MIT/GNU Scheme release notes

Stable release 10.1.5

Bug: Fix problems from X11 graphics support.

Bug: Top-level definition should return the name when evaluated.

Feature: Change param:reader-fold-case? to be settable.

Stable release 10.1.4

Bug: Fix problem where Scheme crashes when running under Emacs using --emacs .

Bug: Fix breakage that caused legacy make-hash-table to throw an exception.

Feature: Implement position option for textual ports, export binary-port-position , set-binary-port-position! , and binary-port-length , and fix bug in position of binary output ports.

Feature: Allow use of bundle? as a bundle predicate. Also allow #f to be passed, meaning the same thing.

Feature: New printer parameter param:print-hash-number-in-objects? controls whether objects with #[...] printed representation will contain the hash number for the object. By default, it's true so there's no change in behavior.

Performance: Speed up string operations for Edwin and IMAIL. These changes should provide noticeable improvements.

Performance: Don't use general predicate relations for record predicates; there's no advantage, and it's far slower than just chasing the parent link.

Stable release 10.1.3

Revise unix installation notes to be more specific.

A bunch of changes to smooth the process of installation.

Bug fix: make flo:integer? answer true only for finite inputs.

Stable release 10.1.2

Fix problem: x11 plugin wasn't being recompiled when installing from native distribution.

Stable release 10.1.1

Fix problem that required a working mit-scheme when building and installing one of the distributed native builds.

Stable release 10.1

This release has a few high-level changes in addition to those detailed below:

We aren't distributing any binaries for Windows systems. The reason for this is that the 32-bit versions we've made in the past are nearly unusable in modern Windows systems, and there's a fair amount of work to get a 64-bit version that none of the current maintainers is interested in doing.

We're distributing only 64-bit binaries for macOS systems because the toolchain in recent releases has deprecated 32-bit support.

The portable C version is not included in this release because we were unable to get it working in time.

Finally, we hope to have a new point release relatively soon, since there is a long list of minor cleanups that are needed; it was felt that getting a release out was more important than making it perfect.

Major new features

R7RS ! Most of R7RS is now supported, with some exceptions: Libraries don't autoload yet; this will be added in the next release. Multiple-value returns are usable only in restricted ways. This can't be fixed without significant compiler work, which probably won't happen. Note that one of the new features of R7RS is parameters , which provide a portable way to do dynamic binding. As of this release, the use of fluid-let is deprecated; it will be removed entirely in a future release. Also note that the REPL has not changed its behavior. That's also true of the loader and the compiler, but these automatically detect when a file contains R7RS code and treats it appropriately. These changes allow existing code to continue working while new code can be written.

! Most of is now supported, with some exceptions: Support for Unicode: NFC and NFD normalization is supported; most strings are NFC. Conversions between strings and UTF-{8,16,32} bytevectors are supported. Symbols, the reader, the printer, and textual ports all support Unicode. Character sets now support Unicode, and have been significantly tuned for space, using an inversion list. New regsexp regular-expression matcher supports Unicode. The old regular-expression matcher and rexp do not. Edwin does not support Unicode.

A foreign function interface has been added to support dynamic loading of C libraries and communicating with them from Scheme. This interface has been used to replace many of the formerly hand-written interfaces to various libraries, and these are now available as plugins.

A virtual machine, svm , has been implemented and is supported as a "native code" target for building. Although fairly slow compared to native code, it has the advantage of working on any architecture. In this release we provide a 64-bit version. We're not currently providing a 32-bit version, but it can be built if needed.

SMP support

without-interrupts

without-interrupts

without-interrupts

without-interrupts

without-interruption

subprocess-global-status-tick

subprocess-status-tick

without-interrupts

without-interrupts

register-io-thread-event

register-subprocess-event

GC Notifications

*scheme*

Thread Events

The definition of block-on-io-descriptor outlines the thread event driven process underlying Scheme's multi-tasking IO. The same process can be employed to reliably block on multiple event sources. Note that without-interrupts is not needed, and was replaced by with-thread-events-blocked . (let ((state)) ; registration ids, flags shared with event handlers (dynamic-wind (lambda () (set! state (register-multiple-thread-events))) (lambda () (with-thread-events-blocked (lambda () (if (wait? state) (suspend-current-thread))))) (lambda () (deregister-multiple-thread-events state))))

outlines the thread event driven process underlying Scheme's multi-tasking IO. The same process can be employed to reliably block on multiple event sources. Note that is not needed, and was replaced by . The suspend-current-thread procedure was changed to put the thread back into an event-blocking state when it returns, as is customary for such procedures, allowing an atomic examination of the state after unblocking.

