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PC Scheme Version 3.03 Release Notes
This document describes the changes in PC Scheme since version 2.0.
PC Scheme 3.0 features
----------------------
Version 3.0 contains bug fixes, significant enhancements over 2.0, and
has been upgraded to the latest Scheme Standard as defined by the "Revised
Revised Revised (R^3) Report on the Algorithmic Language Scheme." A copy
of that report is now included in the 3.0 manuals.
Also included in this document is a number of features which are not
documented in the Language Reference Manual nor the User's Guide, but
which may be useful for programming.
R^3 Report Changes
------------------
1. #T and #F now replace #!TRUE and #!FALSE. #!TRUE and #!FALSE are
still supported in 3.0, however their use is discouraged and they
may not be supported in future versions.
2. Quasiquote expressions may now be nested and are defined to work
with vectors. The keywords UNQUOTE (",") and UNQUOTE-SPLICING (",@")
are also now recognized.
3. The defining form (DEFINE (<variable> <formals>) <body>) no longer
expands into a NAMED-LAMBDA as specified in the Report. To support
code written under earlier versions of Scheme, the global variable
PCS-INTEGRATE-DEFINE may be set non-nil to force the expansion, or
nil to conform to the Report. Its default value is #T.
4. BOOLEAN? is a new procedure which indicates if an object is either
#T or #F (ie., (BOOLEAN? #T) => #T).
5. PROCEDURE? is a new procedure which indicates if an object is a
procedure (ie., (PROCEDURE? CAR) => #T).
6. The expression types NAMED-LAMBDA, REC, and SEQUENCE have been removed
from the Report but will continue to be supported as extensions.
7. The following procedures have been removed from the report, however
they will continue to be supported as extensions:
APPEND!, STRING-NULL?, SUBSTRING-FILL!, SUBSTRING-MOVE-LEFT!,
SUBSTRING-MOVE-RIGHT!, OBJECT-HASH, OBJECT-UNHASH, 1+, -1+.
8. The redundant procedure names <?, <=?, =?, >?, and >=? have been removed
from the Report and will be supported in this release, however their use
is discouraged and future versions may not support them.
9. The syntax #!NULL (for the empty list) has been removed from the report.
Its usage is also discouraged and may not be supported in the future.
Bug Fixes
---------
1. DEFINE has been corrected to bind a variable in the correct environment.
Earlier versions of PCS could incorrectly rebind variables defined in
parent environments, if the variable did not exist in the defining
environment.
2. IMPLODE now flags an error if given a non-list object.
3. NUMBER->STRING has fixes to correct problems with the '(heur) format.
4. Shift/Break now correctly halts printing of circular lists.
5. INPUT-PORT? and OUTPUT-PORT? have been corrected to return '() after the
port is closed.
6. Expanded Memory Scheme no longer requires the EMM page frame to be on a
64kb boundary.
7. Drawing a line from x1,y1 to x2,y2 and later erasing it in the
direction x2,y2 to x1,y1 now correctly resets all the intermediate
pixels.
Enhancements/New Features
-------------------------
1. Graphics has undergone significant changes which are documented in the
User's Guide and Language Reference Manual. Following is a synopsis of
the changes:
* The %GRAPHICS primitives now accept a seventh argument to specify
an exclusive-or when drawing pixels or lines.
* A new %GRAPHICS function has been included which allows you to set
a clipping rectangle which subsequent drawing functions use. All
%GRAPHICS drawing routines now use the clipping rectangle.
* New graphics functions:
(GET-PEN-COLOR) - returns the pen's color.
(GET-PEN-POSITION) - returns the pen's position.
(POINT-COLOR) - returns a point's color value.
(SET-CLIPPING-RECTANGLE! x1 y1 x2 y2) - set clipping rectangle.
* Modes 14 and 16 for the EGA are now supported.
* CLEAR-GRAPHICS no longer automatically switches into mode 4, but
remains in the current video mode. SET-VIDEO-MODE! will automati-
cally do a CLEAR-GRAPHICS after changing modes.
2. EDWIN contains several changes to help in its performance and flexibility.
* The file EDWIN.INI will be loaded if it exists within the PCS
directory. EDWIN.INI may contain code to customize the display,
or remap the keyboard. See EDWIN.INI for examples.
* Edwin now loads into its own environment, EDWIN-ENVIRONMENT. This
reduces the number of variables in the USER-GLOBAL-ENVIRONMENT and
allows EDWIN to be removed via the new REMOVE-EDWIN command.
