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DX-FORTH v4.30
2024-07-09 18:07:02 +02:00
DX-Forth for MS-DOS Extension Wordset Glossary
----------------------------------------------
The DX-Forth Extension Wordset is provided in addition to the FORTH-94
Standard words. Standard words that are implementation-specific, used
for reference or other purpose may also be described.
Attributes:
I Words that have the immediate flag set
A Words residing in the DX-Forth APPLICATION dictionary
S Words residing in the DX-Forth SYSTEM dictionary
94 Words defined in the Forth-94 Standard
83 Words defined in the Forth-83 Standard
79 Words defined in the Forth-79 Standard
FIG Words defined in the fig-Forth model
Stack notation:
Note: The following naming conventions for addresses are used to
maintain compatibility with the ANS-FORTH document. As DX-Forth does
not currently execute on architectures requiring address alignment,
all address types may be used interchangeably.
number type stack cells range
----- ---- ----------- -----
addr address 1 0..65535
a-addr aligned address 1 0..65535
c-addr character-aligned address 1 0..65535
f-addr float-aligned address 1 0..65535
p-addr CPU port address 1 0..65535
h-addr heads segment address 1 0..65535
true boolean true -1 1 -1
false boolean false 0 1 0
flag boolean true or false 1 -1 or 0
ior input/output result 1 0..255
n signed number 1 -32768..32767
+n positive number 1 0..32767
u unsigned number 1 0..65535
x unspecified number 1 -32768..65535
d signed double number 2 -2147483648..
2147483647
+d positive double number 2 0..2147483647
ud unsigned double number 2 0..4294697295
xd unspecified double number 2 -2147483648..
4294697295
r real number 2 +-5E-39..1E38
c character or byte 1 0..255
ccc any arbitrary blank-delimited character string or word name
parsed from the input stream
"ccc" same as for ccc; typically shown within a stack comment but
represents characters parsed from the input stream.
Contents
1. Disk File Interface
2. Screen Files
3. Tools
4. DOS Interface
5. Input/Output
6. Arithmetic and Stack
7. Conversion
8. Strings and Memory
9. Dictionary
10. Facility
11. Miscellaneous
12. Floating Point
13. Compiler Security
14. Control Flow
1. Disk File Interface
----------------------
Note: When a file function returns a non-zero ior then an error has
occurred. Refer to DXFORTH.TXT for a list of ior values and their
corresponding DOS error.
+EXT ( c-addr1 u1 c-addr2 u2 -- c-addr3 u3 ) A
Conditionally append the extension c-addr2 u2 to the filename
string c-addr1 u1 to produce a temporary string c-addr3 u3 in the
filename buffer. If addr1 u1 does not already contain an extension
(the '.' character is not present) then trailing blanks are removed
and c-addr2 u2 is appended. Formerly named +FILENAME .
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
See >FNAME
-EXT ( c-addr u1 -- c-addr u2 ) A
Delete any extension from the filename string c-addr u1. The
resulting string is c-addr u2. Formerly named -FILENAME .
-PATH ( c-addr u1 -- c-addr u2 ) A
Delete any path from the filename string c-addr u1. The resulting
string is c-addr u2.
>FNAME ( c-addr1 u -- c-addr2 ) A
String c-addr1 u is converted to a temporary null-terminated
counted string in the filename buffer. Leading and trailing blanks
are removed. c-addr2 is the address of the counted string and
c-addr2+1 is the address of the null-terminated string. A maximum
of two such filenames can exist in the filename buffer at one time.
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
DX-Forth functions that use >FNAME or the filename buffer include:
PATH +EXT OPEN-FILE CREATE-FILE DELETE-FILE RENAME-FILE FILE-STATUS
See LASTFILE
BIN ( fam1 -- fam2 ) A I 94
Modify the file access method fam1 to additionally select a binary
- i.e. not line oriented - file access method, giving access method
fam2. BIN is a no-operation in this implementation as all access
is binary.
See READ-LINE
CLOSE-FILE ( fid -- ior ) A 94
Close the disk file associated with file-handle fid. If the file
could not be closed, ior is non-zero.
Note: Under CP/M files are a multiple of 128 bytes. Partly
written records are padded with end-of-file character (1A hex).
CREATE-FILE ( c-addr u fam -- fid ior ) A 94
Create and open a disk file specified by the filename c-addr u
using file access method fam. Valid fam are R/W (read/write)
R/O (read-only) and W/O (write-only).
If a file with the same name already exists it will be erased.
The file-pointer is set to the start of the file. If the file
could not be created, ior is non-zero.
DELETE-FILE ( c-addr u -- ior ) A 94
Delete the disk file specified by the string c-addr u. If the
file could not be deleted, ior is non-zero.
Note: DELETE-FILE must not be performed on an open file.
FILE-POSITION ( fid -- ud ior ) A 94
Return the current position the file-pointer of the disk file
associated with the handle fid. If an error occurs ior is
non-zero and ud is undefined.
FILE-SIZE ( fid -- ud ior ) A 94
Return the current size in bytes of the disk file associated
with handle fid. If an error occurs ior is non-zero and ud is
undefined.
Note: Under CP/M files are a multiple of 128 bytes. Partly
written records are padded with end-of-file character (1A hex).
FILE-STATUS ( c-addr u -- x ior ) A 94
Return the status of the file identified by c-addr u. In DX-Forth
it is equivalent to MS-DOS function INT 21H AX=4300H.