procedure was changed to put the thread back into an event-blocking state when it returns, as is customary for such procedures, allowing an atomic examination of the state after unblocking. The run-shell-command procedure now takes advantage of the ability to block on two IO channels and a subprocess status. The procedure can do fully asynchronous IO to/from the subprocess and, with output flushing, acts more like a subshell.

Minor new features

Changes to plugins: A new command line option, --prepend-library , is convenient for testing a plugin before installing it. The plugins now use libtool. Plugin package installation scripts can use procedures provided by the C/FFI to install their code and documentation. The latter can be added to compressed or uncompressed Info and HTML indices.

New library: condition variables ((mostly?) compatible with SRFI 18) (make-condition-variable #!optional name ) -> condvar (condition-variable-name condvar ) -> name (condition-variable-specific condvar ) -> object (condition-variable-specific-set! condvar object ) (unlock-thread-mutex-and-wait thread-mutex condvar #!optional timeout -ms) (condition-variable-wait! condvar thread-mutex #!optional timeout-ms ) (condition-variable-signal! condvar ) (condition-variable-broadcast! condvar )

New library: thread barriers (make-thread-barrier count #!optional name ) -> thread-barrier (thread-barrier-wait thread-barrier )

New nonrecursive with-thread-mutex-lock ; with-thread-mutex-locked is deprecated.

; is deprecated. New float functions: (flo:copysign magnitude sign ) (flo:nextafter x ) (flo:sinh x ) (flo:cosh x ) (flo:tanh x ) (flo:asinh x ) (flo:acosh x ) (flo:atanh x ) (flo:cbrt x ) (flo:erf x ) (flo:erfc x ) (flo:gamma x ) (flo:hypot x ) (flo:j0 x ) (flo:j1 x ) (flo:y0 x ) (flo:y1 x ) (flo:yn x )

New procedure (reference-barrier x ) guarantees x is not GC'd yet.

guarantees is not GC'd yet. New integer bit functions: (ffs x ) : find first set, 1-indexed with 0 for 0 (fls x ) : find last set, 1-indexed with 0 for 0 (same as integer-length ) (ctz x ) : count trailing zeros (same as ffs) ((clz n) x ) : count leading zeros in n-bit word x

New library: SHA-3 (sha3256) -> sha3 (sha3256-update sha3 buf start end ) (sha3256-final sha3 ) -> digest



Minor changes and bug fixes

Fixed weight-balanced tree balance

The SIGFPE handler was fixed so that it does not force a GC flip after every signal raised outside compiled code (e.g. in libm).

The load-noisily? variable was removed. It has been ignored for at least 10 years.

variable was removed. It has been ignored for at least 10 years. The with-thread-mutex-try-lock procedure was added for the use of GC daemons that clean a serialized data structure. They may run when a mutex is locked, cannot deadlock, and can afford to punt.

procedure was added for the use of GC daemons that clean a serialized data structure. They may run when a mutex is locked, cannot deadlock, and can afford to punt. The C/FFI now handles struct/union return values like pointer return values.

Edwin/X no longer busy-waits for the next command key. The peek-no-hang input operation takes a timeout argument allowing it to wait rather than return immediately.

input operation takes a timeout argument allowing it to wait rather than return immediately. The Edwin/X display type uses thread events (e.g. the new register-subprocess-event procedure) to reliably block without missing a subprocess status change, nor any other event on its many input sources.

procedure) to reliably block without missing a subprocess status change, nor any other event on its many input sources. A world-report procedure and a monitor-world Edwin command were added.

procedure and a Edwin command were added. The open-unix-server-socket , unix-server-connection-accept , and close-unix-server-socket procedures were added.

