Fleet Forth design considerations

[JimBoyd]

I may have given Fleet Forth's EXPECT nonstandard behavior.
The Forth-83 Standard states the following concerning EXPECT .

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          9.5.2     EXPECT

          Control characters may be processed to allow system dependent
          editing of the characters prior to receipt.  Therefore, a
          Standard Program may not anticipated that control characters can
          be received.

It doesn't seem to say anything about intercepting function keys; however, I thought such a capability would be useful. In Fleet Forth, EXPECT is a DEFERred word. It is normally set to (EXPECT) .
The high level portion of (EXPECT) reads the keyboard and echoes the characters back to the screen. If a carriage return is detected in the keyboard buffer, it is not read. Control flow passes to the low level portion of (EXPECT) which uses the Commodore 64's screen editor, kernal routine CHRIN , $FFCF.
The word which echoes keys to the screen is DEMIT . It is a primitive which uses the same C64 kernal routines as (EMIT) . As the leading 'D' in the name implies, it is normally used to send a character to a disk drive, but can also send a character to the screen. The difference with (EMIT) , the vector for EMIT , is DEMIT does not update the variables CHARS and LINES . These variables are used for 'print formatting'. They keep track of the number of characters emitted since the last carriage return or page and the number of lines since the last page.
DEMIT was replaced with the following:

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         7 OVER #133 - U<   \ is this not a function key?
         IF                 \ if it is not
            DEMIT           \ echo to the screen as usual
         ELSE               \ else
            #63 +  4 /MOD SWAP 2* +   \ convert PETSCII code
            " F0" TUCK 2+ C!          \ insert digit character into string
            CONTEXT @ (FIND)          \ and search CONTEXT vocabulary
            IF  DUP EXECUTE  THEN     \ if found, execute
            DROP                        
         THEN

The search of the CONTEXT vocabulary will include the parent vocabularies.

The Commodore 64's function keys are a little different. There are only four actual function keys: F1, F3, F5 and F7. F2 is obtained with shift-F1, F4 with shift-F3 and so on.
The PETSCII codes are as follows:

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F1  133
F3  134
F5  135
F7  136
F2  137
F4  138
F6  139
F8  140

in function key order:

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F1  133
F2  137
F3  134
F4  138
F5  135
F6  139
F7  136
F8  140

This line:

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            #63 +  4 /MOD SWAP 2* +   \ convert PETSCII code

performs the following conversion:

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133 => 49
137 => 50
134 => 51
138 => 52
135 => 53
139 => 54
136 => 55
140 => 56

An eight byte look-up table could have been used, but this was smaller.

If function key F1 is pressed and there is no word by that name, it's the same as if the function key was not pressed. If the name exists, it is executed.

I've notice the function key names could be confused with hexadecimal numbers. I've gotten too used to using $F1 for a hexadecimal number. I could change this line:

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   " F0" TUCK 2+ C!          \ insert digit character into string

to this:

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   " FKEY0" TUCK 5 + C!          \ insert digit character into string

Or something similar.

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   " FKEY0" [ HERE 1- ] SWAP LITERAL C! \ insert digit character into string

or even

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   [ HERE 2+ ] $FFFF    \ compile a literal
   C!
   " FKEY0"  [ HERE 1- SWAP! ]  \ patch literal with address of 
                                \ last character in string.

To use function key F1 with this change there would need to be a word with the name FKEY1 .

[GARTHWILSON]

I've only used code page 437, which clearly the C64 doesn't use.  I haven't thought about how I'd use the C64 character set (including function keys), but CP437 is sure nice for the special characters, drawing boxes, and the Greek letters we use all the time in engineering (since that's what I'm always using Forth for).  The Epson dot-matrix impact printers, which Epson is still making about nine models of, use the same character set, so I use it with the workbench computer too, although they don't display correctly in its small LCD unless I make custom characters in the LCD, which I've done before but is kind of a lot of overhead.  My exception to the 437-only use is my HP-71B hand-held computer which defaults to the ROMAN8 set which is kind of similar but has different byte values for the special characters; but after the HP Thinkjet printer I was using with it went down and I started using the Epson printer, I loaded the CP437 character set into the HP71 computer so things would display correctly in its LCD.  Here are a couple of examples of my uses of the box-drawing characters:

(although that last one was for a PIC16 project, not 6502).  CP437 also lets me have Forth word names like ±½°C or 10KΩ or put Φ2 in the comments.