FLUSH-FILE ( fid -- ior ) A 94
Flush any buffered data written to the disk file associated with
handle fid, updating size information in the directory if changed.
If an error occurs ior is non-zero.
OPEN-FILE ( c-addr u fam -- fid ior ) A 94
Open the existing disk file specified by the filename c-addr u
using file access method fam. Valid fam are R/W (read/write)
R/O (read-only) and W/O (write-only). If the file could not be
opened, ior is non-zero.
PATH ( u1 -- c-addr u2 ior ) A
Get the full directory path for disk drive u1. If an error occurs,
ior is non-zero. The returned string c-addr u2 includes the drive
letter and a trailing backslash. For the currently selected drive
u1 = 0, otherwise u1 = 1 for drive A, 2 for drive B etc.
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
See >FNAME
LREAD ( seg offs u1 fid -- u2 ior ) A
As for READ-FILE but uses the 8086 segment/offset as the
destination address.
LWRITE ( seg offs u fid -- ior ) A
As for WRITE-FILE but uses the 8086 segment/offset as the source
address.
READ-FILE ( c-addr u1 fid -- u2 ior ) A 94
Read u1 bytes from the disk file associated with the current file-
handle into memory starting at c-addr. If ior is zero, u2 is the
number of bytes received. If physical end-of-file is reached
before any bytes are read, u2 is zero.
Note: Under CP/M files are a multiple of 128 bytes. Partly
written records are padded with end-of-file character (1A hex).
READ-LINE ( c-addr u1 fid -- u2 flag ior ) A 94
Read a line of text from the disk file associated with file-handle
fid into memory starting at address c-addr. At most u1 characters
are read. If ior is zero and flag is true, u2 is the number
characters received not including the line terminator. If u2 = u1
then a line terminator was not yet received. If an end-of-file
character (1A hex) is read or the end of the file is reached
before any other character is read then flag is false. The line
terminator may be CRLF (CP/M and MS-DOS) or LF (UNIX).
REPOSITION-FILE ( ud fid -- ior ) A 94
Reposition the file-pointer of the disk file associated with the
file-handle fid to position ud. If the file is positioned outside
the file boundaries or an error occured, ior is non-zero. If
ud = 0 the file-pointer is positioned at the start of the file.
RENAME-FILE ( c-addr1 u1 c-addr2 u2 -- ior ) A 94
Rename the disk file specified by c-addr1 u1 to the new name
c-addr2 u2. If the file cannot be found or the new name already
exists then ior is non-zero. Any drive/user prefix attached to
the new name is ignored and is assumed to be the same as the old
name.
Note: RENAME-FILE must not be performed on an open file.
WRITE-FILE ( c-addr u fid -- ior ) A 94
Write u bytes from memory starting at c-addr to the disk file
associated with the current file-handle. If the disk was full
or an error occured, ior is non-zero.
WRITE-LINE ( c-addr u fid -- ior ) A 94
Write a line of text c-addr u followed by the CP/M line terminator
(CRLF) to the disk file associated with file-handle fid. If the
disk was full or an error occured, ior is non-zero.
2. Screen Files
---------------
In DX-Forth several source files may be open at any one time. The most
recently opened screen-file is termed "the current screen-file".
Screen/block numbers are valid only in the range 0 to 8191. Only one
block buffer is allocated in memory, thus BLOCK and BUFFER always return
the same physical address.
DX-Forth also supports text source-files. See the section 'Tools' for
details.
#SCREENS ( -- +n ) S
Return the number of screens (blocks) in the current screen-file.
?BLOCK ( -- ) S
If the contents of BLK is non-zero perform BLK @ BLOCK DROP .
B/BUF ( -- u ) S FIG
A VALUE returning the number of bytes per block buffer. Default
is 1024.
Note: Must be a multiple of 128 and a maximum of 1280.
C/L ( -- u ) S FIG
A VALUE returning the number of characters per line in a screen
block. Default is 64.
CLOSE ( -- ) S
Flush and close the current screen-file. No errors are reported
with this function.
CLOSE-ALL ( -- ) S
Perform CLOSE on all open source-files beginning with the current
screen-file. Any open text-files are also closed with this
function.
SCREEN? ( -- flag ) S
Return true if the current screen-file is open otherwise return
false. Formerly named FILE?
FILEBLOCKS ( +n -- ) S
Resize the current screen-file to +n blocks. If n is less than
the current size, the screen-file is truncated otherwise the file
is extended and the new blocks are filled with blanks.
FLOAD ( +n "filename[.SCR]" -- ) S
Save the current screen-file specification then open the specified
file and load block +n. At completion of the load, close the file
and restore the previous file. If the filename does not include
an extension then .SCR is assumed. Screen-files may be nested.
Equivalent to: DUP GETFILENAME LOADED
Note: Read-only files cannot be opened with this function.
GETFILENAME ( "filename" -- c-addr u ) S
Parse a filename string from the input stream returning c-addr u.
An error occurs if the string is empty.
LOADED ( +n1 +n2 c-addr u -- ) S
Save the current screen-file specification then open the
screen-file specified by c-addr u and load blocks +n1 thru +n2.
At completion close the file and restore the previous screen-file.
If the filename does not include an extension then .SCR is
assumed. Screen-files may be nested.
Note: Read-only files cannot be opened with this function.
See FLOAD
LOADFILE ( -- c-addr u ) S
Return a string containing the name of the current source-file.
If no source-file is open or the input source is the console,
c-addr u is ambiguous. Formerly named FNAME FILENAME .