, , and procedures were added. A spawn-edwin procedure makes it convenient to use both an Edwin on X and a REPL on the console.

procedure makes it convenient to use both an Edwin on X and a REPL on the console. The new procedure register-time-event is analogous to register-timer-event but takes a real time instead of an interval, simplifying the effort to meet a deadline.

is analogous to but takes a real time instead of an interval, simplifying the effort to meet a deadline. The cross-reference analyzer (CREF) now supports deprecated exports, declared with an export-deprecated keyword rather than export . References to the exported bindings are noted in the analyses.

keyword rather than . References to the exported bindings are noted in the analyses. Threads can be given properties using thread-get and thread-put! . Threads can be given 'name properties and world-report will display their names. The create-thread procedure (like SRFI 18's make-thread ) now takes an optional name argument.

and . Threads can be given properties and will display their names. The procedure (like SRFI 18's ) now takes an optional argument. The FFI accepts legacy strings but returns unicode strings (or, if it encounters non-ASCII characters, bytevectors).

Incompatible changes

Most strings are now immutable! Nearly all ways of creating strings now produce immutable strings, with the exception of make-string and string-copy . Immutability provides a number of useful features, the most important being that space-efficient representations can be used. See the reference manual for full details.

and . Immutability provides a number of useful features, the most important being that space-efficient representations can be used. See the reference manual for full details. The procedure hash has been changed to be compatible with SRFI 69. Previously it was similar to object-hash , which should be used in its place now.

has been changed to be compatible with 69. Previously it was similar to , which should be used in its place now. The vector-8b procedures, which used to provide a way to access strings as vectors of bytes, are now deprecated. They don't work with the new string representation. Instead please use bytevectors for this purpose.

procedures, which used to provide a way to access strings as vectors of bytes, are now deprecated. They don't work with the new string representation. Instead please use bytevectors for this purpose. The URI accessor procedures no longer accept strings as arguments. Use ->uri to convert a string to a URI prior to using them.

accessor procedures no longer accept strings as arguments. Use to convert a string to a prior to using them. The older support for Unicode encoding forms has been removed. Please change your code to use the new bytevector converters. However, for many purposes, it is no longer necessary to handle Unicode specially since it's built in everywhere.

Experimental new features

The URI type has a new syntax: #<...> . Both the reader and the printer work with this syntax.

Stable release 9.2

Stable release 9.1

Incompatible changes

Some declarations are no more: automagic-integrations eta-substitution integrate-safely open-block-optimizations

Major new features

Ephemerons and the full range of hash table weakness options

Experimental new features

Control of the IEEE 754 floating-point environment

Interface to C libraries, and a Gtk+ binding

Rudimentary statistical profiling

Self-evaluating keyword type and notation

Swank support, somewhat flaky at the moment

Major changes

64-bit times and file offsets are mostly handled now.

A 20-year-old register allocator bug has been fixed.

Much of SF has been rewritten and some internal features removed.

Overall speed of compiled i386/x86-64 code has improved by better branches.

Primitives doing multiple allocations are less likely to wedge the GC.

Symbols can now be garbage-collected.

The syntax expander has been extensively modified which should fix many bugs.

The support for customizing write and pp has been completely revamped. The new mechanism identifies a set of objects by a universal predicate (that is, a procedure that accepts any object and returns a boolean value), which is completely general and does not depend on details of the object's representation.

Minor new features

Syntax begin0

Procedures flo:expm1 , flo:logp1

, Integer division operators

Declaration ignorable

Procedure ((constant-procedure x ) args ...) = x

Procedure (reference-barrier x ) for wrangling weakness

for wrangling weakness Operations on two's-complement representation of general integers

Unicode support in the char-set abstraction, deprecating alphabets

Unparser methods for entities

Minor changes and bug fixes

A number of obscure bugs have been fixed.

IMAIL is a little faster.

Negative (eastern hemisphere) time zones should work now.

Some archaic parts of the microcode have been garbage-collected.

Many bugs and race conditions in subprocesses have been eliminated.

Scheme handles failure of the close(2) system call correctly now.

Scheme's stack is now marked non-executable.

Termcap library selection is a little more robust.

The build system is a little more robust to interruption.

Trap handling and recovery is a little more robust.

We now do a little more automatic testing.

