Home

MIT Scheme User's Manual: MIT Scheme User's Manual

1. 1 2 Windows Installation This section describes how to install MIT Scheme on Windows 95 Windows 98 Windows Me Windows NT 4 0 Windows 2000 or Windows XP The software should also work on older versions of Windows NT but we haven t tested it there MIT Scheme is distributed as a self installing executable Installation of the software is straightforward Simply execute the downloaded file and answer the installer s questions The installer will allow you to choose the directory in which MIT 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 Scheme 7 7 lt gt L lt lt Up gt gt Top Contents Index _ 1 3 OS 2 Installation This section describes how to install MIT Scheme on a machine running OS 2 2 1 or later This release of MIT Scheme has been tested only on OS 2 Warp 4 0 It was compiled using IBM Visual Age C version 3 0 and the OS 2 Toolkit version 4 0 1 3 1 OS 2 Installation Procedure 1 3 2 Environment Variables lt gt L lt lt Up gt gt Top Contents Index _ 1 3 1 OS 2 Installation Procedure After unpacking the ZIP file os2 zip you will have these directories containing the following files exe The executable programs scheme exe and bchschem exe dll The dynamic
2. 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 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 i f expression can be reduced to the problem cons prime n once we know that prime n istrue 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 define factorial n if lt n 2 bh
3. 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 isat subproblem level 1 and n factorial n 1 isatsubproblem level 2 These expressions 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 lt gt Lee Le gt gt Top Contents Index _ 5 2 The Command Line Debugger There are two debuggers available with MIT Scheme One of them runs under Edwin and is described in that section of this document see section 7 6 The Edwin Debugger 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 caused the error the debugger provides you with the means
4. the constant t Restart exactly where you were when the call to disk save was performed This is especially useful for saving your state when an error has occurred and you are not in the top level REPL the constant f Just like t 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 lt gt L lt lt Up gt Top Contents Index _ 3 4 Garbage Collection This section describes procedures that control garbage collection See section 2 3 Memory Usage for a discussion of how MIT Scheme uses memory procedure ge flip safety margin 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 you should not specify safety margin unless you
5. 3 State on the Title page the name of the publisher of the Modified Version as the 10 11 12 13 14 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 and 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 Document create one stating the title year authors and publisher of the Document as given on its 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 b
6. MITSCHEME__GC_WINDOW_SIZE default 16 The size in blocks of windows into new space in the GC file Overridden by gc window size The following environment variables are only used by an experimental version of Bchscheme that uses unix System V style shared memory and then only if the gcdrone program is installed MITSCHEME_GC_DRONE default gcdrone The program to use as the I O drone during garbage collection Overridden by gc drone MITSCHEME__GC_READ_OVERLAP default 0 The maximum number of simultaneous read operations Overridden by gc read overlap MITSCHEME_GC_WRITE_OVERLAP default 0 The maximum number of simultaneous write operations Overridden by gc write overlap gt ss lt gt L lt lt J Up gt gt Top Contents Index _ 2 6 3 Environment Variables for the Runtime System These environment variables are referred to by the runtime system HOME Directory in which to look for init files E g c users joe or home joe This variable needs to be set on OS 2 and Windows 9x Under Windows NT 2000 XP the environment variables HOMEDRIVE and HOMEPATH set by the operating system are used instead Under unix HOME is set by the login shell TMPDIR TEMP TMP 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 tm
7. gt gt Top Contents Index _ 2 6 1 Environment Variables for the Microcode 2 4 Command Line Options 2 6 1 Environment Variables for the Microcode FGHILMNOPQRS This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt L lt lt UpI gt gt Top Contents Index _ Index N X Jump to E a ABCDE TUVWX Index Entry nearest repl environment None OS 2 pathname type PC pe PP print ge statistics print g r statistics procedure environment FGHILMNOPQRS Section 3 1 4 The Current REPL Environment 4 3 2 Global variables Introduction 5 3 Debugging Aids 2 6 4 Environment Variables for Edwin 3 2 Loading Files Introduction 3 1 4 The Current REPL Environment 5 3 Debugging Aids 2 4 Command Line Options 3 4 Garbage Collection 3 1 4 The Current REPL Environment procedures finding prompt REPL purify purify pwd reduce operator reduce operator reduction reference traps release number REPL REPL restarting from replace operator reporting bugs reset editor reset editor windows restart run scheme 5 3 Debugging Aids 3 1 1 The Prompt and Level Number 3 2 Loading Files 3 4 Garbage Collection 3 2 Loading Files 2 8 Leaving Scheme 3 1 2 Interrupting 4 2 4 Operator Reduction 4 2 4 Operator Reduction 5 1 Subproblems and Reductions
8. s lt Up 2 gt Top Contents Index 2 3 1 3 Restarting Another way to exit a REPL is to use the restart procedure procedure restart k 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 to a 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 invokes 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 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
9. 15 host 15 type index 0 name procedure pa procedure pa prints the arguments of procedure This can be used to remind yourself for 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 5 or null items and predicate car items 2 loop cdr items procedure where obj The procedure where enters the environment examination system This allows environments 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 environment 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 procedure apropos string environment search parents Search an environment for bound names containing string and print out the matching bound names If
10. unbreak exit 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 procedure proc Returns the procedure in which the breakpoint has stopped procedure args Returns the arguments to the procedure in which the breakpoint has stopped The arguments are returned as a newly allocated list procedure result 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 procedure 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 ad
11. unix cmd exe PC Filename of the shell program to use in shell buffers and when executing shell commands Used to initialize the she 1 1 path name editor variable PATH Used to initialize the exec path editor variable which is subsequently used for finding programs to be run as subprocesses DISPLAY Used when Edwin runs under unix and uses X11 Specifies the display on which Edwin will create windows TERM Used when Edwin runs under unix on a terminal Terminal type LINES default auto sense Used when Edwin runs under unix on a terminal Number of text lines on the screen for systems that don t support TIOCGWINSZ COLUMNS default auto sense Used when Edwin runs under unix on a terminal Number of text columns on the screen for systems that don t support TIOCGWINSZ lt gt L lt lt Up gt Top Contents Index 2 6 5 Environment Variables for Microsoft Windows These environment variables are specific to the Microsoft Windows implementation MITSCHEME_FONT default determined by operating system A string specifying a font name and characteristics for example Courier New 16 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
12. 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 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 lt gt lt lt LUp gt gt Top Contents Index 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 th
13. 1 Option number 3 Value to use instead of foo a b Value a b 1 gt lt gt L lt lt Up gt Top Contents Index _ 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 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 procedure object you can get a pointer to the environment in which it was closed by evaluating procedure environment procedure Here is the procedure that changes the REPL s environment procedure ge environment 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 procedure pe 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 envir
14. 4 3 2 Global variables 2 1 Basics of Starting Scheme 3 1 The Read Eval Print Loop 3 1 3 Restarting 4 2 3 Operator Replacement Introduction 7 7 Last Resorts 7 7 Last Resorts 3 1 3 Restarting 6 GNU Emacs Interface runtime system version save buffers kill edwin save buffers kill scheme save editor files scheme scheme interaction mode scheme mode set set command line parser set gc notification SF version SHELL simple command line parser stack space student package version subexpression 2 1 Basics of Starting Scheme 7 2 Leaving Edwin 7 2 Leaving Edwin 7 7 Last Resorts 2 3 Memory Usage 6 GNU Emacs Interface 6 GNU Emacs Interface 4 3 2 Global variables 2 5 Custom Command line Options 3 4 Garbage Collection 4 1 Compilation Procedures 2 1 Basics of Startin Scheme 1 3 2 Environment Variables 2 6 4 Environment Variables for Edwin 2 5 Custom Command line Options 2 3 Memory Usage 2 1 Basics of Startin Scheme 5 1 Subproblems and Reductions subproblem subsystem versions suspend edwin suspend scheme system global environment TEMP TERM IMP TMPDIR IMPDIR tLogole ge notificarion trace trace both trace entry trace exit 5 1 Subproblems and Reductions 2 1 Basics of Starting Scheme 7 2 Leaving E
15. A fruitful area for inserting fixnum operations is in the index operations in tight loops lt gt L lt lt Up gt Top Contents Index 4 3 4 Flonum arithmetic Getting efficient flonum arithmetic is much more complicated and harder than getting efficient 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 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 numbers cause many temporary 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 x x y y The call distance
16. Edwin the font can be changed with the set font and set default font commands MITSCHEME GEOMETRY default 1 1 1 1 Four integers separated by commas or spaces that specify the placement and size of the MIT 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 MITSCHEME_FOREGROUND default according to desktop color scheme 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 MITSCHEME_BACKGROUND default according to desktop color scheme A value specifying the window background color See MITSCHEME FOREGROUND HOMEDRIVE HOMEPATH These variables are used together to indicate the user s home directory This is the preferred way to specify the home directory USERNAME USER 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 USERDIR Specifies a directory that contains the home directories of users One of the places in which Scheme looks for the user s home directory by searchin
17. 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 2 APPLICABILITY AND DEFINITIONS This License applies to any manual or other work that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License The Document below refers to any such manual or work Any member of the public is a licensee and is addressed as you 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 relationship 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 For example 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 w
18. PostScript PDF 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 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 Title Page means the text near the most prominent appearance of the work s title preceding the beginning of the body of the text 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 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 copying 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 4 COPYING IN QUANTITY If you publish printed copies of the Document numbering