See SCREEN? LASTFILE
OPEN ( c-addr u fam -- ior ) S
Open the specified disk file according to file access method fam
as the current screen-file. If an error occurs, ior is non-zero.
If the filename does not include an extension then .SCR is
assumed.
Note: The programmer is responsible for closing or maintaining the
previous screen-file.
See SWAP-FILE CLOSE CLOSE-ALL USING
SWAP-FILE ( -- ) S
Switch the current and 'swap' screen-files. SCR is preserved
across swaps.
Note: SWAP-FILE causes the current block buffer to be unassigned.
The contents of the buffer, however, are not affected.
See FYI
USING ( "filename[.SCR]" -- ) S
Close the current screen-file. Open or conditionally create the
specified disk file for read/write as the current screen-file. If
the filename does not include an extension then .SCR is assumed.
If the file cannot be opened/created then ABORT is performed.
SCR is set to 0.
Note: Read-only files cannot be opened with this function.
The programmer is responsible for closing or maintaining the
previous current screen-file.
See SWAP-FILE CLOSE CLOSE-ALL
3. Tools
--------
Note: Most of these words are available only after the file TOOLS.SCR
has been loaded.
(* I S
Begin a block comment. Parse and discard text delimited by the
token *) . If the parse area is exhausted before the delimiter
is found refill the input buffer and resume the process.
An ambiguous condition exists if the delimiter is not found and
the parse area cannot be refilled.
Note: (* is primarily intended for text-files. May be relocated
to the kernel if/when it gains greater popularity.
-TOOLS ( -- a-addr ) S
A MARKER word used for deleting the tools utilities with FORGET.
See MARKER CHECKING
.FREE ( -- ) S
Display the current dictionary segments and statistics.
.S ( -- ) S
Display the values on the data and floating-point stacks.
? ( a-addr -- ) A
Display the single-cell value stored at a-addr. Display as signed
number if BASE is decimal or unsigned otherwise.
B ( -- ) S
Decrement variable SCR and list the screen.
See L N
DELETE ( "filename" -- ) S
Erase the specified file from disk. DELETE must not be performed
on an open file.
DIR ( "filename" -- ) S
List the current disk directory. Filename is required and may
include path and wildcards.
DUMP ( addr u -- ) S
Dump u bytes of memory starting at the address addr.
EDIT S
A synonym for the resident editor SED or TED. By default the
resident editor for DX.EXE is SED. See TED.TXT for details
on how to make TED the default editor.
See SED TED
FYI ( -- ) S
"For Your Information". Display information about the current
forth environment including dictionary segments, vocabularies,
logged drive and open screen-files. Formerly named MAP .
See .FREE VOCS ORDER
ICLOSE ( -- ) S
Close the current text-file.
INCLUDEd text-files are automatically closed after loading. If
an error occurs or loading is interrupted (e.g. QUIT was executed),
nested text-files may remain open preventing external editing or
cause difficulty loading ("too many files" error message). Should
this occur use ICLOSE or CLOSE-ALL to restore proper operation.
See INCLUDE INCLUDED CLOSE-ALL
INCLUDE ( "filename[.F]" -- ) S
Compile the text-file specified by the filename. If a filename
extension is not included then .F is assumed. Text-files may be
nested.
Note: Uses the default DTA buffer at address $80.
See INCLUDED ICLOSE
INCLUDED ( c-addr u -- ) S
Compile the text-file specified by the filename given by c-addr u.
If a filename extension is not included then .F is assumed.
Text-files may be nested.
Note: Uses the default DTA buffer at address $80.
See INCLUDE ICLOSE
INDEX ( +n1 +n2 -- ) S FIG
List line 0 of screens +n1 thru +n2 from the screen-file. Line 0
typically contains a comment indicating the contents of the screen.
See QX
L ( -- ) S
List the screen specified by variable SCR.
See N B
LASTFILE ( -- c-addr u ) S
Return a string containing the last filename processed by >FNAME.
Note: the string returned by LASTFILE remains valid for two
invocations of >FNAME e.g.
S" myfile" >FNAME DROP LASTFILE ( c-addr1 u1 )
S" yourfile" >FNAME DROP LASTFILE ( c-addr2 u2 )
CR TYPE SPACE TYPE
yourfile myfile ok
See >FNAME LOADFILE LOADLINE
LDUMP ( seg offs u -- ) S
Intersegment DUMP. Dump u bytes of memory starting at the address
specified by the 8086 segment/offset values.
LISTING ( -- ) S
List all screens from the screen-file to the printer, formatted 3
screens to the page. A form-feed character (0C hex) is output at
the end of each page.
LOADLINE ( -- a-addr ) S
A VARIABLE containing the current line number of the text-file
being INCLUDEd. Starting line number is 1.
See LASTFILE
LS ( -- ) S
Swap screen-files and list the screen specified by variable SCR.
See SWAP-FILE L
N ( -- ) S
Increment variable SCR and list the screen.
See L B
ORDER ( -- ) S
Display the context and current vocabularies.
QX ( +n -- ) S
Quick index. Starting with screen +n, list line 0 of 60 sequential
screens from the screen-file. Line 0 typically contains a comment
indicating the contents of the screen.
See INDEX
RENAME ( "oldfile" "newfile" -- ) S
Rename the specified disk file with a new name. RENAME must not
be performed on an open file.
SED ( | scr -- ) S
Invoke the screen-file editor. If SED is not resident then it is
first loaded. If scr is not specified then editing begins at the
position where the last error occured.
