home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Power-Programmierung
/
CD1.mdf
/
forth
/
compiler
/
fpc
/
doc
/
chapter9.txt
< prev
next >
Wrap
Text File
|
1989-10-29
|
23KB
|
529 lines
CHAPTER 9. ADVANCED UTILITIES
9.1. REBUILDING THE SYSTEM
If you need to change a parameter or function in the F-PC system, you
will need to re-compile F- PC and/or KERNEL. This is simply done with
the provided batch files as follows:
C> FMETA <enter> Re-compiles KERNEL.COM
C> EXTEND <enter> Re-extends to create F-PC.EXE
Either of these may be performed from the keyboard while in DOS. FMETA
invokes F-PC, loads the meta compiler, and recompiles the kernel. The
resulting new kernel is stored back as KERNEL.COM. Utilities and
applications are then compiled on the top of KERNEL by EXTEND to generate
a new F-PC system.
To extend the F-PC system with your application, edit the F-PC.SEQ file
to include FLOAD instructions to load your application files. You may
want to change the name of the EXE file finally saved. This can be done
by editing the filename after the SAVE-EXE statement in F- PC.SEQ file.
Meta compilation the the darkest art in Forth. Do not be fooled by the
above simple discussions to think that meta compilation can be practiced
easily. You have to understand F-PC completely to made modifications in
the kernel files to rebuild a Forth to your own liking. Only Tom Zimmer
is entrusted to make modification to F-PC. Nevertheless, you have all
the source code and the tools to roll your own Forth in F-PC.
9.2. TURNKEY SYSTEMS
The word TURNKEY and some associated words are included in the file
SAVESYS.SEQ. TURNKEY is used as follows:
' MYAPPL IS DEFAULT TURNKEY MYAPP <enter>
After completing an application compile, the word MYAPPL is defined to be
performed by the program name MYAPP.COM. TUNRKEY automatically sets up
the proper memory management to allocate 64k for your program, but does
not save the heads. Minimum initialization is performed. A file
specified on the command line will be opened, and you can use BL WORD to
pick up additional parameters from the command line. You will of course
not be able to interpret, since heads are not saved, and your application
will need to handle all errors and return to DOS when the program
completes.
Before attempting to build an application, you will need to make a copy
of F-PC.SEQ, for customization. Many of the later files in F-PC.SEQ are
utilities, and will not be needed in your application. Start by writing
your program and compiling it on F-PC.EXE. Work in this environment
until you are sure your program works. Now insert your program filename
into the copy of F-PC.SEQ you made, about half way down, and try to
compile the copy of F-PC.SEQ. If it compiles then you can move your
application file lower, until you have determined what utilities are
needed by your application. Strip out all files above your application
file, and load the file SAVESYS.SEQ. Use TURNKEY as previously described
to make an executable .EXE file.
TURNKEY allow you to customize F-PC to build an independent application,
which may not allow the user to see the internal of the application. If
you are not so protective, a more convenient way to generate an
application is to use FSAVE, which saves the core image of F-PC after you
have loaded your application. F-PC is included inside your application
and the user have access to the entire system. This is a useful tool as
you can make a snapshot of your current system, save it to the disk, and
have it available the next time you resume your work. The commands are:
FSAVE MYSYSTEM <return>
A file MYSYSTEM.EXE is saved in your current directory which contains
everything you compiled so far. Next time when you execute MYSYSTEM
under DOS, your current system will be loaded and F-PC will be at your
service.
9.3. MACROS IN F-PC AND SED
A file called MACROS.SEQ is provided,. This file implements keyboard
macros in Forth at the level of KEY. These macros can therefore be used
in the editor also. The macros are used as follows: (the sequence
"Alt-M" means hold down the "Alternate" key and press the "M" key.)
Alt-M Start defining a macro.
Alt-1 We are defining the Alt-1 macro.
Enter any keys you want in the macro, up to 128 keys.
Alt-M Complete the definition of the Alt-1 macro.
Any keys available on the keyboard except Alt-m, and Alt-1 to Alt-5 can
be included within a macro. To execute a macro, simply type its key
name:
Alt-1 Execute the macro key sequence for the Alt-1 key.
Currently macros may be only 127 characters in length, although this can
be changed by modifying the constant MAXMAC and recompiling the system.
See the example in Appendix B-3.
9.4. F-PC PREFERENCES
While F-PC may seem like a nebulous glob of stuff, some things about it
can be adjusted fairly simply. The install process, for example, allows
you to tell F-PC where its source file will be located, whether you want
to have backup copies made of your edited files, and what you want to
call your installed version of F-PC. There are however a number of other
things you might like to adjust to your personal way of doing things.