19. Top Contents Index _ MIT Scheme User s Manual Scheme is the UnCommon Lisp This Info file is the user s guide for the MIT implementation of Scheme It describes how to install and run MIT Scheme how to execute and compile Scheme programs and how to use Scheme with Edwin and GNU Emacs Introduction 1 Installation 2 Running Scheme 3 Using Scheme 4 Compiling Programs 5 Debugging 6 GNU Emacs Interface 7 Edwin A Release Notes GNU Free Documentation License Index This document was generated by Chris Hanson on June 17 2002 using texi2html Top Contents Index _ Table of Contents Introduction 1 Installation 1 1 Unix Installation 1 2 Windows Installation 1 3 OS 2 Installation 1 3 1 OS 2 Installation Procedure 1 3 2 Environment Variables 1 4 Optional Configuration 2 Running Scheme 2 1 Basics of Starting Scheme 2 2 Customizing Scheme 2 3 Memory Usage 2 4 Command Line Options 2 5 Custom Command line Options 2 6 Environment Variables 2 6 1 Environment Variables for the Microcode 2 6 2 Environment Variables for bchscheme 2 6 3 Environment Variables for the Runtime System 2 6 4 Environment Variables for Edwin 2 6 5 Environment Variables for Microsoft Windows 2 7 Starting Scheme from Microsoft Windows 2 8 Leaving Scheme 3 Using Scheme 3 1 The Read Eval Print Loop 3 1 1 The Prompt and Level Number Sle as 4 2 canine 42 1
20. a record of expressions evaluated by the interpreter The debugger informs us that the 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 Traversing subproblems The debugger has several commands for traversing the structure of the continuation It is useful to think of the continuation as a two dimensional structure a backbone consisting of subproblems and associated ribs consisting of reductions 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 numbering older time points The u com
21. 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 implementation 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 procedure save editor files 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 procedure reset editor 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 editor That should completely res
22. 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 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 x Abort whatever Scheme evaluation is currently running and return to the current 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 running this is equivalent to evaluating cmdl interrupt abort previous 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 C Z Similar to typing quit at the REPL except that it works even if Scheme is running an evaluation C o i Ignore the interrupt Type this if you made a mistake and didn t really mean to type C c C Print help information This will describe any other options not documented here lt gt
23. break exit breakpoint breakpoints browser Continuation 5 3 Debugging Aids 4 3 2 Global variables 5 4 Advising Procedures 5 2 The Command Line_ Debugger 5 Debugging Introduction 3 1 2 Interrupting 3 1 2 Interrupting 3 1 2 Interrupting 3 1 2 Interrupting 6 GNU Emacs Interface 3 1 2 Interrupting 6 GNU Emacs Interface 6 GNU Emacs Interface 6 GNU Emacs Interface 3 1 2 Interruptin 6 GNU Emacs Interface 3 1 2 Interrupting 6 GNU Emacs Interface 6 GNU Emacs Interface 3 1 2 Interruptin 3 1 2 Interrupting 3 1 2 Interrupting cmdl interrupt abort nearest cmdl interrupt abort previous 3 1 2 Interru 7 2 Leaving Edwin 6 GNU Emacs Interface 7 2 Leaving Edwin 7 2 Leaving Edwin 3 2 Loading Files 4 1 Compilation Procedures emdl interrupt abort top level 3 1 2 Interrupting nmand scripts command line debugger 2 2 Customizing 5 2 The Com mand Line Scheme 2 1 Basics of Starting Scheme 2 1 Basics of Starting Scheme 2 1 Basics of Starting Scheme 2 6 6 Environment Variables for OS 2 constant space 2 3 Memory Usage continuation Browser 5 2 The Command Line Debugger continue 3 1 2 Interrupting create editor 7 1 Starting Edwin create editor args 7 1 Starting Edwin current REPL environment 3 1 4 The Cu
24. call Load option prior to use of hash tables For upwards compatibility calling load option hash table is still permitted but does nothing Release 7 6 1 provides a workaround for a bug on some AMD Athlon processors specifically models 1 3 and 4 This bug causes those processors to incorrectly execute certain kinds of self modifying code including that used by MIT Scheme Release 7 6 1 also fixes a problem that caused the PARSER and XML subsystems not to load correctly on Windows and OS 2 systems lt gt J s lt Up gt gt Top Contents Index _ A 2 Older Changes These are the changes that occurred between releases 7 6 0 and 7 5 17 e The variable reference machinery has been completely redesigned The new design provides two new features 1 a procedure 1ink variables that can link two variable bindings with different names previously environment 1link name could only link bindings with the same name 2 a new procedure unbind variable that can remove a variable binding Both of these operations work only on top level environments they don t work on environments created by invoking compiled procedures This is an incompatible change to the compiled code representation All programs must be recompiled e The packaging subsystem has been redesigned to make it more flexible The new design takes advantage of the improved variable linking mechanism to allow packages to export bindings usin
25. cons y cons z cons w list x y gt cons x cons y list x gt cons x list gt Declaration declare reduce operator null value 0 single group left Replacements x y Zw gt S x y Zz w C x y gt x y x gt 0 x i SATE Declaration declare reduce operator null value 0 none group right Replacements x y Zw gt St x St y z w x y gt S x y x gt x gt 0 Note This declaration does not cause an appropriate definition of in the last example to appear in your code It merely informs the compiler that certain optimizations can be performed on calls to by replacing them with calls to 3 You should provide a definition of 3 as well although it is not required Declaration declare reduce operator apply primitive cons group right wrapper global apply 1 Replacements apply f x y Zz w gt access apply cons x cons y cons Z w apply f x y gt access apply cons x y apply f x gt apply f x apply f gt apply f apply gt apply declaration reduce operator name The general format of the declaration is brackets denote optional elements reduce operator name binop group ordering null value value null option singleton unop wrapper wrap n maximum
26. 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 if environment is specified and t if environment is not specified apropos search package 47 user package 48 list search negative list search positive nt fs flag case sensitive search 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 tring search all tring search backward tring search forward ubstring search all ubstring search backward ubstring search forward vector binary search S S S S S S lt L gt lt lt Up 2 gt Top Contents Index 2 5 4 Advising Procedures Giving advice to procedures is a powerful debugging technique t race and break are useful examples of advice giving procedures Note that the advice system only works for interpreted procedures procedure 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 where vall val2 etc a
27. know what you are doing If you specify a value that is too small you can put Scheme in an unusable state procedure purify object pure space queue Moves 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 constant space immediately otherwise object is queued to be moved during the next garbage collection This argument defaults
28. link libraries blowfish dl1 gdbm d11 and md5 d11 doc Documentation files in HTML lib A directory containing the data files needed by Scheme when it is running Perform the following steps to install Scheme 1 Move the executable files scheme exe and bchschem exe from exe to any directory that appears in your PATH environment variable You may either add the exe directory to your path by editing config sys and rebooting or you may move the files in exe to an existing directory that is already on your PATH Depending on your needs you may want to keep only one of these files chances are you ll only be using one of them Of course you may also keep both programs around if you think you might use them both See section 2 3 Memory Usage for more information about the tradeoffs between these two programs 2 Move the dynamic link libraries from d11 to any directory that appears in your LIBPATH environment variable As above you may either add d11 to your LIBPATH or move the files in d11 to a directory that is already on your LIBPATH 3 You may move the 1ib directory anywhere you like You may rename it to anything you like Here at MIT we use c scheme 1ib After you have chosen where it will be located set the MITSCHEME LIBRARY PATH environment variable in config sys to be that location For example if you decide to store the directory as c schdata you
29. m where o nand m are non negative integers o name is a symbol o binop value unop and wrap are simple expressions in one of these forms constant A constant variable A variable primitive primitive name arity The primitive procedure named primitive name The optional element arity specifies the number of arguments that the primitive accepts global var A global variable o null option is either always any one single none or empty o ordering is either left right or associative The meaning of these fields is o name is the name of the n ary operation to be reduced o binop is the binary operation into which the n ary operation is to be reduced o The group option specifies whether name associates to the right or left o 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 remaining 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 o 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 o The wrapper option
30. 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 with each Opaque copy or state in or with each Opaque copy a publicly accessible computer network location containing a complete Transparent copy of the Document free of added material which the general network using public has access to download anonymously at no charge using public standard network protocols If you use the latter option you must take reasonably prudent steps when you begin distribution of Opaque copies in quantity to ensure t
31. option causes Scheme to evaluate the expressions following it on the command line up to but not including the next option 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 option 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 Sait This option causes Edwin to start immediately when Scheme is started lt gt L lt lt Up gt Top Contents Index 2 5 Custom Command line Options MIT Scheme provides a mechanism for you to define your own command line 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 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
32. 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 various 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 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 respects You may extract a single document from such a collection and distribute it individually 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 10 11 that document 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 does not as a whole count as a Modified Version of the Document provided no compilation copyright is claimed for the compilation Such a compilation is c
33. 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 o The maximum option specifies that calls with more than m arguments should not be reduced lt gt L lt lt LUp L gt gt Top Contents Index 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 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 4 3 2 Global variables 4 3 3 Fixnum arithmetic 4 3 4 Flonum arithmetic lt gt L lt lt LUp L gt gt Top Contents Index 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
34. 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 define map f lst if null lst cons f car lst map f cdr lst 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 lst cond pair lst cons f car lst map f cdr lst null lst else error Not a proper list I1st 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 There 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 a k