[JimBoyd]

GARTHWILSON wrote:

I've only used code page 437, which clearly the C64 doesn't use.  I haven't thought about how I'd use the C64 character set (including function keys), but CP437 is sure nice for the special characters, drawing boxes, and the Greek letters we use all the time in engineering (since that's what I'm always using Forth for).

I remember code page 437. I haven't seen it since my days of using DOS.
The visual appearance of text windows can be created on the C64 using reverse video. Ctrl-R on the C64 selects reverse video and Ctrl-0 ( control zero) selects normal video.
Here is were I selected a black background and white text and played around on the screen by selecting and deselecting reverse video. I typed the text with spaces to achieve the look of windows.

I normally use reverse video on the C64 to highlight important information.

Fleet Forth has the words RON to switch reverse video on and ROFF to switch to normal video. A carriage return also switches reverse video off.

[JimBoyd]

I've removed the words <LIST <L LIST> L> and their editor words 0[ through F[ and 0] through F] because they were unsatisfactory.
I also mentioned a solution which seems satisfactory.
A new LIST word which use an editing window VALUE for a displacement to the right, EW , and a corresponding set of editing words 0[ through F[ which also use EW.

I would like to mention that the word // is Fleet Forth's word to comment to the end of a line. It will also skip the rest of the line when used at the command line or in an EVALUATEed string.
The comments in the listing which have a backslash were added to this post for clarity.

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0 VALUE EW
: LISTW  ( SCR -- )
   EW #28 UMIN (IS) EW              \ be certain EW is from 0 - 28
                                    \ inclusive.
   PAGE  EDITOR  R# OFF DUP SCR !   \ clear the screen, select EDITOR 
                                    \ vocabulary & misc. housekeeping.
   ." SCR# " DUP U. SPACE BLK> . .  \ show screen number.
                                    \ BLK> breaks that number down
                                    \ to a screen number relative to 
                                    \ the drive it is from and the
                                    \ drive number.
   10 SPACES EW .                   \ show displacement to the right
   #16 0  CR
   DO
      I 0 H.R ." [ "
      I LINE  EW /STRING #36 UMIN   \ only show 36 columns
      QTYPE CR                      \ type in 'quote mode'
      DONE? ?LEAVE
   LOOP ;

EDITOR DEFINITIONS
: XED2  ( N -- )
   CREATE  ( N -- )
      C,
   DOES>   ( -- )
      C@ LINE  0 TEXT PAD 1+  -ROT
      EW #28 UMIN /STRING  #36 UMIN
      MOVE UPDATE
      3 RC !  QUIT -;
: LW  ( -- )
   SCR @ LISTW ;


 0 XED2 0[    1 XED2 1[    2 XED2 2[
 3 XED2 3[    4 XED2 4[    5 XED2 5[
 6 XED2 6[    7 XED2 7[    8 XED2 8[
 9 XED2 9[   $A XED2 A[   $B XED2 B[
$C XED2 C[   $D XED2 D[   $E XED2 E[
$F XED2 F[
FORTH DEFINITIONS

LINE takes an number from 0 to 15 and returns the address, in the block buffer, of that line for the current screen, the one which has its block number stored in SCR .
0 TEXT reads the rest of the line in the text input buffer and stores it at PAD . After -ROT the stack has the following three parameters on top.
The address of the text to copy.
The address of the line of the current screen for this child word.
A count of 64.
The line

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      EW #28 UMIN /STRING  #36 UMIN

increments the destination address by EW bytes and clips the length of the transfer to 36 bytes, the length of the edit window.
The string is MOVEd to the block buffer and the buffer updated.
Fleet Forth's EXPECT starts at the beginning of a line on the view screen and will perform a carriage return if necessary. Setting the variable RC to 3 will cause EXPECT to move the cursor right by three.

That reversed video colon after 2[ is a snapshot of the blinking cursor. It was placed there after pressing the return key anywhere on the previous line.

Fleet Forth's EXPECT was modified to test for function keys. The function key words can be executed without the need to scroll down from the text being edited.