* REMOVE-EDWIN is a procedure of no arguments which may now be called
to remove references to EDWIN so that it will disappear upon the
next garbage collection. Remember that if EDWIN was loaded from
SCHEME-TOP-LEVEL, the history will still contain pointers to EDWIN,
prohibiting it from being garbage collected. In that case, you must
perform a SCHEME-RESET prior to the garbage collect to remove all
references to EDWIN.
* EDWIN will now query the user upon exiting Scheme, if its buffers
have been modified but not written back out to the file.
* The time required to load files into EDWIN's buffer has been
significantly reduced.
3. PC Scheme now contains an External Language Interface (XLI) to support
the calling of subroutines written in other languages. XLI has been
tested to work with assembly, C and Pascal. See the chapter "External
Language Interface (XLI)" in the User's Guide for more information.
4. Transcendental functions have been rewritten using XLI and
use the 8087/80287 numeric coprocessor when it is available.
Accuracy is true double-precision and performance is significantly
improved, even without the 8087. The complete source code of this
XLI interface is included. Refer to the chapter "External Language
Interface (XLI)" in the User's Guide for more information.
5. A semi-interpretive EVAL has been implemented. EVAL now works
interpretively until it encounters a binding form (such as LAMBDA,
LET, etc.), at which time the compiler will be invoked.
6. READ-LINE has been implemented as a primitive operation and will now echo
to the screen when called to read from the console.
7. LIST-TAIL has been implemented as a primitive operation. Both LIST-REF
and LIST-TAIL gain significant performance increases.
8. Random I/O is now supported via SET-FILE-POSITION! and GET-FILE-POSITION.
See the description in the Language Reference Manual.
9. Binary file input and output is now supported via OPEN-BINARY-INPUT-FILE
and OPEN-BINARY-OUTPUT-FILE procedures. See the description in the
Language Reference Manual.
10. The non-essential procedure STRING->NUMBER from the R^3 Report is now
included. See the description in the Language Reference Manual.
11. #\ESCAPE has been added as a system defined character.
12. Enhanced error handling is now available, and DOS I/O errors now trap
to the inspector, with extended error information available. Reference
the User's Guide under the chapter "DEBUGGING" for information on
defining your own error handler via *USER-ERROR-HANDLER*.
13. New procedures EXPAND-MACRO-1, EXPAND-MACRO, and EXPAND. EXPAND-MACRO-1
will expand the outer-level of some form once and return the expanded
form, EXPAND-MACRO will repeatedly expand the outer-level form until it
is no longer a macro, and EXPAND will expand the entire form (outer and
inner level forms), returning an expansion.
Example: (EXPAND-MACRO '(let ((a 1) (b 2)) (foo a b)))
*** Note ***
When expanding various forms with the above procedures, you may
encounter references to primitive operations. These primitive oper-
ations typically begin with one or more percent signs (%), are
generally not available for direct use by the user, and may change
in future versions of PC Scheme.
14. The random number generator can be reseeded using the RANDOMIZE
function. See the description in the Language Reference Manual.
Corrections to the Manuals
--------------------------
The following corrections to the User's Guide should be noted.
1. At the top of page 8-16, the request number to be used for the
"swap" special service request was omitted. The bullet that reads:
* swap
should be replaced with:
* swap (request number = 1)
2. On page C-1 the symbol "remap" is equated with interrupt 7fh.
However, the comment just below it refers to interrupt 60h.
The correct interrupt number is 7fh. Therefore, the comment that reads:
; This example uses the interrupt at 60h; refer to ...
should be replaced with:
; This example uses the interrupt at 7fh; refer to ...
Undocumented/Non-Standard Features
----------------------------------
The following features are undocumented features which may or may not be
supported in future releases. They certainly are not standard Scheme
features and prohibit portability, but may be useful in some cases.
1. GRAPHICS-WINDOW is a function which may be useful in creating graphics
windows. It is currently in an experimental stage, is not fully complete,
and is subject to change. Still, it is useful in its current form, and
you may try it out at your own risk.
GRAPHICS-WINDOW is a "marker" function indicating that the next series
of MIT graphics functions will execute relative to a specified window
instead of the full screen. It takes one argument, a window object
(a port), and returns a 2-list of 4-lists. The first list is the
clipping rectangle for the window's interior using window-centered
coordinates, expressed as (left top right bottom), for use by the MIT
functions, and the second list is the same rectangle expressed in
screen coordinates for use by %GRAPHICS. It changes the graphics
state known by the MIT functions and sets the clipping rectangle to
correspond to the window's interior so that further use of the MIT
functions will execute relative to the window instead of the full screen.
Aside from setting the clipping rectangle, there are no other effects
on %GRAPHICS.