Wt-tree balancing has been fixed.

scheme --batch-mode no longer messes with the tty modes.

no longer messes with the tty modes. X11 support is now dynamically loadable, not a compile-time option.

Stable release 9.0

Preliminary support for symmetric multi-processing has been added, though the core functionality remains on an alternate branch. A multi-processing Scheme cannot rely onfor exclusive, atomic access to the entire system. Thusis deprecated. Many of the system's uses ofsought only to avoid interruption of a set of data structure modifications that would leave the data in an inconsistent state. These applications ofwere replaced with applications of a new procedure:. Users ofandrelied onto ensure a subprocess could not change status between examining the tick and blocking to wait for a tick. Without, these users needed another mechanism to reliably block for subprocess status changes. The IO system already does this for IO using thread events, so a procedure similar towas added:GC notifications previously ran in the after-gc interrupt handler, in whatever thread took the GC trap, or no thread at all if the thread system trapped. Unfortunately the notification procedure wants to write to a thread's dynamically bound current output port. Edwin uses this to re-direct the GC notices to itsbuffer. When the thread system trapped, a random thread's (but often the only thread's) dynamic state was used to get a current output port. In anticipation of more finely threaded (and multi-processing) worlds, all of the surprising behavior was taken out of GC notifications. Interested threads are required to register and each runs a thread event soon after the flip (like an interrupt).

(Note that we're skipping the 8.x version numbers because long ago there was an 8.x series that we never released.)

In the past my (Chris Hanson's) policy for a stable release was that the documentation had to be updated for the release before it went out. In practice, this has meant that there have been no stable releases in recent years. As of this release, we will no longer consider updated documentation a prerequisite for a stable release.

Major changes

The compiler has been ported to the x86-64 architecture, allowing Scheme programs to take advantage of very large address spaces and improved performance (due to additional registers) on that architecture.

The compiler's C back end has been resurrected, allowing the system to be run on most computer architectures (under unix-like systems only).

A new virtual machine has been designed and partially implemented. When finished, it will provide additional system portability.

The system now runs on OS X with native-code compilation.

The empty list and #f are now distinct objects.

are now distinct objects. The garbage collector has been completely rewritten. The new design uses a single heap and a temporary memory region, which doubles the largest available heap space. The now-unavailable bchscheme was similar except that its temporary region was a file.

was similar except that its temporary region was a file. There's new support for HTTP messages, and a simple HTTP client. Unfortunately none of this is yet documented.

Incompatibilities with previous releases

Support for SRFI 1 has forced a change in the behavior of the procedure reduce ; code using the old reduce should adapt to the new behavior, or use reduce-left which implements the old behavior.

1 has forced a change in the behavior of the procedure ; code using the old should adapt to the new behavior, or use which implements the old behavior. The procedure record-type-default-inits now returns a list, not a vector.

now returns a list, not a vector. The load-noisily and load-latest procedures are now just aliases for load .

System usage changes

The default configuration has been changed to reflect modern usage. Many command-line options and environment variables have been eliminated or are ignored. Specifically: The all.com band is now used by default, meaning that the compiler and Edwin are both loaded. In order to use the smaller runtime.com band, it must be explicitly specified with the --band option. The --compiler and --edwin options are now accepted but ignored. The env vars MITSCHEME_COMPILER_BAND , MITSCHEME_EDWIN_BAND , and MITSCHEME_ALL_BAND are now ignored. The default heap size is now set at 4 megawords, much larger than our previous large size, and adequate for general use. The --large option is now ignored, and all difference between large and small memory sizes is eliminated. The old MITSCHEME_LARGE_ foo and MITSCHEME_SMALL_ foo environment variables are ignored, replaced by two new vars MITSCHEME_HEAP_SIZE and MITSCHEME_STACK_SIZE . (There's no var for constant size since it's rarely necessary to specify it.)

The compiler now generates type and range checks by default, in order to make compiled code more robust. The runtime system is now compiled this way as well. New declarations (no-type-checks) and (no-range-checks) allow these defaults to be overridden. This change will cause some performance degredation; we're interested in hearing about situations in which this is a significant problem.

and allow these defaults to be overridden. This change will cause some performance degredation; we're interested in hearing about situations in which this is a significant problem. The compiler's verbosity has been significantly reduced.