Some sample function key words I was trying. This is how the screen appears when listing with LISTW and EW is zero. The listings are sent to a printer, or in my case, a print.dump file.

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\       ----------------------- actual screen number 
\      |    ------------------- drive number
\      |   |   ---------------- screen number relative to drive
\      v   v   v
SCR# 4719  2 623           0 -- editor window displacement
0[ // EDITOR FKEYS                     
1[ EDITOR DEFINITIONS                  
2[ : F1KEY  ( -- )               // MOV
3[    0 TO EW   [ HERE >A ]            
4[    XY 1 MAX 16 MIN LW AT-XY ;       
5[ : F3KEY  ( -- )               // MOV
6[    EW 7 - 0 MAX TO EW               
7[    BRANCH [ A@ , ] -;               
8[ : F5KEY  ( -- )               // MOV
9[    EW 7 + #28 MIN TO EW             
A[    BRANCH [ A@ , ] -;               
B[ : F7KEY  ( -- )  #28 TO EW    // MOV
C[    BRANCH [ A> , ] -;               
D[ : F2KEY  ( -- )               // MOV
E[    0 18 AT-XY ;                     
F[ FORTH DEFINITIONS                   

And when EW is 14.

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SCR# 4719  2 623           14 
0[ S                                   
1[ IONS                                
2[ )               // MOVE EDIT WINDOW 
3[  HERE >A ]                          
4[  MIN LW AT-XY ;                     
5[ )               // MOVE WINDOW LEFT 
6[ X TO EW                             
7[  , ] -;                             
8[ )               // MOVE WINDOW RIGHT
9[ MIN TO EW                           
A[  , ] -;                             
B[ )  #28 TO EW    // MOVE EDIT WINDOW 
C[  , ] -;                             
D[ )               // MOVE CURSOR TO BE
E[ ;                                   
F[ ONS                                 

When listing with LIST .

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SCR# 4719  2 623 
0: // EDITOR FKEYS
1: EDITOR DEFINITIONS
2: : F1KEY  ( -- )               // MOVE EDIT WINDOW TO BEGINNING
3:    0 TO EW   [ HERE >A ]
4:    XY 1 MAX 16 MIN LW AT-XY ;
5: : F3KEY  ( -- )               // MOVE WINDOW LEFT 7 COLUMNS
6:    EW 7 - 0 MAX TO EW
7:    BRANCH [ A@ , ] -;
8: : F5KEY  ( -- )               // MOVE WINDOW RIGHT 7 COLUMNS
9:    EW 7 + #28 MIN TO EW
A:    BRANCH [ A@ , ] -;
B: : F7KEY  ( -- )  #28 TO EW    // MOVE EDIT WINDOW TO END
C:    BRANCH [ A> , ] -;
D: : F2KEY  ( -- )               // MOVE CURSOR TO BELOW EDIT AREA
E:    0 18 AT-XY ;
F: FORTH DEFINITIONS

And with what I normally use to list screens to a print.dump file, PLIST , plain list.

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SCR# 623 
// EDITOR FKEYS
EDITOR DEFINITIONS
: F1KEY  ( -- )               // MOVE EDIT WINDOW TO BEGINNING
   0 TO EW   [ HERE >A ]
   XY 1 MAX 16 MIN LW AT-XY ;
: F3KEY  ( -- )               // MOVE WINDOW LEFT 7 COLUMNS
   EW 7 - 0 MAX TO EW
   BRANCH [ A@ , ] -;
: F5KEY  ( -- )               // MOVE WINDOW RIGHT 7 COLUMNS
   EW 7 + #28 MIN TO EW
   BRANCH [ A@ , ] -;
: F7KEY  ( -- )  #28 TO EW    // MOVE EDIT WINDOW TO END
   BRANCH [ A> , ] -;
: F2KEY  ( -- )               // MOVE CURSOR TO BELOW EDIT AREA
   0 18 AT-XY ;
FORTH DEFINITIONS

Although with the last two, there will be a line wrap on the Commodore 64's video screen.

F1KEY moves the editing window all the way to the left by setting EW to zero. XY returns the X (from left to right) and Y (from top to bottom) coordinates of the text cursor. AT-XY sets the coordinates, which places the cursor at those coordinates.
Suppose I wish to add a comment for the definition of F1KEY . While in the editor vocabulary, I press the F1 key and scroll up to the line with the name F1KEY . I press the F7 key and the listing is updated to show the last 36 columns of the screen, but the cursor is on the same line as it was before pressing the F7 key. I can now add a comment knowing it is on the correct line.