35. the Emacs like text editor and 6 001 is the SICP compatibility package You can load the compiler by giving Scheme the compiler option scheme compiler This option causes Scheme to use a larger constant space and heap and to load the world image containing the compiler lt gt L lt lt Up gt Top Contents Index _ 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 e Command scripts or batch files You might like 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 bat file Windows or cmd file OS 2 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 input prompt is printed This file is stored in your home directory which is normally specified by the HOME environment variable Under unix the file is called scheme init on t
36. the first byte position in the GC file at which the Scheme process can write If not given the value of the environment variable MITSCHEME_GC_START_POSITION is used and if that is not defined O is used meaning the beginning of the file The area of the file used and locked if possible is the region between gc start position and gc end position gc end position number Specifies the last byte position in the GC file at which the Scheme process can write If not given the value of the environment variable MITSCHEME_GC_END_POSITION is used and if that is not defined the sum of the start position as specified by gc start position and the heap size is used The area of the file used and locked if possible is the region between gc start position and gc end position gc window size blocks Specifies the size of the windows into new space during garbage collection If this option is not given the value of environment variable MITSCHEME_GC_WINDOW_SIZE is used instead and if that is not defined the value 1 6 is used The following command line options are only used by an experimental version of bchscheme that uses unix System V style shared memory and then only if the gcdrone program is installed in the library directory gc drone program Specifies that program should be used as the drone program for overlapped T O during garbage collection If the option is not given
37. the value of environment variable MITSCHEME_GC_DRONE is used instead and if that is not defined gcdrone is used gc read overlap n Specifies that Scheme should delegate at most n simultaneous disk read operations during garbage collection If the option is not given the value of environment variable MITSCHEME_GC_READ OVERLAP is used instead and if that is not defined 0 is used disabling overlapped reads gc write overlap n Specifies that Scheme should delegate at most n simultaneous disk write operations during garbage collection If the option is not given the value of environment variable MITSCHEME_GC_WRITE_OVERLAP is used instead and if that is not defined 0 is used disabling overlapped writes 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 scheme init or scheme ini file normally loaded automatically when Scheme starts if it exists suspend file Under some circumstances Scheme can write out a file called scheme_suspend in the user s home directory 1 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
38. 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 lt gt L lt lt Up gt gt Top Contents Index 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 amounts 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 eva
39. x C z command of GNU Emacs CH 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 command interpreter and the Scheme process is terminated This command is identical to the C x C c command of GNU Emacs lt gt lt lt Up gt gt Top Contents Index 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 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 parenthesis will temporarily flash the matching open parenthesis Most Scheme constructs requiring special indentation are recognized by Scheme mode 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
40. 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 define flo distance x y flossqrt flort fror x x Elon 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 representation 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 procedure flo vector cons n 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 pr
41. ANT MITSCHEME LARGE CONSTANT 2 4 Command Line Options 2 6 2 Environment Variables for bchscheme 2 4 Command Line Options 2 6 2 Environment Variables for bchscheme Options 2 6 2 Environment Variables for bchscheme 2 4 Command Line 2 6 2 Environment Variables for _ochscheme 2 6 5 Environment 1 3 2 Environment 2 6 3 Environment Variables for the Runtime System 2 4 Command Line Options Variables for the_ Microcode MITSCHEME LARGE HEAP MITSCHEME LARGE_HEAP MITSCHEME LARGE STACK MITSCHEME LIBRARY PATH MITSCHEME LIBRARY PATH MITSCHEME SMALL CONSTANT MITSCHEME SMALL CONSTANT MITSCHEME SMALL HEAP MITSCHEME SMALL STACK 2 4 Command Line Options 2 6 1 Environment Variables for the Microcode 2 4 Command Line Options 2 6 1 Environment Variables for the Microcode 1 3 2 Environment Variables 2 4 Command Line Options 2 6 1 Environment Variables for the Microcode 2 6 3 Environment Variables for the Runtime System 2 4 Command Line Options 2 6 1 Environment Variables for the Microcode 2 4 Command Line Options 2 6 1 Environment Variables for the Microcode 2 4 Command Line Options MITSCHEME SMALL STACK MITSCHEME UTABMD FILE MITSCHEME UTABMD FILE lt lt
42. Emacs 6 GNU Emacs_ Interface 2 3 Memory Usage 2 1 Basics of Startin Scheme 2 4 Command Line_ Options 2 6 1 Environment Variables for the Microcode 2 6 5 Environment Variables for Microsoft Windows 2 4 Command Line Options 2 6 1 Environment Variables for the Microcode 2 4 Command Line Options MITSCHEME COMPILER BAND MITSCHEME EDWIN BAND MITSCHEME GO DIRECTORI MITSCHEME_ GC DIRECTORY MITSCHEME_GC_DRONE MITSCHEME GC END POSITION MITSCHEME_GC_ FILE 2 6 1 Environment bles for the Microcode 2 4 Command Line Options Microcode 2 6 5 Environment Variables for Microsoft Windows 2 6 5 Environment Variables for Microsoft Windows 2 4 Command Line 2 6 2 Environment Variables for bchscheme 2 4 Command Line Options 2 6 2 Environment Variables for_ bchscheme 2 6 2 Environment Variables for bchscheme 2 4 Command Line Options 2 6 2 Environment Variables for bchscheme MITSCHEME GC READ OVERLAP MITSCHEME GC_READ OVERLAP MITSCHEME GC_START POSITION MITSCHEME GC WINDOW SIZE MITSCHEME GC WRITE OVERLAP MITSCHEME GC_ WRITE OVERLAP EME INF DIRECTORY MITSCHEME INF DIRECTORY MITSCHEME LARGE CONST
43. LL HEAP default 250 The size of the heap in 1024 word blocks if the size options are not given Overridden by heap large compiler or edwin MITSCHEME_SMALL_STACK default 100 The size of the stack in 1024 word blocks if the size options are not given Overridden by stack large compiler or edwin MITSCHEME_UTABMD_FILE default ut abmd bin in the library path The file containing the microcode tables Overridden by utabmd and utab lt gt L lt lt Up gt Top Contents Index _ 2 6 2 Environment Variables for bchscheme These environment variables are referred to by bchscheme not by scheme MITSCHEME GC_DIRECTORY The directory in which GC files are written Overridden by gc directory The default for this variable is the standard temporary directory see TMPDIR in see section 2 6 3 Environment Variables for the Runtime System MITSCHEME_GC_FILE default GCXXXXXxX The name of the file to use for garbage collection If it ends in 6 Xs the Xs are replaced by a letter and process id of the scheme process thus generating a unique name Overridden by gc file MITSCHEME_GC_START POSITION default 0 The first position in the GC file to use Overridden by gc start position MITSCHEME_GC_END_POSITION default start position heap size The last position in the GC file to use Overridden by gc end position
44. Shaari Names 4 3 2 Global inai 4 3 3 Fixnum arithmetic 4 3 4 Flonum arithmetic 5 Debugging 5 1 Subproblems and Reductions 5 2 The Command Line Debugger 5 3 Debugging Aids 5 4 Advising Procedures 6 GNU Emacs Interface 7 Edwin 7 1 Starting Edwin 7 2 Leaving Edwin 7 3 Scheme Mode 7 4 Evaluation 7 5 REPL Mode 7 6 The Edwin Debugger 7 7 Last Resorts A Release Notes A 1 Recent Changes A 2 Older Changes GNU Free Documentation License ADDENDUM How to use this License for your documents Index This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt lt lt Up gt gt Top Contents Index _ Introduction This document describes how to install and use MIT Scheme the UnCommon Lisp It gives installation instructions for all of the platforms that we support complete documentation 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 programs and use the editor The release notes are included as an appendix This document discusses many operating system specific features of the MIT Scheme implementation In order to simplify the discussion we use abbreviations to refer to some operating systems When the text uses the term unix this means any of the unix systems that we support including GNU Linux BSD HP UX Ultrix NeXT and SunOS Th
45. alled an aggregate and this License does not apply to the other self contained works thus compiled with the Document on account of their being thus compiled if they 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 quarter of the entire aggregate the Document s Cover Texts may be placed on covers that surround only the Document within the aggregate Otherwise they must appear on covers around 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 requires 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 provided that you also include the original English version of this License In case of a disagreement between the translation and the original English version of this License the original English version will prevail 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
46. and Line Debugger E Debugger command y Debugger command z declarations define define integrable define load option difference disk restore disk save DISPLAY edwin Edwin version EDWIN BINARY DIRECTORY EDWIN ETC DIRECTORY EDWIN_INFO DIRECTORY environments examining error ESHELL examining environments 5 2 The Command Line 4 2 Declarations 4 2 2 In line Codin 3 2 Loading Files 4 3 2 Global variables 3 3 World Images 3 3 World Images 2 6 4 Environment Variables for Edwin 7 1 Starting Edwin 7 1 Starting Edwin 2 1 Basics of Starting Scheme 2 6 4 Environment Variables for Edwin 2 6 4 Environment Variables for Edwin 2 6 4 Environment Variables for Edwin 2 6 4 Environment Variables for Edwin 5 3 Debugging Aids execution history exit exit finding procedures fixnum defn Lilotveclor cons flo vector length flo vector ref flo vector set flonum consing flush purification queue fonts free FTP site eo T lip heap space help HOME 5 2 The Command Line Debugger 2 8 Leaving Scheme 3 1 2 Interrupting 5 3 Debugging Aids 4 3 3 Fixnum arithmetic Flonum vectors Flonum vectors Flonum vectors Flonum vectors Flonum consing 3 4 Garbage Collection 2 6 5 Environment Variables for Microsoft Windows 4 3 2 Global variables Introduc
47. and is slightly different 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 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 lt gt lt lt Up 2 gt Top Contents Index 2 5 3 Debugging Aids This section describes additional commands that are useful for debugging procedure bkpt datum argument 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 J gt begin write line foo bkpt te
48. arch 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 runt ime com in these cases the library directories are searched but not the working directory large Specifies that large heap constant and stack sizes should be used These are specified by the environment variables MITSCHEME_LARGE_HEAP MITSCHEME_LARGE_CONSTANT MITSCHEME LARGE_STACK If this option isn t given the small sizes are used specified by the environment variables MITSCHEME SMALL HEAP MITSCHEME SMALL CONSTANT MITSCHEME SMALL STACK There are reasonable built in defaults for all of these environment variables should any of them be undefined Note that any or all of the defaults can be individually overridden by the heap constant and stack options Note the Scheme expression print gc statistics shows how much heap and constant space is available and in use see section 3 4 Garbage Collection heap blocks Specifies the size of the heap in 1024 word blocks Overrides any default Normally two such heaps are allocated bchscheme allocates only one and uses a disk file for the other 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 space will be available in the heap when Scheme start
49. ard 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 lt gt L lt lt Up gt gt Top Contents Index 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 xdebug showing the subproblem structure and selects the first line Each line beginning with S represents either a subprob