See EDIT TED
SHOW ( +n1 +n2 -- ) S
List screens +n1 through +n2 from the screen-file to the printer,
formatted 3 screens to the page. A form-feed character (0C hex) is
output at the end of each page.
TED ( | "filename[.F]" -- ) S
Invoke the text-file editor. If TED is not resident then it is
first loaded. If a filename is not specified then editing begins
at the line and file where the last error occured.
See EDIT SED
VOCS ( -- ) S
List all vocabularies beginning with the most recent.
WORDS ( -- ) S
Lists the names of forth words in the first search wordlist
beginning with the most recent. The color attribute is the same as
for .ID . fig-Forth equivalent is VLIST.
WORDS: ( "ccc" -- ) S
As for WORDS but takes a blank delimited string from the input
stream. Only word names containing the specified string are
listed. If the string is empty the result is the same as WORDS .
Formerly named WORDS-LIKE .
4. DOS Interface
----------------
BDOS ( DX x -- AL ) A
Perform MS-DOS INT 21H function call. Register DX holds the input
parameter. Low-order byte of x is the function number and is
passed to AH. The high-order byte of x is passed to AL. BX and CX
are set to zero. After the call the contents of AL is returned.
Note: This function has been superseded by DOSCALL.
CMDTAIL ( -- c-addr u ) A
Return the string representing the command tail entered at the DOS
prompt when the program was first initiated. Leading and trailing
blanks are stripped.
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
CSEG ( -- cseg ) A
Return the 8086 segment containing the DX-Forth code, data and
stacks.
See HSEG
DOSCALL ( u -- ) A
Call MS-DOS Interrupt 21H function u. DOSCALL is used similarly
to INTCALL with the exception that CPU registers AH and DS are
preloaded with function number u and DX-Forth segment CSEG
respectively. Refer to INTCALL for further details.
Example: retrieve the MS-DOS version
$30 DOSCALL 'AH C@ 'AX C@ ( minor major )
See DOSERR? INTCALL
DOSERR? ( -- ior ) A
Typically used following a DOSCALL or INTCALL to interrupt 21H.
MS-DOS generally uses the carry flag to report an error. DOSERR?
interrogates the carry flag and, if set, returns an ior value
corresponding to the MS-DOS error code contained in register AX.
If the carry flag was not set, ior is zero. In DX-Forth DOS
errors are returned as ior values in the range -511 to -257. To
convert these back to the MS-DOS error code use: ( ior) 255 AND
Note: Not all MS-DOS functions use the carry flag to indicate an
error. Refer to MS-DOS documentation to determine which functions
may use DOSERR? .
See INTCALL DOSCALL
DOSVER ( -- minor major ) A
Return DOS version number.
INTCALL ( u -- ) A
Call 8086 interrupt u. CPU register values are loaded into
variables before INTCALL and retrieved afterwards. The variables
used to hold the CPU register values are:
'AH 'BH 'CH 'DH 'AX 'BX 'CX 'DX 'BP 'SI 'DI 'DS 'ES 'FLAGS
Example: display the MS-DOS version
$30 'AH C! ( load AH = 30h )
$21 INTCALL ( perform INT 21h )
'AX C@ ( get AL )
. ( display major version )
See DOSERR? DOSCALL
P@ ( p-addr -- x ) A
Perform the 8086 IN instruction on 16-bit port p-addr returning x.
P! ( x p-addr -- ) A
Perform the 8086 OUT instruction sending x to the 16-bit port
p-addr.
PC@ ( p-addr -- x ) A
Perform the 8086 IN instruction on the 8-bit port p-addr returning
x. The upper 8 bits of x are set to zero. fig-Forth equivalent
is P@.
PC! ( x p-addr -- ) A
Perform the 8086 OUT instruction sending x to the 8-bit port
p-addr. fig-Forth equivalent is P!
5. Input/Output
---------------
(.) ( n -- c-addr u ) A
Convert the signed number n to a string c-addr u.
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
(D.) ( d -- c-addr u ) A
Convert the signed double number d to a string c-addr u.
Primitive for D.
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
(U.) ( u -- c-addr u ) A
Convert the unsigned number u to a string c-addr u.
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
. ( x -- ) A
Display single number x in free-field format with a trailing space
as a signed number if BASE is decimal or unsigned otherwise.
Note: This function adopts eForth behaviour in respect of BASE and
is useful for debugging. Applications requiring Forth-94 behaviour
may redefine:
: . ( n -- ) S>D D. ;
CONSOLE ( -- ) A
Redirect EMIT to the console screen.
D. ( d -- ) A
Display signed double number d in free-field format with a trailing
space.
EOL ( -- c-addr u ) A
Return the address/length of the string representing the system-
dependent end-of-line terminator. For CP/M and MS-DOS end-of-line
is CRLF ($0D $0A).
EOL DROP 1- ( -- c-addr ) returns a counted string
EOL DROP ( -- c-addr ) returns a null-terminated string
SYS-VEC ( -- addr ) A
Return the address of the system vector & parameter table.
offset type function parameter default
0 vKEY? xt KEY? -- flag ?terminal
2 vKEY xt KEY -- char conin
4 vEMIT xt EMIT char -- conout *
6 vCON xt CONSOLE out char -- conout
8 vLST xt PRINTER out char -- lstout
10 aINIT addr INIT patch -- NOOP *
12 aIDENT addr IDENTIFY patch -- NOOP *
14 aFNUMB addr FNUMBER patch c-addr u -- ?|0 FALSE *
16 nFPS u fp-stack size
18 aNUMB addr NUMBER? patch c-addr u -- ?|0 NUMBER?