Here is a list:
The status line display may be turned on/off.
STATON Enable status line display at top of screen.
STATOFF Disable status line display.
The decompile display during debugging may be turned on/off.
SRCON Source display enabled during debug.
SRCOFF Source display disabled during debug.
The default file extension for the system and the file specification
string for the popup window file selector may be changed.
DEFEXT Default file extension string.
HIDDEN DIRSPEC$ Directory specification for popup window.
The format of date printing can be adjusted to one of the three supported
formats, or you can add your own.
M/D/Y Month/Day/Year (default format)
Y-M-D Year-Month-Day
D.M.Y Day.Month.Year
You can manually turn editor backups on or off without going through the
install process.
BACKUPOFF Disables the editor from making backup files.
BACKUPON Enables the keeping of editor backup files.
F-PC will automatically save any changes you made to a file you are
editing, if you stop touching the keyboard for 10 minutes.
AUTOSAVEON Turn on auto save.
AUTOSAVEOFF Stop auto save.
AUTOSAVE-MINUTES Value of minutes to wait before saving.
Default is 10.
Screen display output can be switched between DOS and Direct Video output
for all screen text display.
FAST Direct video screen write for all displayed text.
SLOW Use DOS for all screen display.
F-PC defaults to automatically entering the editor when an error is
encountered during a file load. You can control this with the following
words.
AUTOEDITON Automatically enter editor on load error.
AUTOEDITOFF Don't enter editor on load error.
When an error occurs, the base for number conversions will be change back
to DECIMAL. This feature can be turn off so that the base is not affect
by errors.
DECIMALBASE Change to DECIMAL after an error.
HEXBASE Change to HEX after an error.
NOBASE Do not change base on error.
DEFBASE A value to restore base. 0 for NOBASE, 10 for
DECIMAL and 16 for HEXBASE. User can choose his
default base here.
If you are using a CGA (Color Graphics Adapter) type of video display
board, you will probably want to use BLANKON to reduce the amount of snow
or sparkle on your screen. This word causes the screen to be blanked
while text is being written to the display to reduce this effect. These
words have no effect on monochrome display adapters. Use BLANKOFF for an
EGA or VGA adapter.
BLANKON Enable screen blanking during text output.
BLANKOFF Disable screen blanking during text output.
Most green or amber monochrome monitors display light characters on a
dark background. If you have a color monitor or true white on black
monitor you may want to reverse foreground and background, giving a page
white look with dark characters on a white background. I have found this
to be more comfortable for my own use. You might also try the
BLACK-ON-WHITE mode with an Liquid Crystal or Florescent display.
WHITE-ON-BLACK Normal, light chars on dark background.
BLACK-ON-WHITE Invert the screen to dark on light.
With a color monitor, F-PC can display different classes of words in
different color. It is a very interesting demonstration to impress
novice programmers when executing WORDS, SEE, or DBG. It is probably not
very useful in normal programming because you cannot see very well words
in blue and light grey.
COLORIZEON Turn on colors in word list.
COLORIZOFF Go back to work
The number of screen F-PC will save on its screen stack if adjustable
within the range 1 to 14. SVSIZE bytes (~4000) are allocated for each
screen stacked. F-PC needs SVMAX to be at least three (3) for all of the
existing utilities to function properly.
SVMAX is a "VALUE" that can be changed with "=:". You will only need to
do this if you write a program that needs to stack screens more than the
default number of screen deep.
5 =: SVMAX \ increase number of buffers to 5
FSAVE F <enter> \ resave the system
BYE \ leave after changing and saving
F <enter> \ now the screen stack is 5 deep.
Your preferences can be edited into the configuration file F-PC.CFG.
This file is executed by F- PC immediately after it is loaded into
memory. Only a few of the preferences were included into the
configuration file during the installation/configuration process, and
most preferences were set to default choices. In the hypertext root
screen, a link item 'Preferences' is available for you to see all the
possible choices on-line.
9.5. TASK CHAINING
Tom Zimmer developed a very powerful technique by which more functions
can be added to a word as the needs grow. He called it background task
chaining. The idea is to use a DEFERred word as a basis. Some time
later this deferred word is resolved to do one task. We can add some
more tasks to this word by defining a new word and compiling the contents
of the deferred word into the new word with other functions. The
deferred word is then re-vectored to the new definition. When the
deferred word is executed, new functions are added to the old task. This
task chain can thus be extended to your heart's desire. The words
involved in task chaining are:
DEFER <name>
to define a deferred word whose function can be changed by re-vectoring,
and
DEFERS <name>
an immediate compiler word which compiles the contents of the next
deferred word in a colon definition. It allows many functions to be
added to the deferred word.