50. at 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 1 gc Scheme is garbage collecting When xscheme is loaded scheme mode is extended to include commands for evaluating expressions do C h min 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 xscheme 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 Cec Cs Selects the scheme buffer and places you at its end xscheme select process buffer C C y Yanks the most recently evaluated expression placing it at point xscheme yank previous send This works only in the scheme buffer The following commands provide interrupt capability C c C Like typing C g when running Scheme without Emacs xscheme send control g interrupt C c C x Like typing C c C x when running Scheme without Emacs xscheme send control x interrupt CHE C u Like typing C c C u when running Scheme without Emacs xscheme send control u interrupt C C b Like typing C c C b when running Scheme without Emacs xscheme send brea
51. ate name 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 declaration integrate operator name 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 declaration integrate external filename Causes the compiler to use the top level integrations provided 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 outputs 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 is a special form define integrable which is like define but performs
52. become unreferenced is eventually reclaimed by garbage collection e Aconstant 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 Constant 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 Scheme uses a two space copying garbage collector for reclaiming storage in the heap There are two versions of Scheme which handle garbage collection differently The standard Scheme called scheme under unix and scheme exe on the PC has two heaps one for each space An alternative called bchscheme under unix and bchschem exe on the PC has one heap and uses a disk file for the other space thus trading memory usage against garbage collection speed see section 1 4 Optional Configuration The total storage required by scheme is stack constant 2 heap extra where stack constant and heap are parameters that are selected when scheme starts For o gt chscheme which has only one heap in memory the equation is stack constant heap extra Once the storage is allocated for the constant space and the heap Scheme will dynamically ad
53. ble primitive primitive name arity The primitive procedure named primitive name The optional element 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 o 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 o If the operator has nargsN arguments then it is replaced with a call to valueN with the same arguments o If the number of arguments is not listed and one of the nargsN 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 o If the number of arguments is not listed and none of the nargsN is any else or otherwise then the operation is not replaced lt gt L lt lt Up gt Top Contents Index 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 declar reduce operator cons cons Replacements cons x y z w gt cons x cons y cons z w cons x y gt cons x y cons x gt x cons error gt too few arguments Declaration declar reduce operator list cons null value any Replacements list x y z w gt cons x
54. ce traps on all the variables except x y and any variable that is assigned to declare ignore reference traps difference all union assigned set x y m lt gt L lt lt Up gt Top Contents Index _ 4 3 3 Fixnum arithmetic The usual arithmetic operations like and lt 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 Scheme fixnums are 26 bits on 32 bit machines and 56 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 0 or 1 are guaranteed to be fixnums In addition the lengths of and valid indexes into strings and vectors 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 Scheme Reference Manual
55. d 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 procedure 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 buf fers kill scheme normally bound to C x C c and suspend scheme 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 OS 2 and Windows closing the console window Scheme s main window causes Scheme to be terminated Under any operating system closing an Edwin
56. dit 2 4 Command Line Options edwin 2 4 Command Line Options emacs 2 4 Command Line Options zemacs eval fasl GC Gi rectory gc drone gc end position gc read overlap gc start position gc window size gc write overlap 6 GNU Emacs Interface 2 4 Command Line Options 4 Command Line 2 4 Command Line Options 2 4 Command Line Options 2 4 Command Line Options 2 4 Command Line 2 4 Command Line 2 4 Command Line 2 4 Command Line 4 Command Line 2 4 Command Line Options 4 Command Line 2 4 Command Line Options 2 4 Command Line Options load 2 4 Command Line Options no init file 2 4 Command Line Options nocore 2 4 Command Line Options option summary 2 4 Command Line Options stack 2 4 Command Line Options suspend file 2 4 Command Line Options utab 2 4 Command Line Options utabmd 2 4 Command Line Options A advice 5 4 Advising Procedures advise entry 5 4 Advising Procedures advise exit 5 4 Advising Procedures all 4 3 2 Global variables apropos 5 3 Debugging Aids argument command line parser 2 5 Custom Command line Options assigned 4 3 2 Global variables band 2 4 Command Line Options band 3 3 World Images bchscheme 2 3 Memory Usage bkpt bound break break both breaker ry
57. dwin 7 2 Leaving Edwin 3 1 4 The Current REPL Environment 2 6 3 Environment Variables for the Runtime System 2 6 4 Environment Variables for Edwin 2 6 3 Environment Variables for the Runtime System 1 3 2 Environment Variables 2 6 3 Environment Variables for the Runtime System 3 4 Garbage Collection 5 4 Advising Procedures 5 4 Advising Procedures 5 4 Advising Procedures 5 4 Advising Procedures unadvise unadvise entry unadvise exit unbreak unbreak exit union Unix untrace entry untrace exit Procedures 5 4 Advising Procedures 5 4 Advising Procedures 5 4 Advising Procedures 5 4 Advising Procedures 5 4 Advising Procedures 4 3 2 Global variables Introduction 5 4 Advising Procedures 5 4 Advising Procedures 5 4 Advising Procedures 1 3 2 Environment_ Variables 2 6 5 Environment Variables for Microsoft Windows 2 6 6 Environment Variables for OS 2 3 1 4 The Current REPL Environment 2 6 5 Environment Variables for Microsoft Windows USERDIR USERNAME usbal inteyrations variable caches version numbers Web site where window color window position Windows working directory world image world image xscheme select process buffer xscheme send breakpoint interrupt 2 6 6 Environment Variables for OS 2 2 6 5 Environment Variables for Micr
58. e 1 Section One o 1 1 Subsection One One E o 1 2 Subsection One Two a 1 2 1 Subsubsection One Two One a 1 2 2 Subsubsection One Two Two a 1 2 3 Subsubsection One Two Three lt Current Position a 1 2 4 Subsubsection One Two Four o 1 3 Subsection One Three o 1 4 Subsection One Four This document was generated by Chris Hanson on June 17 2002 using texi2html
59. e GNU Free Documentation License Version 1 1 or any later version published by the Free Software Foundation with the Invariant Sections being list their titles with the Front Cover Texts being list and with the Back Cover Texts being list A copy of the license is included in the section entitled GNU Free Documentation License If you have no Invariant Sections write with no Invariant Sections instead of saying which ones are invariant If you have no Front Cover Texts write no Front Cover Texts instead of Front Cover Texts being list likewise for Back Cover Texts 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 lt lt gt gt Top Contents Index _ This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt L lt lt UpI gt gt Top Contents Index _ Index Jump to ABCDEFGHILMNOPQRS TUVW X Index Entry Section args 5 4 Advising Procedures proc 5 4 Advising Procedures result 5 4 Advising Procedures save uncompressed files 4 1 Compilation Procedures uncompressed file lifetime 4 1 Compilation Procedures band 2 4 Command Line Options c mpiler 2 4 Command Line Options Constant 2 4 Command Line Options e
60. e s data files This is the only required environment variable but is not required when Scheme is invoked with the library command line option SET MITSCHEME LIBRARY PATH C SCHEME LIB MITSCHEME_ INF_DIRECTORY tells Scheme where to find debugging information for the runtime system The default value for this environment variable is a subdirectory s rc located in the directory specified by MITSCHEME_LIBRARY_PATH SET MITSCHEME INF_DIRECTORY C SCHEME LIB SRC TMPDIR tells Scheme the name of a directory where it can store temporary files SET TMPDIR C TMP HOME tells Scheme where your home directory is located This is where Scheme looks for init files and it is also what the or filename prefix expands to If not specified Scheme uses the root directory of the current drive SET HOME C CPH USER tells Scheme your user name This is used for several purposes including the name that will be used as your email address SET USER cph SHELL tells Edwin what shell program to use in shell buffers and for running shell commands If not specified this defaults to the standard OS 2 shell cmd exe SET SHELL C 40S2251 40S2 EXE lt gt L lt lt CLUp L gt gt Top Contents Index _ 1 4 Optional Configuration As distributed Scheme contains several large files You might not need all of the
61. e term OS 2 means the IBM OS 2 operating system version 2 1 or later We use the term Windows to collectively refer to the Microsoft Windows 32 bit operating systems Windows 95 Windows 98 Windows ME Windows NT Windows 2000 and Windows XP We use the term PC to refer to any computer running OS 2 or 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 swiss ai mit edu projects scheme ftp ftp swiss ai mit edu pub 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 send email to bug cscheme zurich ai mit edu Please include the output of the identify worl1d procedure see section 2 1 Basics of Starting Scheme so we know what version of the system you are using lt lt gt gt Top Contents Index _ This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt lt lt LUp gt gt Top Contents Index _ 1 Installation This chapter describes how to install MIT Scheme release 7 7 The release is supported under several different operating systems unix OS 2 and Windows Read the section detailin
62. ecifies that Scheme should not generate a core dump under any circumstances 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 lib mit scheme On PCs the elements of the list are separated by semicolons and the default value is ce scheme lib utabmd filename Specifies that filename contains the microcode tables the microcode tables are information that informs the runtime system about the microcode s structure Filename is searched for in the working directory and the library directories If this option isn t given the filename is the value of the environment variable MITSCHEME UTABMD_FILE or if that isn t defined ut abmd bin in these cases the library directories are searched but not the working directory utab is an alternate name for the ut abmd option at most one of these options may be given fasl filename Specifies that a cold load should be performed using filename as
63. efore the Document itself or if the original publisher of the version it refers to gives permission In any section entitled Acknowledgements or Dedications preserve the section s title 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 as Endorsements or to conflict in title with any Invariant Section 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 invariant 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 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
64. emporary uncompressed version of a bci file will stay on disk after it is last used The time is in milliseconds the default is 300000 five minutes variable load debugging info on demand If this variable is f then printing a compiled procedure will print the procedure s name only if the debugging information for that procedure is already loaded Otherwise it will force loading of the debugging information The default value is f procedure sf filename destination 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 s f 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 lt gt L lt s lt Vp gt gt Top Content
