of built in options are defined compress Support to compress and uncompress files Undocumented see the source file runtime cpress scm Used by
85. rs cause many tem porary floating point numbers to be allocated It is not uncommon for numerical programs to spend over half of their time creating and garbage collecting the boxed flonums Consider the following procedure for computing the distance of a point x y from the origin define distance x y sqrt C x x C y y The call distance 0 3 0 4 returns a new boxed flonum 0 5 The calculation also generates three intermediate boxed flonums This next version works only for flonum inputs generates only one boxed flonum the result and runs eight times faster Chapter 4 Compiling Programs 35 define flo distance x y flo sqrt flo flo x x flo y y Note that flo operations are usually effective only within a single arithmetic expression If the expression contains conditionals or calls to procedures then the values tend to get boxed anyway Flonum vectors Flonum vectors are vectors that contain only floating point values in much the same way as a string is a vector containing only character values Flonum vectors have the advantages of compact storage about half that of a conventional vector of flonums and judicious use of flonum vectors can decrease flonum consing The disadvantages are that flonum vectors are incompatible with ordinary vectors and if not used carefully can increase flonum consing Flonum vectors are a pain to use because they require you to make a decision about the re
86. s the first line Each line beginning with S represents either a subproblem or stack frame A subproblem line may be followed by one or more indented lines beginning with the letter R which represent reductions associated with that subproblem The subproblems are indexed with the natural numbers To obtain a more complete description of a subproblem or reduction click the mouse on the desired line or move the cursor to the line using the arrow keys or C n and C p The description buffer will display the additional information The description buffer contains three major regions The first region contains a pretty printed version of the current expression The current subproblem within the expression is Chapter 7 Edwin 55 highlighted The second region contains a representation of the frames of the environment of the current expression The bindings of each frame are listed below the frame header If there are no bindings in the frame none will be listed The frame of the current expression is preceded with gt The bottom of the description buffer contains a third region for evaluating expressions in the environment of the selected subproblem or reduction This is the only portion of the buffer where editing is possible This region can be used to find the values of variables in different environments or even to modify variable values or data structures note that variables in compiled code cannot usually be modified
87. t To do this add their titles to the list of Invariant Sections in the Modified Version s license notice These titles must be distinct from any other section titles Appendix B GNU Free Documentation License 63 You may add a section Entitled Endorsements provided it contains nothing but endorsements of your Modified Version by various parties for example statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard You may add a passage of up to five words as a Front Cover Text and a passage of up to 25 words as a Back Cover Text to the end of the list of Cover Texts in the Modified Version Only one passage of Front Cover Text and one of Back Cover Text may be added by or through arrangements made by any one entity If the Document already includes a cover text for the same cover previously added by you or by arrangement made by the same entity you are acting on behalf of you may not add another but you may replace the old one on explicit permission from the previous publisher that added the old one The author s and publisher s of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version 5 COMBINING DOCUMENTS You may combine the Document with other documents released under this License under the terms defined in section 4 above for modified versions provided that
88. t is tempting to insert calls to exact gt inexact to coerce values into flonums This does not always work because complex numbers may be exact or inexact too Also the current implementation of exact gt inexact is slow Pitfall 3 A great deal of care has to be taken with the standard math procedures For example when called with a flonum both sqrt and asin can return a complex number e g with argument 1 5 Chapter 5 Debugging 37 5 Debugging Parts of this chapter are adapted from Don t Panic A 6 001 User s Guide to the Chipmunk System by Arthur A Gleckler Even computer software that has been carefully planned and well written may not always work correctly Mysterious creatures called bugs may creep in and wreak havoc leaving the programmer to clean up the mess Some have theorized that a program fails only because its author made a mistake but experienced computer programmers know that bugs are always to blame This is why the task of fixing broken computer software is called debugging It is impossible to prove the correctness of any non trivial program hence the Cynic s First Law of Debugging Programs don t become more reliable as they are debugged the bugs just get harder to find Scheme is equipped with a variety of special software for finding and removing bugs The debugging tools include facilities for tracing a program s use of specified procedures for examining Scheme environments and for setting breakpo