20 nFPM u fp-stack min
22 nRTS u r-stack size
24 nUS u USER area size
26 nPNO u HOLD buffer size
28 nMSCON u MS timing constant
30 nTMODE u Timer 0 mode
* set according to mode or installed option
Sizes are expressed in bytes unless otherwise noted.
KEY ( -- char ) A 94
Receive the next character from the console.
Note: IBM-PC two-byte extended keystrokes are translated to a code
having a value of 128 or greater. Refer to DXFORTH.TXT for a
table of key codes.
KEY? ( -- flag ) A 94
Return true if a console key has been pressed. KEY is subsequently
used to retrieve the character. fig-Forth equivalent is ?TERMINAL.
PRINTER ( -- ) A
Redirect EMIT to the printer.
OUT ( -- a-addr ) A FIG
A USER variable that contains the number of characters output by
EMIT or TYPE since the last CR.
6. Arithmetic and Stack
-----------------------
-ROLL ( xu ... x1 x0 u -- x0 xu ... x1 ) A
Remove u. Rotate xu ... x1 to the top of the stack pushing x0 to
the position vacated by xu. The reverse of ROLL.
-ROT ( x1 x2 x3 -- x3 x1 x2 ) A
Rotate the top stack item to the third position. The reverse of
ROT.
2+ ( x1 -- x2 ) A 83 FIG
Add two (2) to n1|u1 giving the sum n2|u2.
2- ( x1 -- x2 ) A 83
Subtract two (2) to n1|u1 giving the sum n2|u2.
2NIP ( x1 x2 x3 x4 -- x3 x4 ) A
Drop cell pair x1 x2 from the stack leaving x3 x4.
>< ( x1 -- x2 ) A
Swap the high order byte (bits 8-15) with the low order byte
(bits 0-7) of x1.
FM/MOD ( d n1 -- n2 n3 ) A 94
Divide double number d by single n1, giving the floored quotient
n3 and the remainder n2.
LSHIFT ( x1 u -- x2 ) A 94
Perform a logical left shift of u bit-places on x1 giving x2.
Put zero into the least significant bits vacated by the shift.
M* ( n1 n2 -- d ) A 94
Multiply n1 by n2 giving the double result d.
M*/ ( d1 n1 +n2 -- d2 ) A 94
Multiply double number d1 by single n1 producing the triple
length intermediate result t. Divide t by +n2 giving the
double quotient d2.
M+ ( d1 n -- d2 ) A 94
Add single length number n to double d1, giving the sum d2.
NIP ( x1 x2 -- x2 ) A 94
Drop the first item below the top of stack.
NOT ( x -- flag ) A 79
Reverse the boolean value of x. Equivalent to: 0= .
Note: Do not confuse this function with FORTH-83 NOT which behaved
as INVERT.
RSHIFT ( x1 u -- x2 ) A 94
Perform a logical right shift of u bit-places on x1 giving x2.
Put zero into the most significant bits vacated by the shift.
SM/REM ( d n1 -- n2 n3 ) A 94
Divide d by n1, giving the single-cell remainder n2 and the single-
cell symmetric quotient n3. An ambiguous condition exists if n1 is
zero.
TUCK ( x1 x2 -- x2 x1 x2 ) A 94
Copy the first (top) stack item below the second stack item.
U2/ ( x1 -- x2 ) A
x2 is the result of shifting x1 one bit toward the least-significant
bit, leaving the most-significant bit zero. Functionally equivalent
to: 1 RSHIFT.
UMAX ( u1 u2 -- u1 | u2 ) A
Return the greater of two unsigned numbers.
UMIN ( u1 u2 -- u1 | u2 ) A
Return the lesser of two unsigned numbers.
7. Conversion
-------------
DPL ( -- a-addr ) A 83
A USER variable containing the number of places to the right of
the decimal point following number input conversion.
In DX-Forth DPL is incremented for each character successfully
converted by >NUMBER. Applications may use this feature to create
custom number conversion routines.
See NUMBER?
NUMBER? ( c-addr u -- d true | false ) A
Convert the case-insensitive string c-addr u to a double number
according to the current base. If successful, return double
number d and a true flag. A leading '-' character signifies a
negative number. If a punctuation character '.' occurs at the
end of the string then DPL is 0 otherwise it is -1. If conversion
is unsuccessful or the string was empty or contained blanks then a
false flag is returned and DPL is meaningless.
See DPL SYS-VEC
UPCASE ( c1 -- c2 ) A
Convert the character c1 to its uppercase equivalent c2.
Note: The name of this function is subject to change.
UPPER ( c-addr u -- ) A
Convert the character string c-addr u to uppercase.
Note: The name of this function is subject to change.
8. Strings and Memory
---------------------
!L ( x seg offs -- ) A
Store cell x at the 8086 segment/offset.
+STRING ( c-addr1 u1 c-addr2 u2 -- c-addr2 u3 ) A
Append the string c-addr1 u1 to the end of string c-addr2 u2
returning the resulting string c-addr2 u3. It is the programmer's
responsibility to ensure sufficient room is available at c-addr2
to hold both strings.
," ( "ccc<">" -- ) S
Parse the character string delimited by '"' and compile as a
counted string at HERE. The delimiter character may be included
in the string by entering it twice.
Note: In DX-Forth the memory occupied by ," strings is exactly
count+1 characters with no terminating null or alignment.