65. en 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 3 1 2 Interrupting 3 1 3 Restarting 3 1 4 The Current REPL Environment SSS eee lt gt L lt lt Up gt Top Contents Index _ 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 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 gt 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
66. esponds to a block of environment variables as bound by lambda 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 command 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 To exit the REPL and return to the debugger evaluate abort gt previous oruse restart The v command prompts for a single expression and evaluates 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 env
67. et the editor to its initial state procedure reset editor windows Resets Edwin s display structures without affecting any of the buffers or their contents 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 gt lt lt gt gt Top Contents Index _ This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt J s lt Up gt gt Top Contents Index _ A Release Notes The previous full release of MIT Scheme was version 7 5 17 This section describes changes that have occurred since that time For more detailed information see the ChangeLog files in the source code Note that MIT Scheme still conforms to the Revised Report on the Algorithmic Language Scheme but not to the Revised 5 Report on The Algorithmic Language Scheme A 1 Recent Changes A 2 Older Changes lt l gt lt lt LUp gt gt Top Contents Index _ A 1 Recent Changes These are the changes since release 7 6 0 e Release 7 7 1 fixes several bugs in IMAIL fixes a bug that prevented the use of server sockets on Windows systems and fixes a bug that caused the debugger to generate errors in common circumstances e Release 7 7 0 provides hygienic macro support as defined in R4RS and R 5RS This is a complete rewrite of the syntax engine so any program that use
68. ever 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 to a given value RESTART 1 gt Return to read eval print level 2 error gt Sometimes a bug will never cause an error but will still cause the program to operate incorrectly For instance prime 7 gt In this situation Scheme does not know that the program is misbehaving The programmer 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 5 1 Subproblems and Reductions 5 2 The Command Line Debugger 5 3 Debugging Aids 5 4 Advising Procedures lt gt L lt lt LUp L gt gt Top Contents Index _
69. g names different from their internal names Also each package now maintains an in memory data structure that should in principal allow it to be uninstalled or reinstalled This subsystem is still evolving expect further changes in the future This subsystem is now included in the released binaries it can be loaded by load option cref e Compiled code debugging information is now keyed to prevent using the wrong debugging info when examining compiled code This means that in memory data structures have an identifying key that is matched against a corresponding key in the debugging info file The debugging info is used only when the keys match e MIT Scheme now has a non validating XML parser that is mostly conformant except that it doesn t support UTF 16 e There is very limited support for UTF 8 At present this is only used by the XML parser All string and character procedures now operate on ISO 8859 1 rather than US ASCII as the base character set This isn t real internationalization support but at least it broadens the character support slightly This involved changing a number of procedures that were formerly written in C and are now written in Scheme which may have a performance impact on some uses The procedure length now detects circularities in its argument and signals an error A new rexp facility provides a more readable syntax for specifying regular expressions This syntax can be compiled into the usual
70. g for a subdirectory with the user s login name lt gt L lt lt J Up gt gt Top Contents Index _ 2 6 6 Environment Variables for OS 2 These environment variables are specific to the OS 2 implementation USER Specifies the login name of the user running Scheme This is used for several different purposes If this variable is undefined an error is signalled when the username is required USERDIR Specifies a directory 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 This variable is used only when HOME is not defined we recommend using HOME rather than USERDIR COMSPEC Specifies the command shell This is set in all versions of OS 2 and is required for proper operation of the operating system Scheme uses this to determine the user s shell if the environment variable SHELL is not defined lt gt L lt lt Up gt gt Top Contents Index _ 2 7 Starting Scheme from Microsoft Windows The Microsoft Windows version of MIT 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
71. g the installation for the operating system that you are using 1 1 Unix Installation 1 2 Windows Installation 1 3 OS 2 Installation 1 4 Optional Configuration lt gt lt lt LUp gt gt Top Contents Index _ 1 1 Unix Installation We will use as an example the installation for GNU Linux The installation for other unix systems is similar MIT Scheme is distributed as a compressed tar file The tar file contains two directories called bin and 1ib The bin directory contains two executable files scheme and pchscheme The 1ib directory contains one subdirectory lib mit scheme that Scheme uses while it is executing The goal of the installation is to put the executable files in a directory where they will be executed as commands and to put the library files in some convenient place where Scheme can find them There are two ways to install this software the conventional way in usr local and the alternative way in locations of your choice We encourage you to install this software in usr local if possible To install the software in usr local do the following cd usr local rm f bin scheme bin bchscheme rm rf lib mit scheme gzip cd scheme 7 7 1 ix86 gnu linux tar gz tar xvf After executing these commands the executable files will be in usr local bin and the library files will be in usr local lib mit scheme No further configura
72. gument 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 tfogY bar takes foo scm and generates bar com About the bci files these files contain the debugging information that Scheme uses 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 dele
73. hat 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 5 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 1 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 section of the Document You may use the same title as a previous version if the original publisher of that version gives permission 2 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 less than five
74. he 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 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 e Environment variables Most microcode parameters and some runtime system and Edwin parameters can be specified by means of environment variables See section 2 6 Environment Variables e Icons Under OS 2 and Windows and with some window managers under X11 it is possible to create icons that invoke Scheme with different parameters lt gt L lt lt Up gt gt Top Contents Index _ 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 A 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
75. ibes how to run MIT Scheme It also describes how you can customize the behavior of MIT Scheme using command line options and environment variables 2 1 Basics of Starting Scheme 2 2 Customizing Scheme 2 3 Memory Usage 2 4 Command Line Options 2 5 Custom Command line Options 2 6 Environment Variables 2 7 Starting Scheme from Microsoft Windows 2 8 Leaving Scheme lt gt L lt lt Up gt Top Contents Index 2 1 Basics of Starting Scheme Under unix and OS 2 MIT Scheme is invoked by typing scheme at your operating system s command interpreter Under Windows MIT Scheme is invoked by double clicking on a shortcut In either case Scheme will load itself and print something like this Scheme saved on Monday June 17 2002 at 12 10 46 PM Release 7 7 1 Microcode 14 9 Runtime 15 1 This information which can be printed again by evaluating i1dentify 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 Runt ime 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 is the native code compiler Edwin is
76. igure shows how much memory has been used since the last garbage collection and includes all live objects as well as any uncollected 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 print gc statistics constant in use 534121 words 521 blocks 617 words constant free 128 words 0 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 procedure set gc notification on 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
77. ine other options to be loaded by load options by modifying the file opt iondb scm on the library path 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 procedure define load option symbol thunk 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 lt gt s lt Up 2 gt Top Contents Index 2 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 procedure disk save filename identify 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
78. ironment frame Continuing 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 assumptions 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 subproblem 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 comm
79. it in the system help e Under Windows NT Windows 2000 or Windows XP shortcuts can be common or personal When setting common shortcuts 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 Include absolute pathnames to scheme exe and bchscheme 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 NT 2000 XP you can use HOMEDRIVE SSHOMEPATHS to make Scheme start up in the user s home directory On Windows 9x ME you can use S HOMES to achieve the same effect provided that you have set the HOME environment variable as we recommend e There are several icons available in the Scheme executable choose one that best represents the options given on the command line e Specifying a band that contains Edwin is not sufficient to invoke the editor You also have to put edit at the end of the command line lt gt L lt lt Up gt Top Contents Index _ 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 are graphical interface buttons and their associate
80. ith 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 under this License 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 Transparent copy of the Document means a machine readable copy represented in a format whose specification is available to the general public whose contents can be viewed and edited directly and straightforwardly with generic text editors or for images composed 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 has been designed to thwart or discourage subsequent modification by readers is not Transparent 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 designed for human modification Opaque formats include
81. ized 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 Customizing Scheme procedure create editor arg 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 variable create editor args This variable controls the initialization of Edwin The following values are defined 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 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 geomet
82. just 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 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 If the size of the constant space is not specified it is automatically set to the correct size for the band being loaded Thus in general 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 lt gt L lt lt J Up gt gt Top Contents Index _ 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 If you want to define your own command line options see 2 5 Custom Command line Options These are the mic