89. take the amount of free storage divide by 1000 and add this figure to the current value used for the heap command line option Unfortunately there is no way to adjust the heap size without restarting Scheme toggle gc notification procedure Toggles GC notification on and off If GC notification is turned on turns it off otherwise turns it on Chapter 4 Compiling Programs 23 4 Compiling Programs Note the procedures described in this section are only available when the compiler command line option is specified 4 1 Compilation Procedures cf filename destination procedure This is the program that transforms a source code file into native code binary form If destination is not given as in cf foo cf compiles the file foo scm producing the file foo com incidentally it will also produce foo bin foo bci and possibly foo ext If you later evaluate load foo foo com will be loaded rather than foo scm If destination is given it says where the output files should go If this argument is a directory they go in that directory e g cf foo bar will take foo scm and generate the file bar foo com If destination is not a directory it is the root name of the output cf foo bar takes foo scm and generates bar com 6 About the bci files these files contain the debugging information that Scheme uses
90. ted garbage that has accumulated since then The only accurate way to determine the size of live storage is to subtract the value of gc flip from the size of the heap The size of the heap can be determined by adding the in use and free figures reported by print gc statistics 22 MIT GNU Scheme 9 0 print gc statistics constant in use 534121 words 521 blocks 617 words constant free 128 words O blocks 128 words heap in use 34845 words 34 blocks 29 words heap free 205530 words 200 blocks 730 words GC 1 took 0 13 81 CPU time 0 15 1 real time free 207210 No value set gc notification Jon procedure Controls whether the user is notified of garbage collections If on is true notification is enabled otherwise notification is disabled If on is not given it defaults to t When Scheme starts notification is disabled The notification appears as a single line like the following showing how many garbage collections have occurred the time taken to perform the garbage collection and the free storage remaining in words after collection GC 5 took 0 50 8 CPU time 0 70 2 real time free 364346 To operate comfortably the amount of free storage after garbage collection should be a substantial proportion of the heap size If the CPU time percentage is consistently high over 20 you should consider running with a larger heap A rough rule of thumb to halve the GC overhead is to
91. th each Opaque copy or state in or with each Opaque copy a computer network location from which the general network using public has access to download using public standard network protocols a complete Transparent copy of the Document free of added material If you use the latter option you must take reasonably prudent steps when you begin distribution of Opaque copies in quantity to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy directly or through your agents or retailers of that edition to the public It is requested but not required that you contact the authors of the Document well before redistributing any large number of copies to give them a chance to provide you with an updated version of the Document 4 MODIFICATIONS You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above provided that you release the Modified Version under precisely this License with the Modified Version filling the role of the Document thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it In addition you must do these things in the Modified Version A Use in the Title Page and on the covers if any a title distinct from that of the Document and from those of previous versions which should if there were any be listed in the History secti
92. ther things with the editor A REPL buffer captures all printed output from an evaluated expression as well as supporting interactive programs such as debug 54 MIT GNU Scheme 9 0 For these and other reasons REPL buffers are the preferred means for interacting with the Scheme interpreter When Edwin starts it has one buffer a REPL buffer called scheme The command M x rep selects this buffer if it exists otherwise it creates a new REPL buffer If you want two REPL buffers just rename the scheme buffer to something else and run M x rep1 again REPL buffers support all the same evaluation commands that Scheme mode does in fact REPL buffers use a special mode called REPL mode that inherits from Scheme mode Thus any key bindings defined in Scheme mode are also defined in REPL mode One exception to this is the M o command which is deliberately undefined in REPL mode otherwise it would be too easy to re evaluate all the previously evaluated expressions in the REPL buffer In addition to evaluation commands REPL mode provides a handful of special commands for controlling the REPL itself The commands C c C x and C c C u abort the current evaluation returning to the current or previous REPL levels respectively The command C c C b interrupts the current evaluation entering a breakpoint Each REPL buffer maintains a history of the expressions that were typed into it Sev eral commands allow you to access the contents of