After executing GRAPHICS-WINDOW on a window for the first time, a call
to CLEAR-GRAPHICS should be issued to set the pen position and color
and erase the graphics plane under the window (which may erase text
too if they share the same plane). Further graphics commands are
issued normally.
To move from one graphics window to another, use GRAPHICS-WINDOW with
the next window. Note that when you move to another window, the graphics
state (window, pen color, and pen position) of the first window is
forgotten. You will need to save it off if you want to come back and
start up where you left off. The functions CURRENT-GRAPHICS-WINDOW,
GET-PEN-COLOR, and GET-PEN-POSITION, executed before the switch, will
give you this information.
While executing relative to a window, CLEAR-GRAPHICS will not affect
the entire screen. To reset CLEAR-GRAPHICS to its initial state
where it does affect the entire screen, do (GRAPHICS-WINDOW 'SCREEN)
followed by (CLEAR-GRAPHICS). Executing SET-VIDEO-MODE! any time will do
this automatically. Note that (GRAPHICS-WINDOW 'SCREEN) is not the same
as (GRAPHICS-WINDOW 'CONSOLE); although the console generally matches the
screen, it doesn't have to--it's a window in its own right.
2. %LOGAND, %LOGIOR, %LOGXOR are procedures of two arguments and are used
to perform the bitwise logical operations and, or, and xor. The
arguments must be 15 bit integers.
3. UNBIND is a procedure which may be used to remove bindings from
environments. The call to unbind is as follows:
(UNBIND 'VAR ENV)
Where : VAR is the variable you wish to remove
ENV is any heap allocated environment, including the
user-initial and user-global environments.
Unbind can be useful in providing user-assisted memory management.
If an object which is auto-loadable is unbound via the UNBIND
procedure, it may later be auto-loaded again. Therefore, if you
define autoload lists, you can maintain some control over what
code you desire in memory.
4. Autoload information created from the function AUTOLOAD-FROM-FILE (see
chapter titled "ADVANCED FEATURES" in User's Guide) is stored on a
property list under the name PCS-AUTOLOAD-INFO. Scheme defines a number
of autoload entries of its own, and any that you add will be consed
onto the autoload list. You can see the autoload information by
performing (GETPROP 'PCS-AUTOLOAD-INFO).
The procedure AUTOLOAD-FROM-FILE also takes an optional third argument
which indicates the environment that you want the file loaded into. For
example
(autoload-from-file "DEFS.FSL" '(foo bar baz) user-initial-environment)
will load the file "DEFS.FSL" into the user-initial-environment whenever
foo, bar, or baz is referenced. The optional environment argument can
be any heap allocated environment. To add or delete entries from the
autoload list just write your own functions to modify the list, however
if you remove any of the compiler dependent files from the list, a
reference to one of its functions will cause errors.
The undocumented procedure REMOVE-AUTOLOAD-INFO may be used to remove
information from the autoload list. REMOVE-AUTOLOAD-INFO takes one
argument, the filename of the autoload entry you wish to remove, and
then removes the autoload information from the list. This function,
along with UNBIND can be used to help the user perform memory manage-
ment.
5. MAKE-HASHED-ENVIRONMENT is a procedure of no arguments which creates
an environment in the Scheme heap in the form of a hash table for
better accessing. The hash table contains 211 entries; any time a
variable is defined in that environment a hash key will be determined
via an internal hash function to find the correct entry. This is
identical to the user global and user initial environments. A hashed
environment's parent is the user-initial-environment.
A hashed environment will provide better access times than normal
environments, given there are a lot of variables in the environment.
However, there is certainly a space/time tradeoff to consider. The
hashed environment contains much more overhead which will be wasted
if you need only a handfull of variables.
One advantage of the hashed environment, as with all environments,
is that if you discard all references to the environment, it will
be garbage collected and all the space may be reclaimed. This means
that you must keep track of all variables or references which are
exported to other environments. Also, if you define a macro within
an environment, the macro definition holds a reference to the
environment and will prohibit garbage collection of the environment.
Macro definitions may be found under the property PCS*MACRO of the
macro name declared.
6. While the 3.0 implementation of transcendental functions is much
faster and more accurate and therefore to be preferred, the 2.0
version had the advantage of being about half the size. If space is
more important than speed or accuracy, you can do the following:
1. Invoke PC Scheme as usual, except put a minus sign in front
of the .XLI control file name; this prevents XLI from
loading NEWTRIG.EXE. For example:
pcs (my.ini -my.xli) arg1 arg2
2. Inside PC Scheme, do:
(eval '(load "oldpmath.fsl") user-global-environment)
If your current directory is not the PC Scheme directory,
you'll need to append the value of the system variable
PCS-SYSDIR to the front of the filename. The LOAD must be
inside the EVAL so that autoload references to pmath.fsl
will be intercepted correctly.