[JimBoyd]

In the Fleet Forth kernel there are eighteen headerless words. Words like the one formerly named TRAVERSE or some of the words used by the sector read/write word, SR/W . These headerless words have no use outside the kernel, which is why they are headerless. There is another group of words which are not directly used outside the kernel, the run-time words of other words.
Here are some of the compiling words and associated run-time words

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DO     (DO)
?DO    (?DO)
LOOP   (LOOP)
+LOOP  (+LOOP)
"      (")
."     (.")
ABORT" (ABORT")
IS     (IS)
TO     (IS)

I may change the names of some of these run-time words but these words will not be made headerless. The few dozen bytes saved would not justify the increased complexity in the design of the decompiler, SEE .

[JimBoyd]

I've mentioned Fleet Forth's TRACE and the ability to change what information is displayed by setting the DEFERred word .STEP to a step display word more appropriate for the trace.

Here is yet another example of how TRACE's step display can be customized. I recently made a modification to Fleet Forth's metacompiler. One of the words copies a string to HERE and modifies it, if necessary. The reason PAD isn't used is because Fleet Forth has the word >HERE in the kernel.
I wanted to see what was happening at HERE when tracing that word.

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: .STMETA 
   (.ST1) CR HERE $10 DUMP ;
' .STMETA IS .STEP

(.ST1) is the default step display word. .STMETA calls (.ST1) for the usual display for the current step and then dumps the first sixteen bytes at HERE .

[JimBoyd]

JimBoyd wrote:

I may have given Fleet Forth's EXPECT nonstandard behavior.
The Forth-83 Standard states the following concerning EXPECT .

Code: Select all

          9.5.2     EXPECT

          Control characters may be processed to allow system dependent
          editing of the characters prior to receipt.  Therefore, a
          Standard Program may not anticipated that control characters can
          be received.

It doesn't seem to say anything about intercepting function keys; however, I thought such a capability would be useful.

I have found nothing in the Forth-83 Standard for or against this extra functionality in EXPECT .
The closest I've seen is this excerpt for the Forth 2012 Standard's ACCEPT .

forth-standard.org wrote:

It is recommended that all non-graphic characters be reserved for editing or control functions and not be stored in the input string.

Fleet Forth is a Forth-83 Standard Forth for the most part; however, when there is something not covered in the Forth-83 Standard I will check the other standards for the least objectionable approach to minimizing divergent behavior in my Forth when adding new functionality to the kernel. One such example is renaming Fleet Forth's UNDO to UNLOOP .
ACCEPT is the Forth 2012 Standard version of EXPECT with slightly different behavior. As such, where the Forth-83 Standard is quiet concerning the use of function keys in EXPECT , I'll accept the Forth 2012 Standard's recommendations for ACCEPT . The relevant phrase describing ACCEPT is "or control functions" which would indicate that it is acceptable for ACCEPT , and therefore EXPECT , to intercept function keys and use them for control purposes.

[JimBoyd]

FSAVE is Fleet Forth's word to save the Forth system as a Commodore program file. FSAVE would prompt for a file name and use EXPECT to read in the file name to use; however, I have found that I would occasionally type a file name right after FSAVE when I already had a file name in mind and I was in a hurry. This made me wonder if having the file name inline was a more natural way to do things. The file name used by FSAVE now follows it in the text stream. FSAVE uses 0 WORD so file names with spaces can be used.

[BruceRMcF]

JimBoyd wrote:

JimBoyd wrote:

I may have given Fleet Forth's EXPECT nonstandard behavior.
The Forth-83 Standard states the following concerning EXPECT .

Code: Select all

          9.5.2     EXPECT

          Control characters may be processed to allow system dependent
          editing of the characters prior to receipt.  Therefore, a
          Standard Program may not anticipated that control characters can
          be received.

It doesn't seem to say anything about intercepting function keys; however, I thought such a capability would be useful.