83. kpoint interrupt C C p Like evaluating continue xscheme send proceed lt lt gt gt Top Contents Index _ This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt L lt lt Up gt gt Top Contents Index 7 Edwin This chapter describes how to start Edwin the MIT 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 Scheme while GNU Emacs extensions are written in Emacs Lisp This manual does not discuss customization of Edwin 7 1 Starting Edwin 7 2 Leaving Edwin 7 3 Scheme Mode 7 4 Evaluation 7 5 REPL Mode 7 6 The Edwin Debugger 7 1 Last Resorts lt gt L lt lt Up gt gt Top Contents Index _ 7 1 Starting Edwin To use Edwin start Scheme with the following command line options scheme edwin edit Alternatively you can load Edwin by giving the edwin command line option and then calling the procedure edit procedure edit procedure edwin 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 variable inhibit editor init file When Edwin is first initial
84. lem 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 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 Typing e creates a new buffer in which you may browse through the current environment In this new buffer
85. lt lt gt gt Top Contents Index This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt lt lt Up 2 gt Top Contents Index 2 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 breakpoints 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 When
86. luate 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 lt gt lt lt Up gt gt Top Contents Index 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 other things with the editor A REPL buffer captures all printed output from an evaluated expression as well as su
87. m so this section will tell you what each is for so that you can decide if you want to delete some of them Also we will discuss the two different Scheme executables which are each useful in different situations you should read this to decide which is right for you The Scheme runtime environment and associated tools are normally stored in bands which are large memory images stored in files see section 3 3 World Images Scheme requires at least one band to work properly The Scheme distribution includes two bands These bands are stored in the lib mit scheme directory on unix systems and the 1ib directory on PC systems runtime com The is the basic world image and the smallest It contains just the runtime files This is the band that is chosen when Scheme is invoked with no special command line options all com This contains the runtime files the native code compiler and Edwin This band is chosen when either the compiler or edwin command line options are supplied Depending on your needs you may not need both of these files For example if you always want the full development environment you might keep a11 com and delete runtime com Remember that you must keep at least one of these files to use Scheme In addition to bands Scheme is distributed with two executable programs scheme called scheme exe on PC systems and bchscheme called bchschem exe on PC systems Normally you will need
88. mand moves up to older points in time and the d command moves 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 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 currently selected subproblem or reduction The t command will reprint the standard 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 Selecting a subproblem or reduction also selects the associated environment However environments are structured as a sequence of frames where each frame corr
89. must be a string starting with a hyphen and containing at least one additional character procedure simple command line parser keyword thunk Defines keyword to be a simple command line option When this keyword is seen on the command line it causes thunk to be executed procedure argument command line parser keyword multiple 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 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 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 procedure set command line parser keyword 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 lt gt lt lt Up gt gt Top Content
90. nock 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 lst let walk lst original lst cond pair lst cons f car lst walk cdr lst null lst else error Not a proper list original lst Internal defines Internal definitions are a useful tool for structuring larger procedures However certain internal 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 The procedure returned by f1 will always give the same result and the compiler can prove this The procedure returned by 2 may return different results even if 2 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 gt 100 keep 999 gt p re define v and p p gt 999 To avoid the inefficiency intr
91. ocedure flo vector ref flonum vector index procedure flo vector set flonum vector index value procedure flo vector length flonum vector 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 0 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 1 will most likely cause a hardware error and certainly give the wrong answer f2 is correct Pitfall 2 It 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
92. oduced 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 uv 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 lt gt lt lt Up gt gt Top Contents Index 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 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 indicate 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 a
93. om on the library path The initial band to be loaded if the compiler option is given Overridden by band MITSCHEME_EDWIN_BAND default edwin com on the library path The initial band to be loaded if the edwin option is given Overridden by band MITSCHEME_LARGE_CONSTANT default as needed The size of constant space in 1024 word blocks if the large compiler or edwin options are given Overridden by constant Note the default is computed to be the correct size for the band being loaded MITSCHEME_LARGE_HEAP default 1000 The size of the heap in 1024 word blocks if the Large compiler or edwin options are given Overridden by heap MITSCHEME_LARGE_STACK default 100 The size of the stack in 1024 word blocks if the large compiler or edwin options are given Overridden by stack 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 On PC systems the list is semicolon separated with the default c scheme 1lib MITSCHEME SMALL CONSTANT default as needed The size of constant space in 1024 word blocks if the size options are not given Overridden by constant large compiler or edwin Note the default is computed to be the correct size for the band being loaded MITSCHEME SMA
94. only one of these files The only difference between these two programs is in how they handle garbage collection scheme allocates two memory heaps and copies objects between the heaps to preserve them This means that most of the time the other heap is occupying valuable memory but doesn t hold any interesting data bchscheme allocates only one memory heap creates a disk file during garbage collection copies objects into the file then copies them back into memory These programs provide you with some important performance trade offs If you have plenty of memory and want the best performance use scheme If you don t have enough memory or if you want to use less memory and will accept slower performance use bchscheme One way to tell that you don t have enough memory is to run scheme for a while and see if your machine is paging during garbage collection You might consider trying to use scheme and letting the operating system s paging handle the lack of RAM But usually you will find that using bchscheme without paging is much faster than using scheme with paging Of course if you are using bchscheme and you re still paging the best solution is to install more RAM eee lt lt gt Top Contents Index _ This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt L lt lt Up gt gt Top Contents Index _ 2 Running Scheme This chapter descr
95. onment does not belong to a package then the environment is returned lt gt s lt Up 2 gt Top Contents Index 2 3 2 Loading Files To load files of Scheme code use the procedure load procedure load filename environment syntax table purify 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 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 performs 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 binaries have pathname type com See the description of pathname type in section Components of Pathnames in MIT Scheme Reference Manual variable load noisily 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 N
96. osoft Windows 4 2 1 Standard Names 4 3 2 Global variables 2 1 Basics of Starting Scheme Introduction 5 3 Debugging Aids 2 6 5 Environment Variables for Microsoft Windows 2 6 5 Environment Variables for Microsoft Windows Introduction 3 2 Loading Files 2 4 Command Line Options 3 3 World Images 6 GNU Emacs Interface 6 GNU Emacs Interface xscheme send buffer 6 GNU Emacs Interface xscheme send control g 6 GNU Emacs interrupt Interface xscheme send control u 6 GNU Emacs interrupt Interface xscheme send cont rol x 6 GNU Emacs interrupt Interface xscheme send definition 6 GNU Emacs Interface xscheme send previous 6 GNU Emacs expression Interface xscheme send proceed 6 GNU Emacs Interface xscheme send region 6 GNU Emacs Interface xscheme yank previous send 6 GNU Emacs Interface FGHILMNOPQRS lt lt gt gt Top Contents Index _ This document was generated by Chris Hanson on June 17 2002 using texi2html Top Contents Index _ About this document This document was generated using texi2html The buttons in the navigation panels have the following meaning Button Name Go to From 1 2 3 go to order order se FastBack previous or up and previous Mo section where the Example assumes that the current position is at Subsubsection One Two Three of a document of the following structure
97. ote the noisy loading feature is implemented for source code files only variable load default types When load is given a pathname without a type it uses the value of this variable to determine what pathname types to look for and how to load the file load default types is a list of associations that maps pathname types strings to loader procedures load tries the pathname types in the order that they appear in the list The initial value of this variable has pathname types in this order Woon so we bin scm This means that for example load foo will try to load foo com first and foo scm only after looking for and failing to find the other pathname types 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 Scheme Reference Manual Files may be loaded when Scheme first starts see the 1 oad command line option for details procedure load option symbol no error Loads the option specified by symbol if already loaded does nothing Returns symbol 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 s
98. ource file runtime cpress scm Used by the runtime system for compression of compiled code debugging information format The format procedure See section Format in MIT Scheme Reference Manual gdbm Support to access gdbm databases Undocumented see the source files runtime gdbm scm and microcode prgdbm c hash table The hash table data type See section Hash Tables in MIT Scheme Reference Manual ordered vector Support to search and do completion on vectors of ordered elements Undocumented see the source file runt ime ordvec scm rb tree The red black tree data type See section Red Black Trees in MIT Scheme Reference Manual regular expression Support to search and match strings for regular expressions See section Regular Expressions in MIT Scheme Reference Manual stepper Support to step through the evaluation of Scheme expressions Undocumented 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 extensively by Edwin synchronous subprocess Support to run synchronous subprocesses See section Subprocesses in MIT Scheme Reference Manual wt tree The weight balanced tree data type See section Weight Balanced Trees in MIT Scheme Reference Manual In addition to the built in options you may def
99. p under OS 2 and Windows temp tmp and all on the system drive MITSCHEME_INF_DIRECTORY default SRC on the library path 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 MITSCHEME_LOAD_OPTIONS default opt iondb scm on the library path Specifies the location of the options database file used by the load option procedure lt gt L lt lt Up gt Top Contents Index _ 2 6 4 Environment Variables for Edwin These environment variables are referred to by Edwin EDWIN_BINARY_DIRECTORY default edwin autoload on the library path Directory where Edwin expects to find files providing autoloaded facilities EDWIN_INFO_DIRECTORY default edwin info on the library path Directory where Edwin expects to find files for the info documentation subsystem EDWIN_ETC_DIRECTORY default edwin etc on the library path Directory where Edwin expects to find utility programs and documentation strings ESHELL Filename of the shell program to use in shell buffers If not defined the SHELL environment variable is used instead SHELL default bin sh