See /PARSE S,
-BLANKS ( c-addr1 u1 -- c-addr2 u2 ) A
Remove leading and trailing blanks from string c-addr1 u1 in the
SSEG segment leaving c-addr2 u2. Equivalent to: BL SKIP -TRAILING
See SSEG
-TRAILING ( c-addr u1 -- c-addr u2 ) A
Remove trailing blanks from string c-addr u1 in the SSEG segment
leaving c-addr u2. Equivalent to: BL TRIM
See TRIM SSEG
/PARSE ( char "ccc<char>" -- c-addr u ) S
Parse ccc delimited by char and store the string (255 characters
maximum) in a temporary buffer. The delimiter character may be
included in the string by entering it twice.
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
/PARSE is used by S" .( and ," . /PARSE and WORD share the same
buffer. Simultaneous use is allowed provided the combined length
of the strings does not exceed 255+31 chars. Formerly named
PARSE$ .
/STRING ( c-addr1 u1 n -- c-addr2 u2 ) A 94
Truncate the string c-addr1 u1 by n characters. The resulting
string c-addr2 u2 begins at c-addr1+n and has a length u1-n.
n may be negative.
2!L ( x1 x2 seg offs -- ) A
Store the cell pair x1 x2 at the 8086 segment/offset.
2@L ( seg offs -- x1 x2 ) A
Fetch the cell pair stored at the 8086 segment/offset.
@L ( seg offs -- x ) A
Fetch the cell stored at the 8086 segment/offset.
C!L ( char seg offs -- ) A
Store the lower-order 8 bits of char at the 8086 segment/offset.
C@L ( seg offs -- char ) A
Fetch the lower-order 8 bits of the character at the 8086 segment/
offset.
CAPS ( -- ) A
Causes the next occurrence of COMPARE or SEARCH to be performed as
if all characters in the source and destination strings were
uppercase. Used in the form:
( c-addr1 u1 c-addr2 u2 ) CAPS COMPARE
( c-addr1 u1 c-addr2 u2 ) CAPS SEARCH
Note: The effect of CAPS is temporary. It is automatically reset
by COMPARE SEARCH COLD, or when an error occurs and QUIT is
executed.
CELL- ( a-addr1 -- a-addr2 ) A
Subtract the size in address units of a cell to a-addr1, giving
a-addr2.
CMOVEL ( seg1 offs1 seg2 offs2 u -- ) A
Copy u consecutive characters starting at the 8086 segment/offset
seg1 offs1 to seg2 offs2, proceeding character-by-character from
lower addresses to higher addresses.
COMPARE ( c-addr1 u1 c-addr2 u2 -- -1 | 0 | 1 ) A 94
Compare string c-addr1 u1 in the SSEG segment with string c-addr2
u2. Return 0 if match, -1 if c-addr1 u1 is less than c-addr2 u2
or 1 if greater.
See CAPS SSEG
LFILL ( seg offs u char -- ) A
Store char in each of u consecutive characters of memory beginning
at the 8086 segment/offset.
MOVE ( a-addr1 a-addr2 u -- ) A 94
Move u bytes from a-addr1 to a-addr2. Overlap allowed.
OFF ( a-addr -- ) A
Clear all bits of the cell at a-addr. Functionally equivalent to:
0 a-addr !
ON ( a-addr -- ) A
Set all bits of the cell at a-addr. Functionally equivalent to:
TRUE a-addr !
PACK ( c-addr1 u c-addr2 -- c-addr2 ) A
Store the string c-addr1 u as a counted string at c-addr2 leaving
the destination address on the stack. The source and destination
strings are permitted to overlap. An ambiguous condition exists
if u is greater than 255 or the buffer at c-addr2 is less than
u+1 characters. Formerly named PACKED . Functionally equivalent
to: 2DUP 2>R CHAR+ SWAP CHARS MOVE 2R> TUCK C!
See PLACE
PAD ( -- c-addr ) A
Return the address of a transient region that can be used to hold
data for intermediate processing. PAD is at least 84 characters.
Note: In DX-FORTH PAD is located in the APPLICATION data-space
immediately above the pictured numeric output buffer. The maximum
size of PAD is: APPLICATION UNUSED PAD HERE - - U.
PLACE ( c-addr1 u c-addr2 -- ) A
Store the string c-addr1 u as a counted string at c-addr2. The
source and destination strings are permitted to overlap. An
ambiguous condition exists if u is greater than 255 or the buffer
at c-addr2 is less than u+1 characters. Equivalent to: PACK DROP
See PACK
S" ( "ccc<">" -- ) I S 94
( -- c-addr u ) run-time A
Parse a string (255 characters maximum) from the input stream
delimited by '"' and compile into the current definition. The
delimiter character may be included in the string by entering it
twice. At run-time, leave the string address and count on the
stack.
S" is state-smart. When interpreting, the string is placed in a
transient region which may be overwritten by subsequent operations.
See /PARSE
S, ( c-addr u -- ) S
Compile string c-addr u (255 characters maximum) as a counted
string at HERE.
Named STRING, $, in some Forth implementations.
Note: In DX-Forth the memory occupied by S, strings is exactly
count+1 characters with no terminating null or alignment.
See ,"
S.R ( c-addr n1 n2 -- ) A
Display string c-addr n1 right-aligned in a field n2 characters
wide. If the number of characters required to display the string
is greater than n2, all characters are displayed with no leading
spaces in a field as wide as necessary.
