MIT/GNU Scheme release notes
Stable release 9.2
Stable release 9.1
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
- 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.
Minor new features
- Integer division operators
((constant-procedure x) args ...) = x
(reference-barrier x)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-modeno longer messes with the tty modes.
- X11 support is now dynamically loadable, not a compile-time option.
Stable release 9.0
(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.
- 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
#fare 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
bchschemewas 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
reduce; code using the old
reduceshould adapt to the new behavior, or use
reduce-leftwhich implements the old behavior.
record-type-default-initsnow returns a list, not a vector.
load-latestprocedures are now just aliases for
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:
all.comband is now used by default, meaning that the compiler and Edwin are both loaded. In order to use the smaller
runtime.comband, it must be explicitly specified with the
--edwinoptions are now accepted but ignored. The env vars
MITSCHEME_ALL_BANDare now ignored.
- The default heap size is now set at 4 megawords, much larger than our previous large size, and adequate for general use.
--largeoption is now ignored, and all difference between large and small memory sizes is eliminated. The old
MITSCHEME_SMALL_fooenvironment variables are ignored, replaced by two new vars
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-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.
- 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_OPTIONSis now considered optional rather than required.
--loadcommand-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.
- 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".
mit/gnuas features, to assist porting programs.
- The URL support has been replaced by a new implementation of URIs.
- Basic support for mapping of pathnames to MIME 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:
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-charis now an alias for
open-tcp-stream-socketnow takes only two arguments.
Hash tables have been reimplemented for improved speed. In the
process some less useful operations were removed. There are new
The new procedure
symbolprovides an easy way to build new (interned) symbols.
- A new quoting syntax for symbols simplifies writing arbitrary symbols.
The new procedures
largest-fixnumprovide the limits on the fixnum representation.
The new procedure
channel-file-truncatecan truncate an open file.
Symbol names are now encoded in UTF-8.
string->symbolaccepts an ISO 8859-1 string and converts it, while
symbol->stringreturns an ISO 8859-1 string (or signals an error if conversion impossible). New procedures
symbol->utf8-stringprovide support for UTF-8 strings.
string->numbernow accepts an optional argument; if given and true, and the input string isn't a number's representation, an error is signalled.
readprocedure 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
readhave been changed to pass an appropriate environment here.
There are new procedures
flo:with-rounding-modethat 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.
SRFIs 1, 2, 27, and 69 have been implemented.
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.
hashfrom SRFI 69 has not been implemented, as it's a name conflict with a pre-existing procedure.
- The procedure
- There is now partial support for ISO 8601 date/time strings.
- There is now basic support for RDF and Turtle.
There is now support for server-side programming using Apache and
There's new support for parsing compound data structures, similar to
*parsersupport for parsing character streams. This isn't yet documented.
Improved XML support
xml-element-contenthas 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.
- We now support XHTML 1.0 Strict and XHTML 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.
- 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
- 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
definespecial form) appearing inside
let-syntaxmodified the environment outside of the
let-syntax, while syntax definitions (instances of the
define-syntaxspecial form) modified the environment corresponding to the
let-syntaxform. However, according to R5RS this is incorrect: all definitions should modify the environment corresponding to the
let-syntaxform. 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.
define-structuremacro was also changed to use these new facilities. The interface between
define-structureand the record abstraction was changed to increase performance, and consequently previously-compiled instances of
define-structureno longer work and must be recompiled.
A further change to
define-structureis 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
The default type-descriptor name for
define-structurehas 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.)
define-structurenow 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 #\<codeXXXX>.
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-syntaxhas 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-syntaxwas 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-transformerspecial form in these cases. (Note, however, that
non-hygienic-macro-transformeris 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 SRFIs 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?
tcp-server-connection-acceptprocedure 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
VC mode has a new editor variable
vc-cvs-stay-localthat implements a small subset of the corresponding functionality in GNU Emacs.
debug-on-*-erroreditor 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-internnow 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-environmenthas been restricted to use in top-level environments. It is no longer allowed in the body of any binding form (e.g.
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
loadprocedure, which still accepts a syntax-table argument, but ignores it.
Other notable changes in this release
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 call
load-optionprior to use of hash tables. For upwards compatibility, calling (load-option 'hash-table) is still permitted but does nothing.