100. 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 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 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 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
101. pporting interactive programs such as debug 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 repl 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 repl 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 Several commands allow you to access the contents of this history The command M p moves backwards through the history inserting previously evaluated expressions at point Likewise M n moves forw
102. procedures procedure untrace exit procedure Stops tracing the exit of procedure If procedure is not given the default is all exit traced procedures procedure untrace procedure Stops tracing both the entry to and the exit from procedure If procedure is not given the default is all traced procedures procedure break entry procedure Like trace entry with the additional effect that a breakpoint is entered when procedure is invoked Both procedure and its arguments can be accessed by calling the procedures proc and args respectively Use restart or continue to continue from a breakpoint procedure break exit 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 procedure break both procedure procedure break procedure Sets a breakpoint at the beginning and end of procedure This is break ent ry and break exit combined procedure unbreak 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 procedure unbreak entry procedure Discontinues the entering of a breakpoint on the entry to procedure If procedure is not given the default is all entry breakpointed procedures procedure
103. re 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 procedure trace exit procedure Causes an informative message to be printed when procedure terminates The message contains the procedure its argument values and the value returned by the procedure trace exit fib fib 3 1 lt compound procedure 19 fib Args 1 2 lt compound procedure 19 fib Args 2 3 lt compound procedure 19 fib Args 3 gt 3 procedure trace both procedure procedure trace procedure Equivalent to calling both trace entry and trace exit on procedure trace is the same as trace both trace both fib fib 3 Entering compound procedure 19 fib Args 3 Entering compound procedure 19 fib Args 1 1 lt compound procedure 19 fib Args 1 Entering compound procedure 19 fib Args 2 2 lt compound procedure 19 fib Args 2 3 lt compound procedure 19 fib Args 3 gt 3 procedure untrace entry procedure Stops tracing the entry of procedure If procedure is not given the default is to stop tracing the entry of all entry traced
104. rface library called xscheme distributed with MIT Scheme and GNU Emacs which facilitates running Scheme as a subprocess of Emacs If you wish to use this interface please install the version of xscheme e1 that comes with MIT Scheme as it is guaranteed to be correct for your version of Scheme This interface works under unix only because it requires unix signals for its operation Porting it to either OS 2 or 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 scheme 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 interact ion 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 th
105. rocode options compiler This option specifies defaults appropriate for loading the compiler It specifies the use of large sizes exactly like large if the band option is also specified that is the only effect of this option Otherwise the default band s filename is the value of the environment variable MITSCHEME_COMPILER_BAND if defined or compiler com the library directories are searched to locate this file edwin This option specifies defaults appropriate for loading the editor It specifies the use of large sizes exactly like Large if the band option is also specified that is the only effect of this option Otherwise the default band s filename is the value of the environment variable MITSCHEME_EDWIN_BAND if defined or edwin com the library directories are searched to locate this file compiler edwin If both the compiler and edwin options are given Scheme will load an environment containing both the compiler and the editor The default band s filename is the value of the environment variable MITSCHEME_ALL_BAND if defined or all com the library directories are searched to locate this file 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 se
106. rrent REPL Environment Jump to ABCDEFGHILMNOPQR S TUVW X lt lt gt gt Top Contents Index _ This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt lt lt Up gt gt Index D M Jump to A T Index Entry debug debugger Debugger command Debugger command a Debugger command b Debugger command c Debugger command d Debugger command e Debugger command f Debugger command g B CODE U VW X Top Contents Index FGHILMNOPQRS Section 5 2 The Command Line Debugger 5 2 The Command Line Debugger 5 2 The Command Line Debugger 5 2 The Command Line Debugger 5 2 The Command Line Debugger 5 2 The Command Line Debugger 5 2 The Command Line Debugger 5 2 The Command Line Debugger 5 2 The Command Line Debugger 5 2 The Command Line Debugger Debugger command h Debugger command i Debugger command k Debugger command Debugger command m Debugger command o Debugger command p Debugger command q Debugger command s Debugger command v Debugger command w Debugger command x d 2 The Command Line 5 2 The Conni F gger 52 The Coumi Debugger 5 2 The Command Line Debugger 5 2 The Command Line 5 2 The Command Line Debugger 5 y The Comodini Debugger Debugger 2 The Command Line 5 2 The Cove Debugger 5 2 The Comm
107. ry Unix only Like x except that geometry specifies the window s geometry 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 terminology 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 pm OS 2 only Creates a Presentation Manager window and uses it as Edwin s main window win32 Windows only Creates a window and uses it as Edwin s main window lt gt lt lt Up gt gt Top Contents Index 7 2 Leaving Edwin Once Edwin has been entered it can be exited in the following ways CX Z 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 Cc 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 will reinitialize the editor Cax 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
108. s Index 4 2 Declarations Several declarations can be added to your programs to help cf and sf make them more efficient 4 2 1 Standard Names 4 2 2 In line Coding 4 2 3 Operator Replacement 4 2 4 Operator Reduction lt JL gt L lt lt LUp L gt gt Top Contents Index 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 global 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 lt gt L lt s lt Vp gt gt Top Contents Index 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 declaration integr
109. s Index _ 2 6 Environment Variables Scheme refers to many environment variables This section lists these variables and describes how each is used The environment variables are organized according to the parts of MIT 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 variable EDWIN FOREGROUND 32 2 6 1 Environment Variables for the Microcode 2 6 2 Environment Variables for ochscheme 2 6 3 Environment Variables for the Runtime System 2 6 4 Environment Variables for Edwin 2 6 5 Environment Variables for Microsoft Windows 2 6 6 Environment Variables for OS 2 lt gt L lt lt Up gt Top Contents Index _ 2 6 1 Environment Variables for the Microcode These environment variables are referred to by the microcode the executable C programs called scheme and bchscheme under unix and scheme exe and bchschem exe on the PC MITSCHEME_ALL_BAND default all com on the library path The initial band to be loaded if both the compiler and edwin options are given Overridden by band MITSCHEME_BAND default runtime com on the library path The initial band to be loaded Overridden by band compiler or edwin MITSCHEME_COMPILER_BAND default compiler c
110. s 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 subsystems 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 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 bash 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 scheme lt usr cph foo in gt usr cph foo out 2 gt amp 1 amp This option is ignored under non unix operating systems nocore Sp
111. s intended to allow collecting messages into a file in a human readable format e IMAIL used to determine the type of file folders by their file names now it examines the file contents instead When creating a new file folder it prompts for the type RR lt lt gt gt Top Contents Index _ This document was generated by Chris Hanson on June 17 2002 using texi2html lt L gt L lt lt Up gt gt Top Contents Index GNU Free Documentation License Version 1 1 March 2000 Copyright 2000 Free Software Foundation Inc 59 Temple Place Suite 330 Boston MA 02111 1307 USA Everyone is permitted to copy and distribute verbatim copies of this license document but changing it is not allowed 1 PREAMBLE The purpose of this License is to make a manual textbook or other written 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 noncommercially 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 the GNU General Public License which is a copyleft license designed for free software We have designed this
112. s macros should be rewritten to use the new engine A subset of the old macro definition syntax is still supported but this will eventually be removed Note that the new syntax engine has no effect on the compiled code format most binaries compiled by release 7 6 x should continue to work There are several user visible consequences to this change o These syntactic keywords have been eliminated define macro in package macro make environment scode quote unassigned and using syntax o The syntactic keyword the environment has been restricted to use in top level environments It is no longer allowed in the body of any binding form e g Lambda let o Syntactic keywords are now stored in environments rather than in a separate syntax table structure The environment abstraction has been enhanced to support this as well as to make it more general The changes are documented in the reference manual o The syntax table abstraction has been eliminated and most procedures and arguments involving syntax tables have been removed One exception is the Load procedure which still accepts a syntax table argument but ignores it Although the 7 6 1 release had a workaround for problems with certain AMD Athlon processors the workaround was ineffective on machines running Windows operating systems and possibly OS 2 systems as well This version fixes that problem The hash table abstraction is now always loaded It s not necessary to
113. ssignment 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 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 declaration ignore reference traps variables This declaration 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 mysterio
114. st 2 test 3 write line bar done foo test 2 test 3 To continue RESTART 2 RESTART 1 2 bkpt gt Value 2 bkpt gt bar Value call RESTART with an option number gt Return from BKPT gt Return to read eval print level 1 3 3 6 continue done procedure pp object output port as code The pp procedure is described in section Output Procedures in MIT 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 host name type host cph any 15 device unspecific directory absolute usr home version unspecific 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