93. tionship of the publishers or authors of the Document to the Document s overall subject or to related matters and contains nothing that could fall directly within that overall subject Thus if the Document is in part a textbook of mathematics a Secondary Section may not explain any mathematics The relationship could be a matter of historical connection with the subject or with related matters or of legal commercial philosophical ethical or political position regarding them The Invariant Sections are certain Secondary Sections whose titles are designated as being those of Invariant Sections in the notice that says that the Document is released 60 MIT GNU Scheme 9 0 under this License If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant The Document may contain zero Invariant Sections If the Document does not identify any Invariant Sections then there are none The Cover Texts are certain short passages of text that are listed as Front Cover Texts or Back Cover Texts in the notice that says that the Document is released under this License A Front Cover Text may be at most 5 words and a Back Cover Text may be at most 25 words A Transparent copy of the Document means a machine readable copy represented in a format whose specification is available to the general public that is suitable for revising the document straightforwardly with generic text
94. tle Page means the text near the most prominent appearance of the work s title preceding the beginning of the body of the text A section Entitled XYZ means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language Here XYZ stands for a specific section name mentioned below such as Acknowledgements Dedications Endorsements or History To Preserve the Title of such a section when you modify the Document means that it remains a section Entitled XYZ according to this definition The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document These Warranty Disclaimers are considered to be included by reference in this License but only as regards disclaiming warranties any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License VERBATIM COPYING You may copy and distribute the Document in any medium either commercially or noncommercially provided that this License the copyright notices and the license notice saying this License applies to the Document are reproduced in all copies and Appendix B GNU Free Documentation License 61 that you add no other conditions whatsoever to those of this License You may not use technical measures to obstruct or control the reading or further c
95. to find out what is in error is to do some poking around in the error REPL If you abort out of it the context of the error will be destroyed and you may not be able to find out what happened 16 MIT GNU Scheme 9 0 3 1 2 Interrupting Scheme has several interrupt keys which vary depending on the underlying operating sys tem under unix C g and C c under Windows C g C b C x and C u The C g key stops any Scheme evaluation that is running and returns you to the top level REPL C c prompts you for another character and performs some action based on that character It is not necessary to type RET after C g or C c nor is it needed after the character that C c will ask you for Here are the definitions of the more common interrupt keys on unix type C c for more possibilities Note that in any given implementation only a subset of the following keys is available C c C c C g Abort whatever Scheme evaluation is currently running and return to the top level REPL If no evaluation is running this is equivalent to evaluating cmdl interrupt abort top level C c C x C x Abort whatever Scheme evaluation is currently running and return to the cur rent REPL If no evaluation is running this is equivalent to evaluating cmdl interrupt abort nearest C c C u C u Abort whatever Scheme evaluation is running and go up one level If you are already at level number 1 the evaluation is aborted leaving you at level 1 If no evaluation is run
96. to write scripts that invoke Scheme with your favorite command line options For example you might not have enough memory to run Edwin or the compiler with its default memory parameters it will print something like Not enough memory for this configuration and halt when started so you can write a shell script unix or bat file Windows that will invoke Scheme with the appropriate heap and other parameters e Scheme supports init files an init file is a file containing Scheme code that is loaded when Scheme is started immediately after the identification banner and before the in 6 MIT GNU Scheme 9 0 put prompt is printed This file is stored in your home directory which is normally spec ified by the HOME environment variable Under unix the file is called scheme init on the PC it is called scheme ini In addition when Edwin starts up it loads a separate init file from your home directory into the Edwin environment This file is called edwin under unix and edwin ini on the PC see Section 7 1 Starting Edwin page 51 You can use both of these files to define new procedures or commands or to change defaults in the system The no init file command line option causes Scheme to ignore the Scheme init file see Section 2 4 Command Line Options page 7 e Environment variables Most microcode parameters and some runtime system and Edwin parameters can be specified by