In F-PC, KEY is a user deferred word. We have to use DEFERS to extend
its function. BGSTUFF is a regular deferred word to extend functions like
the status line display. BYESTUFF is used to extend the cleaning up task
before F-PC exits to DOS. Let's use BGSTUFF as an example:
DEFER BGSTUFF
' NOOP IS BGSTUFF
: (KEY?)
DEFERS BGSTUFF
{ the words to do (KEY?) }
;
' (KEY?) IS BGSTUFF \ BGSTUFF = (KEY?)
: TIME
DEFERS BGSTUFF
#OUT @ #LINE @ \ save cursor position
64 0 AT .TIME \ print time at upper-right corner
AT \ restore cursor
;
' TIME IS BGSTUFF \ BGSTUFF = (KEY?) + .TIME
This technique allows you to dynamically change the behavior of a
deferred word while keeping most of its old functionality. As the system
grows, it is easier to add new functions to an existing word than to
define new words and mess up the existing environment.
9.6. CONTROL STRUCTURE ENHANCEMENTS
Bill Muench contributed a modified set of control structures. The
changes are very very minor, but result in a significant increase in
versatility. The change is effectively to move a 2SWAP from the
beginning of REPEAT and put it at the end of UNTIL. Some additional
words have also been added to take advantage of the increased
versatility. The changes have been added to the system, the meta
compiler, and the assembler.
Some possible combinations of the structures are shown in the following
cases. However, the possible combinations are only limited by your
imagination.
WHILE can be used to exit a DO...LOOP conditionally. The WHILE structure
can be nested.
DO ...
WHILE ...
WHILE ...
LOOP ...
ELSE UNDO ... \ drop or use index and limit
THEN ...
ELSE UNDO ... \ drop or use index and limit
THEN
A normal BEGIN..WHILE..REPEAT loop behaves like it always did:
BEGIN ...
WHILE ... \ normal structure
REPEAT
CONTINUE allows a conditional branch back to BEGIN:
BEGIN ...
IF ...
CONTINUE ... \ now branch back to begin
UNTIL \ otherwise, conditionally branch
WHILE can also leave a BEGIN..UNTIL loop conditionally.
BEGIN ...
WHILE ... \ multiple exit tests
UNTIL ...
ELSE ... \ and possibly different action
THEN
WHILE can also be nested in a BEGIN..UNTIL loop.
BEGIN ...
WHILE ... \ multiple exit tests
WHILE ... \ multiple exit tests
UNTIL ...
ELSE .. \ and possibly different action
THEN ...
ELSE ... \ and possibly different action
THEN
AFT..THEN structure can be nested inside BEGIN..WHILE..REPEAT loop. The
clause inside AFT..THEN is executed only once in the first looping.
BEGIN ...
AFT ... \ executed only once
THEN .. \ ignored afterwards
WHILE ...
REPEAT
The FOR...NEXT structure was proposed by Chuck Moore in the cmForth for
the Novix NC4000 Forth chip. FOR takes a count from the data stack and
pushes it onto the return stack. NEXT decrements the count on the return
stack. If the count becomes zero after being decremented, the loop is
terminated; otherwise, the loop is repeated.
The FOR...NEXT loop can also use WHILE to exit conditionally:
FOR ...
WHILE ... \ in effect an immediate ?leave
NEXT ...
ELSE ... R> ( DROP ) \ drop or use the loop index
THEN
AFT..THEN structure can also be nested in a FOR..NEXT loop.
FOR ...
AFT ... \ this is only executed the first
\ time through the loop
THEN ... \ this is executed every time
NEXT
Another way to exclude the n=0 case and also have the loop execute n
times, but is longer and slower specifically on a FORTH machine like the
NC4000 or Harris RTX.
( n ) ?DUP IF 1- FOR ... NEXT ... THEN
BREAK allows the construction of a case structure in a colon definition:
... IF ... BREAK \ case like structure
... IF ... BREAK \ break compiles an exit
... IF ... EXIT THEN \ same as break
9.7. HEADLESS WORDS
This is a neat utility from George T. Hawkins to allow the extraction and
removal of the unwanted heads in the Forth system and any application you
may write in F-PC.
Any words to be later beheaded are identified with a "HEADERLESS"
keyword. This is followed by the colon definitions or code words
themselves. You re-establish standard words (i.e., words with headers)
with the keyword "HEADERS".