I have found nothing in the Forth-83 Standard for or against this extra functionality in EXPECT .
The closest I've seen is this excerpt for the Forth 2012 Standard's ACCEPT .

forth-standard.org wrote:

It is recommended that all non-graphic characters be reserved for editing or control functions and not be stored in the input string.

Forth-94 slightly generalized the Forth-83 EXPECT specification by specifying that author of Forth-94 source could not depend on being able to receive non-graphical characters, which is more explicit about setting aside what is returned by a function key unless it returns one or more graphical characters.

However, function keys themselves do not come into scope until Forth-2012, which is also when "a source cannot depend on non-graphical characters being stored" was strengthened to "it is recommended that a system refrain from storing non-graphical characters".

Quote:

Fleet Forth is a Forth-83 Standard Forth for the most part; however, when there is something not covered in the Forth-83 Standard I will check the other standards for the least objectionable approach to minimizing divergent behavior in my Forth when adding new functionality to the kernel. One such example is renaming Fleet Forth's UNDO to UNLOOP .
ACCEPT is the Forth 2012 Standard version of EXPECT with slightly different behavior. As such, where the Forth-83 Standard is quiet concerning the use of function keys in EXPECT , I'll accept the Forth 2012 Standard's recommendations for ACCEPT . The relevant phrase describing ACCEPT is "or control functions" which would indicate that it is acceptable for ACCEPT , and therefore EXPECT , to intercept function keys and use them for control purposes.

I'd say it is good for sanity if EXPECT is implemented in a way that allows a set of Forth-94 / Forth-2012 portability screens to define ACCEPT as "EXPECT SPAN @".

[JimBoyd]

One feature of VICE I have used in moderation is the ability to paste text into the simulator. Fleet Forth behaves as though the text is typed in. This does introduce a problem. When loading source from screens on blocks or even from a Commodore sequential file, an ABORT stops the load and returns control to Forth's QUIT loop. When text is pasted into the simulator the QUIT loop still has control. an ABORT stops interpreting text which has already been EXPECTed, or ACCEPTed; however, the simulator continues to fill the keyboard buffer until all pasted text has been inserted into the keyboard buffer. The behavior is exactly as if a programmer typing in source ignores errors and continues typing.
Fleet Forth's ABORT , which is called by ABORT" , is extensible.

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: ABORT  ( -- )
   SINGLE ERR SP! AP! QUIT -;

SINGLE switches off multitasking.
SP! and AP! clear the data and auxiliary stacks.
ERR is a deferred word which normally executes NOOP a Forth no-op.
I set ERR to the word PURGE when I wish to paste Forth source from a Linux text file.

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: PURGE           // EMPTY KEYBOARD
   BEGIN          // BUFFER
      BEGIN
         KEY?     // ANY KEYSTROKES?
      WHILE
         KEY DROP
      REPEAT
      1 JIFFIES   // WAIT 1/60 SEC
      KEY? 0=     // BUFFER EMPTY?
   UNTIL ;

KEY? is an AnsiForth word which returns TRUE if a character is available.
The 1 jiffy delay is to give VICE time to refill the keyboard buffer. The inner loop empties the keyboard buffer fast enough that without the delay, PURGE returns before VICE is finished adding pasted text to the buffer.

[JimBoyd]

I should have mentioned that keyboard input in Fleet Forth causes the cursor to blink while waiting for input. When PURGE is used to purge the pasted text after an error occurs, I know it is done when the cursor resumes blinking at a steady rate.

[JimBoyd]

JimBoyd wrote:

In the Fleet Forth kernel there are eighteen headerless words. Words like the one formerly named TRAVERSE or some of the words used by the sector read/write word, SR/W . These headerless words have no use outside the kernel, which is why they are headerless. There is another group of words which are not directly used outside the kernel, the run-time words of other words.

Some of the run-time words now have the same name as the associated compiling word.

Code: Select all

DO     DO
?DO    ?DO
LOOP   LOOP
+LOOP  +LOOP
"      "
."     ."
ABORT" ABORT"

(IS) is still the run-time for IS and TO .
The run-time words are defined before the word FORTH-83 and the compiling words are defined after. This made updating the source for SEE easier.
To find the run-time words, the FORTH vocabulary is set as both the CONTEXT and CURRENT vocabularies. Create a false vocabulary on the auxiliary stack with FORTH-83 as the latest word with the following:

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0 ' FORTH-83 >LINK 2>A

and make it the CONTEXT vocabulary.