97. tor That should completely reset the editor to its initial state reset editor windows procedure Resets Edwin s display structures without affecting any of the buffers or their con tents This is useful if a bug in the display code causes Edwin s internal display data structures to get into an inconsistent state that prevents Edwin from running Appendix A Release Notes 57 Appendix A Release Notes The release notes are online at http www gnu org software mit scheme release html Appendix B GNU Free Documentation License 59 Appendix B GNU Free Documentation License Version 1 2 November 2002 Copyright 2000 2001 2002 Free Software Foundation Inc 51 Franklin St Fifth Floor Boston MA 02110 1301 USA Everyone is permitted to copy and distribute verbatim copies of this license document but changing it is not allowed 0 PREAMBLE The purpose of this License is to make a manual textbook or other functional and useful document free in the sense of freedom to assure everyone the effective freedom to copy and redistribute it with or without modifying it either commercially or non commercially Secondarily this License preserves for the author and publisher a way to get credit for their work while not being considered responsible for modifications made by others This License is a kind of copyleft which means that derivative works of the document must themselves be free in the same sense It complements t
98. unts of code are C M z which evaluates all of the expressions in the region and M o which evaluates the entire buffer Both of these commands are potentially dangerous in that they will evaluate anything that appears to be an expression even if it isn t intended to be Normally these commands evaluate expressions by sending them to a REPL buffer which performs the evaluations in a separate thread This has two advantages it allows you to continue editing while the evaluation is happening and it keeps a record of each evaluation and its printed output If you wish to stop a running evaluation and to erase any pending expressions use the C c C c command from any Scheme buffer Note that by default Edwin starts up with one REPL buffer called scheme If you would prefer to have Scheme mode evaluation commands evaluate directly rather than sending expressions to the REPL buffer set the Edwin variable evaluate in inferior repl to f In this case you will not be able to use Edwin while evaluation is occurring any output from the evaluation will be shown in a pop up buffer when the evaluation finishes and you abort the evaluation using C g 7 5 REPL Mode Edwin provides a special mechanism for interacting with Scheme read eval print loops REPL buffers A REPL buffer is associated with a Scheme REPL running in a separate thread of execution because of this expressions may be evaluated in this buffer while you simultaneously do o
99. ure Returns the advice procedures if any that are attached to procedure This is returned as a list of two lists the first list is all of the entry advice procedures attached to procedure and the second is all of the exit advice procedures unadvise entry procedure procedure Removes all entry advice procedures from procedure If procedure is not given the default is all entry advised procedures unadvise exit procedure procedure Removes exit advice procedures from procedure If procedure is not given the default is all exit advised procedures unadvise procedure procedure Removes all advice procedures from procedure This is a combination of unadvise entry and unadvise exit If procedure is not given the default is all advised pro cedures Chapter 6 GNU Emacs Interface 49 6 GNU Emacs Interface There is an interface library called xscheme distributed with MIT GNU Scheme and GNU Emacs which facilitates running Scheme as a subprocess of Emacs If you are using a recent version of GNU Emacs say version 22 or later use the xscheme file that comes with it Otherwise use the one that is in the Scheme distribution This interface works under unix only because it requires unix signals for its operation Porting it to Windows would require reimplementing the interface to eliminate the use of signals We have no plans to do this To invoke Scheme from Emacs load the xscheme library then use M x run sc
100. urned by the procedure trace exit fib fib 3 1 lt compound procedure 19 fib procedure Chapter 5 Debugging 45 4 Args 1 41 D 4 lt compound procedure 19 fib 4 Args 2 4 3 4 lt compound procedure 19 fib 4 Args 3 gt 3 trace both procedure procedure trace procedure procedure Equivalent to calling both trace entry and trace exit on procedure trace is the same as trace both trace both fib fib 3 4 Entering compound procedure 19 fib 4 Args 3 4 Entering compound procedure 19 fib 4 Args 1 7 4 lt compound procedure 19 fib R Args 1 4 Entering compound procedure 19 fib 4 Args 2 4 2 4 lt compound procedure 19 fib 4 Args 2 4 3 lt compound procedure 19 fib 4 Args 3 gt 3 untrace entry procedure procedure Stops tracing the entry of procedure If procedure is not given the default is to stop tracing the entry of all entry traced procedures untrace exit procedure procedure Stops tracing the exit of procedure If procedure is not given the default is all exit traced procedures untrace procedure procedure Stops tracing both the entry to and the exit from procedure If procedure is not given the default is all traced procedures break entry procedure procedure Like trace entry with the additional effect that a breakpoint is entered when pro cedure is invoked Both procedure and its argum