Equivalent to: OVER - SPACES TYPE
SCAN ( c-addr1 u1 char -- c-addr2 u2 ) A
Scan the string c-addr1 u1 in the SSEG segment for the character
char. Leave match address c-addr2 and length remaining u2. If
no match occurred then u2 is zero and c-addr2 is c-addr1 + u1.
See SSEG
SEARCH ( c-addr1 u1 c-addr2 u2 -- A 94
c-addr3 u3 -1 | c-addr1 u1 0 )
Search string c-addr1 u1 in the SSEG segment for the occurrence of
string c-addr2 u2. If found, return -1 and the match address
c-addr3 with u3 characters remaining.
See CAPS SSEG
SKIP ( c-addr1 u1 char -- c-addr2 u2 ) A
Skip leading occurrences of the character char in the string
c-addr1 u1 in the SSEG segment. Leave the address of the first
non-matching character c-addr2 and length remaining u2. If no
characters were skipped leave c-addr1 u1.
See SSEG
SLITERAL ( c-addr1 u -- ) compilation I S 94
( -- c-addr2 u ) run-time
Compile the string c-addr u (255 characters maximum) into the
dictionary. When later executed c-addr2 u is left on the stack.
SSEG ( -- a-addr ) A
A VARIABLE containing the segment of the first string used by
COMPARE SEARCH SCAN SKIP TRIM -TRAILING and ZCOUNT. By default
SSEG is set to the DX-Forth segment CSEG.
Note: The above words (and all that use them) will be affected
when SSEG is altered. Programs may temporarily change SSEG
provided it is restored to CSEG immediately afterwards. SSEG
is automatically reset by COLD or when an error occurs.
See CSEG
TRIM ( c-addr u1 char -- c-addr u2 -- ) A
Exclude trailing occurences of the character char in the string
c-addr u1 in the SSEG segment. Leave address c-addr and the
new length u2. If no characters were removed leave c-addr u1.
See SSEG
ZCOUNT ( c-addr -- c-addr u ) A
Return the address and length of the null-terminated string at
c-addr in the SSEG segment.
See SSEG
ZPLACE ( c-addr1 u c-addr2 -- ) A
Store the string c-addr1 u as a null-terminated string placed at
c-addr2. The move proceeds character by character starting with
the lower addresses.
9. Dictionary
-------------
(NAME) ( nfa -- c-addr u ) S
Return the string c-addr u representing the name of the forth word
whose name field address is nfa.
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
-? ( -- ) S
Suppress redefinition and system compilation warnings for the next
definition only.
See WARNING
.ID ( nfa | 0 -- ) S
Display the name of the forth word whose name field address is
nfa. If the word is nameless (nfa is zero) then "[noname]" is
displayed. Application words are shown with the NORMAL color
attribute while System words are in BOLD. Immediate words have
the brightness bit toggled. fig-FORTH equivalent is ID.
.NAME ( xt -- ) S
Display the name of the forth word whose execution token address
is xt. If the word is nameless or xt invalid then "[noname]" is
displayed. If the word is an alias then the primary name is
displayed. The color attribute is the same as for .ID
.VOC ( wid -- ) S
Display the name associated with wordlist wid. Wordlists may be
nameless in which case "[noname]" will be displayed.
See VOCABULARY W>NAME
APPLICATION ( -- ) A
Place subsequent definitions into the Application dictionary. The
application dictionary holds words that may be executed by TURNKEY
programs. Equivalent to: FALSE SYS !
Note: APPLICATION is the default mode on boot-up or COLD.
See SYS SYSTEM
BEHEAD ( "name1" "name2" -- ) S
Search the first wordlist in the search order and make invisible
the words between name1 and name2 inclusively. Beheaded words
will not be found in a wordlist search or displayed by WORDS. The
behaviour of beheaded words is not affected. An error message is
issued if the names reside in protected dictionary. Formerly named
EXCISE .
See CHECKING
CHAIN ( "name" -- ) S
Append vocabulary "name" to the base of the CURRENT wordlist. An
error message is issued if "name" is not a vocabulary, is the same
as, already chained, or created later than, the CURRENT vocabulary.
CONTEXT ( -- a-addr ) S
Returns the address of a 3-cell array which determines the
dictionary search order. The default search order in DX-Forth is
CONTEXT CURRENT FORTH. If wid is zero FIND moves to the next cell
in the array.
a-addr 1 cell wid CONTEXT
1 cell wid CURRENT
1 cell wid FORTH
See VOCABULARY CHAIN
DP ( -- a-addr ) A
A double USER variable containing pointers to the next free
address in the Application and System dictionaries respectively.
e.g.
DP @ ( -- appDP )
DP 2@ ( -- sysDP appDP )
DPH ( -- a-addr ) S
A USER variable containing a pointer representing the next free
address in the heads dictionary segment.
EMPTY ( -- ) S
Delete all definitions created since the last execution of COLD
or PROTECT. Compilation wordlist is set to FORTH.
See REMEMBER
FORGET ( "name" -- ) S 83 FIG
If word "name" is found in the compilation wordlist, delete it
and all words added to the dictionary after "name" was defined,
regardless of their wordlist. An error message is issued if
"name" is an alias or the word is located in the protected
dictionary.
See REMEMBER CHECKING PROTECT
HSEG ( -- hseg ) A
Return the 8086 segment containing the DX-Forth word headers.
See CSEG
HLIMIT ( -- addr ) S
A CONSTANT that returns the upper limit address of the heads
dictionary segment.