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AP0 @ @ CONTEXT !

The false vocabulary, the portion of the FORTH vocabulary from FORTH-83 to the beginning is searched. If the sought word is not found in this false CONTEXT vocabulary, the CURRENT vocabulary, which is all of the FORTH vocabulary, is searched.

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 OK
SEE DO 
DO IMMEDIATE
 2DA2 20A6 COMPILE
 2DA4  912 DO
 2DA6 2CAE >MARK
 2DA8 12E6 2+
 2DAA 2CC2 <MARK
 2DAC 12E6 2+
 2DAE  9A8 EXIT
E 
 OK
0 ' FORTH-83 >LINK 2>A AP0 @ @ CONTEXT !  OK
SEE DO 
DO
  914         INY
  915   FB )Y LDA IP
  917         PHA
  918         DEY
  919   FB )Y LDA IP
  91B         PHA
  91C         CLC
  91D    3 ,X LDA
  91F   80  # ADC
  921         PHA
  922    3 ,X STA
  924    2 ,X LDA
  926         PHA
  927         SEC
  928    0 ,X LDA
  92A    2 ,X SBC
  92C         TAY
  92D    1 ,X LDA
  92F    3 ,X SBC
  931         PHA
  932         TYA
  933         PHA
  934         INX
  935         INX
  936         INX
  937         INX
  938  8ED ^^ BPL ' ?BRANCH >BODY 8 +
  93A  839    JMP ' ! >BODY 14 +
29 
 OK
CONSOLE 

[Edit: Corrected explanation of the vocabulary search.]

[JimBoyd]

JimBoyd wrote:

Leo Brodie introduced the word \S in his book Thinking Forth. \S stops the rest of a screen from loading.

The Forth-83 Standard has the uncontrolled reference word ;S which does the same thing.

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          ;S           --                            Interpret only"semi-s"
               Stop interpretation of a block.

[JimBoyd]

JimBoyd wrote:

I have another word to parse strings. It is used by the following words.

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(
.(
"
."
ABORT"

I call this word CHAR ; however, the Ansi Forth standard has a word by that name which, along with [CHAR] , does what ASCII does in a Forth-83 system so I may rename Fleet Forth's CHAR . It works a lot like the Ansi Forth word PARSE in that it does not skip initial occurrences of the delimiter and it returns an address and count. It is different in that it will ABORT if the delimiter is not found.

I do not wish to change this word's name to PARSE for two reasons. It does more than ANSI Forth's PARSE by aborting if the delimiter is not found and I do not think PARSE is a good name for extracting a string from a text stream. The word PARSE implies some kind of analysis, such as is performed by the parser of some language compilers.
I think the name PLUCK would be a good one. PLUCK a string from the text stream.

[BruceRMcF]

JimBoyd wrote:

... The word PARSE implies some kind of analysis, such as is performed by the parser of some language compilers. ...

The dictionary definition I find of parsing has it as a synonym of syntatic analysis and does indeed refer to analyzing a string of symbols, but if the underlying syntax is as simple as Forth ... tokens and separators with the tokens referring to tags if they are present in a dictionary, if not referring to numbers under the current base, ... then the location and the length of the token is much of the syntactic analysis that is required.

Forth 200x PARSE-NAME then is an action to implement the syntactic analysis required for the default syntax, working well with whitespace by skipping leading delimiters, and Forth94 PARSE is an action to support additional syntax to terminate a substring in the string of symbols by defining an explicit terminator, while allowing for empty substrings by not skipping leading delimiters.

In any event, neither Forth94 PARSE nor Forth200x PARSE-NAME have an abort or error on delimiter not found, but both implicitly take the end of the input buffer as matching any parsing delimiter, so if there is an abort on the delimiter not found, perhaps it's best to not call it PARSE or PARSE-NAME to avoid confusion.

Quote:

... I think the name PLUCK would be a good one. PLUCK a string from the text stream.

Is that pluck as in chicken feathers or pluck as in a harp string?

Given that the Forth style syntax is just slicing up the input buffer into tokens, I like SLICE if you want to name it in terms of the action or TOKEN or STRING if you want to name it by the result it is going to give.