101. ves object from the heap into constant space Has no effect if object is already stored in constant space Object is moved in its entirety if it is a compound object such as a list a vector or a record then all of the objects that object points to are also moved to constant space There are three important effects associated with moving an object to constant space The first and most important effect is that the object takes up half as much space because when in the heap the system must reserve space for the object in both the active heap and the inactive heap if the object is in constant space it is not copied and therefore no extra space is required The second effect is that garbage collection will take less time because object will no longer be copied The third effect is that the space allocated to object is permanently allocated because constant space is never cleaned any unreachable objects in constant space remain there until the Scheme process is terminated The optional argument pure space is obsolete it defaults to t and when explicitly specified should always be t The optional argument queue if specifies that object should be moved to con stant space immediately otherwise object is queued to be moved during the next garbage collection This argument defaults to t The reason for queuing these re quests is that moving an object to constant space requires a garbage collection to occur a relatively slow process B
102. vided by filename filename should not specify a file type and the source code file that it names must have been previously processed by the compiler If filename is a relative filename the normal case it is interpreted as being relative to the file in which the declaration appears Thus if the declaration appears in file usr cph foo scm then the compiler looks for a file called usr cph filename ext Note When the compiler finds top level integrations it collects them and out puts them into an auxiliary file with extension ext This ext file is what the integrate external declaration refers to Note that the most common use of this facility in line coding of procedure definitions requires a somewhat complicated use of these declarations Because this is so common there 26 MIT GNU Scheme 9 0 is a special form define integrable which is like define but performs the appropriate declarations For example define integrable foo bar foo bar vector ref vector ref foo bar 3 Here is how you do the same thing without this special form there should be an integrate operator declaration for the procedure s name and internal to the proce dure s definition an integrate declaration for each of the procedure s parameters like this declare integrate operator foo bar define foo bar lambda foo bar declare integrate foo bar vector ref vector ref foo bar 3 The reason for th
103. with the Invariant Sections being list their titles with the Front Cover Texts being list and with the Back Cover Texts being list If you have Invariant Sections without Cover Texts or some other combination of the three merge those two alternatives to suit the situation If your document contains nontrivial examples of program code we recommend releasing these examples in parallel under your choice of free software license such as the GNU General Public License to permit their use in free software Appendix C Environment variable Index Appendix C Environment variable Index COLUMNS esssRes tends on Rer S n RR d ends 12 DISPLAY eere ete euh edd een 12 EDNIN BINARY DIRECTORY ti EDWIN_ETC_DIRECTORY 0 ERI Ena 11 EDWIN_INFO_DIRECTORY 00 tI H IO EE 11 IN IEN 11 HOMEDRIVE 2m ROLE NDCHES RI PIU ES 11 12 HOMEPA TH EE 11 12 LINES EE 12 MITSCHEME_BACKGROUND unnnnnnnnnnnnnnnn 12 MITSCHEME BAND 000s cee ne nne i5 40 MITSCHEME CONSTANT sees 10 67 MITSGOHEME FONT meme Rex tede 12 MITSCHEME FOREGROUND sese I2 MITSCHEME GEOMETRY 0 0 cee ee ee eee 12 MITSGHEME HEAP see erh reete 10 MITSCHEME NF DIRECTURN 11 MITSCHEME_LIBRARY_PATH 8 10 MITSCHEME_LOAD_OPTIONS 000 11 METSCHEME STACK 2 EE ee Seege 10 PATH DEE T SHEL cei eee ES RESR ARDENTEM REP ae 11 RRE 11 TERM EE T2 RN 11 TMPDIR EE D USER EE 12 US
104. y queuing the requests this overhead is avoided because moving an object during a garbage collection has no effect on the time of the garbage collection Furthermore if several requests are queued they can all be processed together in one garbage collection while if done separately they would each require their own garbage collection flush purification queue procedure Forces any pending queued purification requests to be processed This examines the purify queue and if it contains any requests forces a garbage collection to process them If the queue is empty does nothing print gc statistics procedure Prints out information about memory allocation and the garbage collector The information is printed to the current output port Shows how much space is in use and how much is free separately for the heap and constant space The amounts are shown in words and also in 1024 word blocks the block figures make it convenient to use these numbers to adjust the arguments given to the heap and constant command line options Following the allocation figures information about the most recent 8 garbage collections is shown in the same format as a GC notification Note that these numbers are accurate at the time that print gc statistics is called In the case of the heap the in use figure shows how much memory has been used since the last garbage collection and includes all live objects as well as any uncollec

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