115. syntax There is a new parser buffer abstraction that supports the building of parsers with backtracking An associated high level parser description language allows parsers to be described in a BNF like language that is compiled into efficient Scheme code A new procedure flo finite returns f for infinite or NaN flonums and t for all others The signal handling code for GNU Linux systems has been changed to take advantage of additional information identifying the types of arithmetic exceptions This allows more accurate error messages to be generated The following procedure names were changed Old name New name list transform keep matching items positive list transform delete matching negative items list search positive find matching item and the following new procedures were implemented keep matching items anddelete matching items e IMAIL now supports commands to sort folders according to various criteria The design is similar to that of Rmail e IMAIL has been re engineered to improve performance on very large folders There is now a disk cache for each IMAP folder to eliminate unnecessary network delays Also the summary buffer previously used a quadratic algorithm to associate lines in the summary with messages in the folder it now uses a linear algorithm e Anew IMAIL command imail file message appends the text of a message to a file more or less as it appears in the buffer This i
116. tes 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 bi f file The bif file remains after Scheme exits The time interval and the behavior are controlled by the following variables variable save uncompressed files 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 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 bi f 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 variable uncompressed file lifetime The minimum length of time that a t
117. the appropriate declarations For example define integrabl 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 procedure 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 this 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
118. 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 compiler edwin or band options This option is useful only for maintenance and development of the MIT Scheme runtime system In addition to the above bchscheme recognizes the following command line options all of which specify parameters affecting how bchscheme uses disk storage to do garbage collection gc directory directory Specifies that directory should be used to create files for garbage collection If the option is not given the value of environment variable MITSCHEME_GC_DIRECTORY is used instead and if that is not defined a standard temporary directory is used see TMPDIR in see section 2 6 3 Environment Variables for the Runtime System gc file filename Specifies that filename should be used for garbage collection If the option is not given the value of environment variable MITSCHEME_GC_FILE is used and if this is not defined a unique filename is generated in the directory specified with gc directory gcfile is an alias for gc file at most one of these options should be specified gc keep Specifies that the GC file used for garbage collection should not be deleted when Scheme terminates The GC file is deleted only if the file was created by this invocation of Scheme and this option is not set gc start position number Specifies
119. 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 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 E E lt gt L lt lt Up gt Top Contents Index _ 3 1 2 Interrupting Scheme has several interrupt keys which vary depending on the underlying operating system under unix C g and C c under OS 2 and 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
120. tion is required To install the files in directories of your choice e First unpack the distribution mkdir temp cd temp gzip cd scheme 7 7 1 i1x86 gnu linux tar gz tar xvf e Next move the contents of the bin directory to somewhere convenient that is on your execution path For example if you had a directory bin on your path you would do this mv bin bin e Next move or copy the mit scheme directory somewhere convenient For example you could move it to your home directory mv lib mit scheme Note that if you have unpacked the distribution on a different drive than the one you plan to store the mit scheme directory on you must use the command cp pr rather than mv e Next you must tell Scheme where to find the mit scheme directory This can be done in one of two ways The first way is to bind the environment variable MITSCHEME_LIBRARY_PATH to the full path to the directory e g in bash you would do export MITSCHEME LIBRARY _PATH mit scheme You should put this environment variable binding in one of your shell init files e g for bash it might go in the bashrc file The second way is to use a command line argument when invoking Scheme e g scheme library mit scheme e You should now be able to run MIT Scheme See section 2 Running Scheme for more information L lt L gt lt lt LUp gt Top Contents Index _
121. tion 3 4 Garbage Collection 3 1 4 The Current REPL Environment 2 3 Memory Usage 5 3 Debugging Aids 1 3 2 Environment Variables HOME HOMEDRIVE HOMEPATH icons 1Aaentify worla ignore assignment traps ignore reference traps inhibit editor init file init file inspecting environments integrate integrate external integrate operator integrations seeing effects of intersection level number REPL level number REPL 2 6 3 Environment Variables for the Runtime System 2 6 5 Environment Variables for Microsoft Windows 2 6 5 Environment Variables for Microsoft Windows Scheme 2 1 Basics of Starting Scheme 4 3 2 Global variables 4 3 2 Global variables 7 1 Starting Edwin 2 2 Customizing Scheme 5 3 Debugging Aids 4 2 2 In line Coding 4 2 2 In line Coding 4 2 2 In line Coding Useful tip 4 3 2 Global variables 3 1 1 The Prompt and Level Number 6 GNU Emacs Interface load debugging info on demand load noisily load option load default types z O T N memory microcode version MITSCHEME ALL BAND MITSCHEME ALL BAND MITSCHEME BACKGROUND MITSCHEME BAND MITSCHEME BAND MITSCHEME COMPILER BAND 2 6 4 Environment Variables for Edwin 3 2 Loading Files 4 1 Compilation Procedures 3 2 Loading Files 3 2 Loading Files 3 2 Loading Files 6 GNU
122. to t The reason for queuing these requests is that moving an object to constant space requires a garbage collection to occur a relatively slow process By 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 procedure flush purification queue 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 procedure print gc statistics 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 f
123. 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 expression 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 to a given value RESTART 1 gt Return to read eval print level 2 error gt debug There are 6 subproblems on the stack Subproblem level 0 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 gt 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
124. usly become unbound or unassigned declaration ignore assignment traps variables 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 variable specification set name All of the explicitly listed names variable specification all variable specification none variable specification free variable specification bound variable specification assigned These expressions name sets of variables a11 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 variable specification union set set2 variable specification intersection set set2 variable specification difference set set2 For example to ignore referen
125. 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 lt gt L lt lt Up gt Top Contents Index _ 4 2 3 Operator Replacement The replace operator declaration is provided to inform the compiler that certain operators may be replaced by other operators depending on the number of arguments For example Declaration declare replace operator map 2 map 2 3 map 3 Replacements map f x y z gt map f x y zZ map f x y gt map 3 f x y map f x gt map 2 f x map f gt map f map gt 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 declaration replace operator name The syntax of this declaration is replace operator name nargsi valuel nargs2 value2 where o name is a symbol o nargsl nargs2 etc are non negative integers or one of the following symbols any else or otherwise o valuel value2 etc are simple expressions in one of these forms constant A constant variable A varia
126. vised procedure will also remove traces and breakpoints procedure advise entry procedure advice Advice must be an entry advice procedure Advice is attached to procedure so that whenever procedure is entered advice is called procedure advise exit procedure advice Advice must be an exit advice procedure Advice is attached to procedure so that whenever procedure returns advice is called procedure advice procedure 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 procedure unadvise entry procedure Removes all entry advice procedures from procedure If procedure is not given the default is all entry advised procedures procedure unadvise exit procedure Removes exit advice procedures from procedure If procedure is not given the default is all exit advised procedures procedure unadvise 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 procedures gt lt lt lt gt gt Top Contents Index _ This document was generated by Chris Hanson on June 17 2002 using texi2html lt l gt L lt lt LUp gt gt Top Contents Index _ 6 GNU Emacs Interface There is an inte
127. window causes that window to go away and if it is the only Edwin window it terminates Scheme as well Under OS 2 there are two distinct ways to close the console window The first is to use any of the usual window closing methods such as the Close system menu item or double clicking on the system menu icon When this is done you will be presented with a dialog that gives you the option to close the window with or without termating Scheme The second way is to select the Exit item from the File menu which terminates Scheme immediately with no dialog m lt lt gt gt Top Contents Index _ This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt L lt lt Up gt Top Contents Index _ 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 3 2 Loading Files 3 3 World Images 3 4 Garbage Collection lt gt L lt lt Up gt Top Contents Index _ 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 scre
128. would add the following to config sys SET MITSCHEME LIBRARY PATH C SCHDATA Remember that you must reboot OS 2 after editing config sys in order for the changes to take effect You can override the setting of this environment variable with the library command line option to Scheme for example scheme library d myscm mylib If you supply a library option it is not necessary to have the environment variable defined For example instead of editing config sys you might create a cmd file to invoke Scheme and pass it the library option automatically 4 Optional Move the doc directory anywhere you like or delete it if you do not want to keep the documentation 5 Optional Consider setting some of the environment variables described below lt gt lt lt Up gt gt Top Contents Index 2 1 3 2 Environment Variables This section documents several of the environment variables that Scheme uses and gives an example for each one These are the environment variables that must usually be defined when installing Scheme under OS 2 For complete documentation of all of the environment variables used by Scheme see 2 6 Environment Variables Note that environment variables are usually defined in the OS 2 config sys file After editing the config sys file it is necessary to reboot OS 2 before the changes will take effect MITSCHEME LIBRARY PATH says where to find Schem
129. 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 f 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 buf fer once it has been renamed it will not be automatically deleted lt gt lt lt _Up gt gt Top Contents Index _ 7 7 Last Resorts When Scheme exits
130. you should consider running with a larger heap A rough rule of thumb to halve the GC overhead is to 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 procedure toggle gc notification Toggles GC notification on and off If GC notification is turned on turns it off otherwise turns it on lt lt gt gt Top Contents Index 2 This document was generated by Chris Hanson on June 17 2002 using texi2html lt gt L lt lt LUp L gt gt Top Contents Index 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 4 2 Declarations 4 3 Efficiency Tips lt gt L lt lt Up gt Top Contents Index _ 4 1 Compilation Procedures procedure cf filename destination This is the program that transforms a source code file into native code binary form If destination is not given as in lef foom 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 ar

MIT Scheme User's Manual: MIT Scheme User's Manual

Contents

Download Pdf Manuals

Related Search

Related Contents