It is not absolutely necessary to do step 1 just to use oldpmath.fsl,
but the space savings won't be realized without it. Also, step 2
should be done soon upon entering PC Scheme, as various system
functions, such as some Edwin commands, require the math functions
(whether through XLI\pmath.fsl or through oldpmath.fsl) to be loaded.
PC Scheme 3.02 features
-----------------------
The following bugs have been fixed.
1. There were several obscure bugs in the extended and expanded memory
models of PC Scheme which have been corrected. Also, extended memory
performance has been enhanced by about 25%.
2. PC Scheme 3.02 recognizes an IBM PS/2 Model 80. IBM has assigned
a new machine-type number to it, which is reflected in the value
of PCS-MACHINE-TYPE. More importantly, FREESP in extended memory
PC Scheme now works correctly on the Model 80.
3. EQUAL? on ports no longer causes a type mismatch error.
4. There was a bug in determining the pathname of NEWTRIG.EXE when
PC Scheme had been installed in the root directory. This usually
showed itself when running PC Scheme from floppy disks.
5. In the form (SET! (ACCESS var env) value), there was a bug in which
environment the "value" was placed if the "var" did not already exist.
6. DOS-CALL no longer depends on the COMSPEC environment variable
being listed first in the DOS environment.
7. Line-lengths for binary files are now automatically set to zero
so end-of-line sequences are suppressed.
8. XLI checks for its version number. PC Scheme 3.02 uses the same
version number as 3.0. The error message is "[XLI] Version mismatch".
Also, the XLI error message "[XLI] The function requested by XCALL is not
available" now is followed by the name of the function that failed.
10. PC Scheme's definition of EQV? says "=" is used to compare numeric
arguments. However, MEMV and ASSV, which are supposed to use EQV?
for their equality predicates, were really using EQUAL?. "=" and
EQUAL? return different results when two numeric arguments have
different types, so the fix may cause a change of behavior in how
MEMV and ASSV work.
11. Internal "getmem" errors no longer cause an abort to DOS.
Instead, the system performs a SCHEME-RESET. The error generally
appears during output of extremely large data structures when
I/O buffer space is exhausted, but the data structures themselves
remain intact, so this should be adequate recovery in most cases.
12. A bug in SCOOPS was making the environments in which instance
variables got created be dependent on the order in which the
classes were compiled.
The following features are "new" to PC Scheme 3.02.
1. XLI can now receive error messages from external programs and drop into
the Inspector displaying the error message.
The external program reports an error as follows. It formats the
parameter block with a string as return value, where the string is
the error message. However, instead of using a return-value type of
2 (string), it should use a value of 10 (error-string). XLI will
drop into the Inspector with the error message "[XLI] Error reported
by external program" followed on the next line by the external
program's error message (note the Inspector uses WRITE to display
the message). The error is not restartable.
If an external program using this error technique is run under
PC Scheme 3.0, XLI reports the different error "[XLI] The return value
of XCALL is invalid" and the external program's error message never
appears.
NEWTRIG.EXE has been reimplemented with this technique. Refer to
the file XLI\TRIG_LC.C to examine the source code.
2. There are a couple more XLI source examples in the XLI directory.
One is in assembly language, the other in C. One provides PC Scheme
with sound capability, and the other demonstrates a way to run
DOS-executable files without using DOS-CALL.
3. %GRAPHICS for EGA has been reimplemented to do direct screen writes.
This gives a significant performance boost at the expense of generality,
which may affect some EGA clones. Also, VGA modes 17 and 18 are now
supported.
PC Scheme 3.03 features
-----------------------
The following bugs have been fixed.
1. Random I/O has been fixed. If a file is opened with OPEN-EXTEND-FILE,
one can perform both input from and output to that file.
2. An obscure garbage collection bug was fixed which envolved one defining
their own top-level. If a user top-level has been defined instead of
the Scheme-Top-level, and an out of memory encountered an error message
occurred on the next garbage collect.
3. A garbage collection bug in extended memory was fixed. Compaction of
list cells could sometimes cause problems.
4. A problem with DOS memory fragmentation was fixed. Upon returning from
PC Scheme, all of memory was not being returned to DOS. This could some-
times cause other programs to fail with "not enough memory" errors.
The following new features have been added:
1. Support has been added for VGA mode 18.
2. One can now specify when garbage compaction should occur.
(GC-GET-COMPACT-COUNT! number) - specifies that a compaction should
occur after every "number" of gc's.
(GC-GET-COMPACT-COUNT) - returns the current "number".

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