The system will now run on Windows XP SP2 when the no-execute permissions are enabled.

Platform support for Cygwin has been added. This was a donation and hasn't been tested by us.

The file specified by environment variable MITSCHEME_LOAD_OPTIONS is now considered optional rather than required.

is now considered optional rather than required. The --eval and --load command-line options have been changed so that their actions are queued to be evaluated by the REPL rather than being processed outside of the REPL context. This fixes various problems with the use of these options.

and command-line options have been changed so that their actions are queued to be evaluated by the rather than being processed outside of the context. This fixes various problems with the use of these options. Several problems have been fixed in the use of modifier keys under Windows and X11.

Changes to the runtime

Defaulted optional arguments have a new value that is a self-evaluating constant. Previously such arguments were filled with a value that made them "unassigned".

cond-expand now recognizes mit and mit/gnu as features, to assist porting programs.

now recognizes and as features, to assist porting programs. The URL support has been replaced by a new implementation of URI s.

support has been replaced by a new implementation of s. Basic support for mapping of pathnames to MIME types has been added.

types has been added. There is new syntax for expression comments: #;(+ 3 4) .

. There is now support for access to the registry on Windows systems.

The low-level Unicode support has been completely rewritten: We now support UTF-8 , UTF-16 , and UTF-32 . There's a new character #\bom . Parser buffers now deal with wide characters.

The port abstraction has been completely rewritten to support character coding and a wider variety of line endings. There's a new operation to unread a character. Port encapsulation has been eliminated. discard-char is now an alias for read-char . open-tcp-stream-socket now takes only two arguments.

Hash tables have been reimplemented for improved speed. In the process some less useful operations were removed. There are new procedures make-strong-eq-hash-table and make-strong-eqv-hash-table .

and . The new procedure symbol provides an easy way to build new (interned) symbols.

provides an easy way to build new (interned) symbols. A new quoting syntax for symbols simplifies writing arbitrary symbols.

The new procedures smallest-fixnum and largest-fixnum provide the limits on the fixnum representation.

and provide the limits on the fixnum representation. The new procedure channel-file-truncate can truncate an open file.

can truncate an open file. Symbol names are now encoded in UTF-8 . string->symbol accepts an ISO 8859-1 string and converts it, while symbol->string returns an ISO 8859-1 string (or signals an error if conversion impossible). New procedures utf8-string->symbol and symbol->utf8-string provide support for UTF-8 strings.

. accepts an 8859-1 string and converts it, while returns an 8859-1 string (or signals an error if conversion impossible). New procedures and provide support for strings. string->number now accepts an optional argument; if given and true, and the input string isn't a number's representation, an error is signalled.

now accepts an optional argument; if given and true, and the input string isn't a number's representation, an error is signalled. The read procedure now accepts an optional second argument, an environment in which to look up control variables such as *parser-radix* . This allows these variables to be scoped rather than dynamically bound, which in turn makes them much safer to use. Numerous callers of read have been changed to pass an appropriate environment here.

procedure now accepts an optional second argument, an environment in which to look up control variables such as . This allows these variables to be scoped rather than dynamically bound, which in turn makes them much safer to use. Numerous callers of have been changed to pass an appropriate environment here. There are new procedures flo:rounding-modes , flo:rounding-mode , flo:set-rounding-mode! , and flo:with-rounding-mode that provide control over the floating-point rounding mode on systems that support it. Currently this is known to work on recent versions of GNU/Linux and OS X.

, , , and that provide control over the floating-point rounding mode on systems that support it. Currently this is known to work on recent versions of GNU/Linux and OS X. The random-number generator has been changed to provide reasonable output for large moduli. The previous implementation limited the amount of randomness in that case.

SRFI s 1, 2, 27, and 69 have been implemented. The procedure random-source-pseudo-randomize! from SRFI 27 has not been implemented. While I agree that this could be useful, it effectively mandates a particular PRNG , and I don't want to be forced to use it. The procedure hash from SRFI 69 has not been implemented, as it's a name conflict with a pre-existing procedure.

s 1, 2, 27, and 69 have been implemented. There is now partial support for ISO 8601 date/time strings.