When you have finished your use/referencing of headerless words, you then
use the keyword: "BEHEAD". This will completely remove the definition of
any headerless words from the directory.
Once headerless words are BEHEADed they are lost forever; i.e., their
code and list space is not lost - but they are unknown so far as the
dictionary is concerned. Note that you cannot ever reference a
HEADERLESS word once it is BEHEADed. So the logic to using HEADERLESS
words is as follows:
ONLY FORTH ALSO EDITOR ALSO HIDDEN \ set up search order as needed
HEADERLESS
... \ put headerless words here
HEADERS
... \ put words which reference
\ the previous group of
\ headerless words here
EDITOR DEFINITIONS \ switch to EDITOR vocabulary
\ but don't change order.
\ repeat above sequence of:
HEADERLESS \ Turn off heads in editor vocabulary
... <words> ...
HEADERS \ Turn heads back on
... <words> ...
HIDDEN DEFINITIONS \ switch to HIDDEN vocabulary but don't
\ change order.
\ as desired
BEHEAD
Although the use of headerless words can save you head space, their main
advantage is in the software engineering they provide. That is, the
definitions/names are *completely lost* not just stashed away in some
obscure vocabulary. (If you attempt to "see" or "debug" headerless words
through regular words you get a garbage ID.)
In general you should set up your {HEADERLESS/HEADERS}/ BEHEAD
definitions as described above, but precede it with a single "HWORDS-".
HWORDS- will cause HEADERLESS, HEADERS, and BEHEAD to be treated as
noops. Once you've finished debugging and are ready to go to production,
then change "HWORDS-" to "HWORDS+". This will give the HEADERLESS,
HEADERS, and BEHEAD words their standard meaning. If you ever need to
debug the code again, and want to see the names, then change HWORDS+ to
HWORDS-.
As can be seen in the above example, you should setup your vocabulary
search order prior to starting a sequence of definitions in which some
words will be headerless. After setting the search order, you can still
select different vocabularies in which you place definitions, but you
MUST NOT change the search order, that is you MUST NOT use "ONLY" or
"ALSO". Also the current vocabulary should not be changed while in
HEADERLESS mode.
9.8. SAVE AND RESTORE
At times one needs to change various global attributes of the Forth
system while preserving their value to be later restored. An example of
this might be changing CAPS to ON, while saving its current value to
restore later. Here is a typical code segment to save CAPS, turn it on,
and restore it at later in a definition:
: DEF1 ( --- )
CAPS @ >R CAPS ON \ Save CAPS and turn ON
...
use SEARCH for something ...
...
R> CAPS ! \ restore CAPS
;
While this is an acceptable way to save and restore a variable, it is
difficult to read, and not particularly efficient in terms of
performance. A new mechanism has been introduced which enhances
readability, and improves performance at the same time. Here is an
example of SAVE!> and RESTORE>:
: DEF1 ( --- )
TRUE SAVE!> CAPS \ save and set CAPS
...
use SEARCH for something ...
...
RESTORE> CAPS \ restore CAPS
;
These words allow a VARIABLE or VALUE to be saved for later, and set to a
new value for temporary use. Another word included in the set allows
saving a VARIABLE or VALUE without changing it, for later restoration:
: DEF1 ( --- )
SAVE> CAPS \ save CAPS
...
do something that may change CAPS...
...
RESTORE> CAPS \ restore CAPS
;
The only problem with these words is they cannot be use with user
variables, as they are fairly dumb and fast. They simply work with the
contents of the body of the definition following.
9.9 LINE EDITOR
F-PC provides a very nice general purpose line editor for use in your
application programs. It allows you to request a line of input from the
user, while allows him to edit the text before pressing <return> to send
it to the program. The word to invoke it is LINEEDITOR. Its usage is as
follows:
20 8 MYBUF 22 LINEEDITOR ( -- f )
In this example, the text buffer will start at column 20 of row 8.
Editing will be performed on the counted string in MYBUF, and the maximum
length allowed is 22 characters. The line editor is terminated by either
<return> or ESC key. If the ESC key is pressed than a false boolean flag
is returned; otherwise, a true flag is returned. A mouse can be used to
position the cursor within the edit line.
If the editing is completed with <return>, then the edit string is placed
back into MYBUF. If the editing is terminated with ESC, then MYBUF will
contain the original string unmodified by any edit operations performed
during the editing session.
During editing, you can use the Right arrow, Left arrow, Home, End, and
Delete keys to position the cursor to edit the string.