8601 date/time strings. There is now basic support for RDF and Turtle.

and Turtle. There is now support for server-side programming using Apache and mod_lisp .

. There's new support for parsing compound data structures, similar to the *parser support for parsing character streams. This isn't yet documented.

Improved XML support

xml-element-content has been renamed to xml-element-contents .

has been renamed to . Character data can now be provided in several different forms.

We now support UTF-8 , UTF-16 , UTF-32 , and all ISO 8859 character sets.

, , , and all 8859 character sets. We now support XHTML 1.0 Strict and XHTML 1.1, including convenience procedures for building documents.

1.0 Strict and 1.1, including convenience procedures for building documents. We now support XML-RPC .

. XML element attributes now have an opaque representation; previously they were pairs. Also, the attribute values are now guaranteed to be strings; unresolved entity references are no longer supported.

element attributes now have an opaque representation; previously they were pairs. Also, the attribute values are now guaranteed to be strings; unresolved entity references are no longer supported. The XML naming support has been rewritten, to rationalize the code and bring our terminology into line with W3C .

Changes to Edwin

Edwin buffers are now allocated as external strings, which allows buffers to be as large as 32 MiB each.

New parenthesis-editing minor mode M-x paredit-mode .

. Support for Lisppaste.

Changes to IMAIL

IMAIL has improved sorting that works much better on large folders.

IMAIL can now parse MIME in any folder, not just in IMAP folders.

Testing release 7.7.90

As of this release, MIT Scheme is a part of the GNU project and has been renamed MIT/GNU Scheme. The project is now hosted on Savannah. License text in the source files has been changed, and a license/warranty statement is now emitted during boot, to conform to the GNU coding standards.

This is the first testing release of MIT/GNU Scheme. I had originally planned to do a stable 7.8.0 release, but time pressures have made it difficult to bring the documentation up to date, so this release comes with out-of-date documentation. Additionally, there will be binaries only for GNU/Linux; users of other systems will have to wait for the stable release.

Incompatibilities with previous releases

In releases 7.7.0 and 7.7.1, variable definitions (i.e. instances of the define special form) appearing inside let-syntax modified the environment outside of the let-syntax , while syntax definitions (instances of the define-syntax special form) modified the environment corresponding to the let-syntax form. However, according to R5RS this is incorrect: all definitions should modify the environment corresponding to the let-syntax form. The syntax has been changed to conform to R5RS .

The record abstraction has received a major update. The primary purpose of this update has been to improve the performance of constructors, and to implement keyword constructors for records. As a consequence, the representation of record types has been changed. Because record types are constructed at load time, this has no effect on previously-compiled code. However, the define-structure macro was also changed to use these new facilities. The interface between define-structure and the record abstraction was changed to increase performance, and consequently previously-compiled instances of define-structure no longer work and must be recompiled. A further change to define-structure is that the initial-value expressions are interpreted in a different way. Previously, an undocumented feature of these expressions was that they could refer to other supplied record field names as free variables. This no longer works; instead these expressions are closed in the environment in which the define-structure macro appears. The default type-descriptor name for define-structure has changed. Previously, for a structure defined as (define-structure foo bar) the type descriptor was named foo . Now, the type descriptor is named rtd:foo . This change is useful primarily because it is common to name variables that hold objects of this type foo , and when the type descriptor has the same name, it causes confusion between references to the descriptor and unintended free references to an object. (After making this change, several such free references were found in the MIT/GNU Scheme code.) Finally, define-structure now defines a type descriptor for every structure definition, including structures without tags. Previously this was done only for tagged structures.

The representation of character objects has been changed to provide direct support for Unicode. Previously, the representation had 16 bits of code and 5 bucky bits. The new representation has 21 bits of code and 4 bucky bits (the "top" bucky bit has been eliminated). This allows direct representation of the entire Unicode space. In addition, the syntax of characters has been extended to allow arbitrary Unicode characters to be represented. The new syntax is #\U+ XXXX , where XXXX is a sequence of hexadecimal digits specifying a Unicode code point. This supersedes an undocumented syntax #\<code XXXX > .

The runtime library's support for Unicode has been completely rewritten, and now has support for UTF-8 , UTF-16 , and UTF-32 encodings, as well as support for wide strings . The UTF-8 codec has been fixed to signal errors for overlong coding sequences.

The special form define-syntax has been changed so that the right-hand side may be a keyword. This can be used to make aliases for existing keywords, such as (define-syntax sequence begin)

In pre-7.7 versions of MIT/GNU Scheme, the right-hand side of the special form define-syntax was a procedure, such as (define-syntax foo (lambda ...)) This behavior was preserved in the 7.7 versions by a kludge that made the above equivalent to (define-syntax foo (non-hygienic-macro-transformer (lambda ...))) With this release, the old syntax has been eliminated. It is now necessary to use the non-hygienic-macro-transformer special form in these cases. (Note, however, that non-hygienic-macro-transformer is also a kludge and is not guaranteed to produce working macros. You should rewrite your macros in hygienic form to guarantee proper operation.)

Command-line options now start with -- rather than - , again for compliance with GNU coding standards. The older - prefix still works but may eventually be dropped.

The external representation of symbols has been extended to support the quoting mechanisms of Common Lisp. This means that there is a standard external representation for every interned symbol. For example, the notations |abcDEF| , foo|BAR|baz , and abc\ def respectively represent the symbols whose names are "abcDEF" , "fooBARbaz" , and "abc def" . This change introduces an incompatibility in the way that symbols are printed. Previously, (write symbol) was equivalent to (write-string (symbol->string symbol)) . Now, (write symbol) always writes the symbol out with appropriate quoting so that it will read back in as the same symbol.

Changes to the runtime system

A new command-line option --batch-mode disables output of banners, prompts, and values. This is intended for use with shell scripts, where the Scheme program writes to standard output and the author doesn't want the output cluttered by the interactivity cues. Note that the effect of this option applies only to the top-level REPL ; if an error occurs, all the interactivity cues are re-enabled in the error REPL .

The following SRFI s are now supported: 0, 6, 8, 9, 23, and 30.

The following newly-implemented procedures are notable: exact-positive-integer? host-big-endian? make-top-level-environment x-graphics/open-display? x-graphics/open-window?

The tcp-server-connection-accept procedure now accepts an optional argument line-translation , which sets the line translation to be used for newly-accepted sockets. (Thanks to Arthur Gleckler)

Output ports now track the current column. This is simple minded but should work for ASCII , at least.

The URI support procedures, formerly a part of IMAIL, are now in the runtime library.

Changes to Edwin

HTML mode is now used for ".xml" files, and PHP mode for ".inc" files.

VC mode has a new editor variable vc-cvs-stay-local that implements a small subset of the corresponding functionality in GNU Emacs.

The debug-on-*-error editor variables can now be set to 'ask , which causes the user to be prompted for the debugger when the corresponding error occurs. The default settings of these variables have been changed to be more appropriate for typical users.

Changes to XML support

Support for XML namespaces has been implemented. One consequence of this is that the representation of XML names has been changed. It is no longer the case that XML names can be compared with eq? ; instead one must use the new xml-name=? . Additionally, xml-intern now takes an optional second argument, which is the URI of the namespace. XML names that don't have an associated namespace URI are now ordinary interned symbols, which greatly simplifies reference to such names.

Comments are preserved by the parser.

The parser now distinguishes between <foo></foo> and <foo/> in its output. The former has a contents list of ("") , while the latter has a contents list of () .

Optional indentation is supported for DTD and attributes during output.

The parser now supports handlers for processing instructions, which are invoked during parsing. A handler maps the text of a processing instruction to a list of XML items, which are inserted into the resulting XML structure in place of the processing instruction.

The following new procedures are available to make XML input and output more convenient: read-xml read-xml-file write-xml-file string->xml substring->xml xml->string xml->wide-string

All the remaining bugs identified by the XML conformance tests have been fixed, except support for UTF-16 .

Stable release 7.7.1

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.

Stable release 7.7.0

This release provides hygienic macro support, as defined in R4RS and R5RS . This is a complete rewrite of the syntax engine, so any program that uses 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.

User-visible consequences to this change

These syntactic keywords have been eliminated: define-macro in-package macro make-environment scode-quote sequence unassigned? using-syntax

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 ).

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.

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.

Other notable changes in this release