LAST ( -- a-addr ) S
A 2VARIABLE containing the name field and execution token address
of the latest definition.
LAST @ ( nfa )
LAST 2@ ( xt nfa )
LIMIT ( -- addr ) A FIG
A CONSTANT that returns the upper limit address of the application
dictionary and the start of the System dictionary.
LIMIT for TURNKEY applications will be the upper memory limit
currently used by the forth compiler (usually $FFF0) unless set
to a user-specified value with SET-LIMIT.
See SET-LIMIT
LINK, ( a-addr -- ) S
Add a node to linked list a-addr. The node is created at HERE
and consists initially of one cell containing the address of the
previous node. Equivalent to: HERE OVER @ , SWAP !
MARKER ( "name" -- ) S
A defining word used in the form:
MARKER name
Typically used to mark the beginning of an application which may
later be removed by executing FORGET name. "name" is placed in
the System dictionary. Executing "name" is a no-operation.
Note: MARKER differs from the Forth-94 specification.
N>NAME ( nfa1 -- nfa2 | 0 ) S
Given the name field address of a word, return the nfa of the
previous word in the wordlist. If the end of the wordlist is
reached then 0 is returned.
PROTECT ( -- ) S
Protect the current state of the dictionary. Existing definitions
can no longer be forgotten. Formerly named FREEZE .
See CHECKING
REMEMBER ( xt -- ) S
Append execution token xt to the REMEMBER list.
When words are discarded or the dictionary is otherwise reduced,
xt's in the REMEMBER list that lie outside the new dictionary
boundary will be executed beginning with the most recent.
Typically xt represents a function whose purpose is to restore
critical system values to their previous state. Executed xt's
are automatically removed from the REMEMBER list.
Note: Functions executed from the REMEMBER list are run only after
the new dictionary boundary has been established. Consequently
these functions may be residing in free memory when executed.
See FORGET EMPTY
SET-LIMIT ( addr -- ) S
Set the value of LIMIT for TURNKEY applications to addr. If addr
does not lie on a 16-byte boundary, it is first rounded down.
Typically used prior to executing TURNKEY.
SET-LIMIT only affects applications saved with TURNKEY. It is
the programmer's responsibility to ensure sufficient memory is
available for the demands of the application. The address passed
to SET-LIMIT remains in effect until a new value is set, or is
cancelled by executing COLD in the forth environment e.g. rebooting
the system.
See LIMIT UNUSED
SYS ( -- a-addr ) A
A VARIABLE that determines the compilation dictionary. Definitions
will be compiled to the system dictionary if SYS is non-zero and to
the application dictionary if zero.
See APPLICATION SYSTEM
SYSTEM ( -- ) S
Place subsequent definitions into the System dictionary. The
System dictionary holds the compiler and other support functions
not generally required for TURNKEY applications.
Equivalent to: TRUE SYS !
See SYS APPLICATION
VOC-LINK ( -- a-addr ) S FIG
A USER variable containing a pointer to the most recently defined
wordlist.
VOCABULARY ( "name" -- ) S 83
Create a new empty wordlist. When "name" is later executed replace
the first wordlist in the search order with the wordlist associated
with "name". ADDR "name" @ returns the wordlist identifier wid.
W>NAME ( wid -- nfa | 0 ) S
Return the name field address of the most recently defined word in
wordlist wid. If the wordlist is empty then zero is returned.
WARNING ( -- a-addr ) S
A VARIABLE that controls warning messages. When set to zero, word
redefinition and System compilation warnings are disabled. Users
may set WARNING to TRUE or FALSE (e.g. using ON or OFF ) - other
values must not be used.
See -?
10. Facility
------------
/MS ( -- ) A
Adjust MS for correct operation.
Note: This function is executed at start-up by COLD and is not
normally required thereafter. It is provided for applications
which switch Timer 0 between modes 2 and 3 thereby affecting
MS SOUND BEEP. SYS-VEC holds the timer mode in use when /MS was
last executed.
Note: /MS is a DEFERed word.
See SYS-VEC
AT-XY ( x y -- ) A 94
Move the cursor to the specified coordinates relative to the
current text window.
Note: No bounds checking of x,y is performed.
See GET-XY
ATTRIB ( -- addr ) A
A byte variable containing the current text mode video attribute.
May be used to determine or modify the current screen colors and
blink mode. Bitfields for the attribute byte are:
7 blink/intensity
6-4 background color 0-7
3-0 foreground color 0-15
Colors:
0 black 8 dark gray
1 blue 9 light blue
2 green 10 light green
3 cyan 11 light cyan
4 red 12 light red
5 magenta 13 light magenta
6 brown 14 yellow
7 light gray 15 white
Note: COLD resets ATTRIB to the video attribute in force when
the application was booted. Executing QUIT or entering the forth
development environment causes ATTRIB to be set to the NORMAL
attribute as defined in COLOR-TABLE.
See RETURN
BEEP ( -- ) A
Generate a bell sound. Uses SOUND and MS.
Note: BEEP is a DEFERed word.
BACKGROUND ( x -- ) A
Change the text window background to color x. x = 0-7
See ATTRIB
BOLD ( -- ) A
Begin 'bold' video mode.
See NORMAL COLOR-TABLE
BRIGHT ( -- ) A
Begin 'bright' video mode.
See NORMAL COLOR-TABLE
CLEAR-LINE ( -- ) A
Delete all characters from the current cursor position to the end
of the line. The cursor position remains unchanged.
COLOR-TABLE ( -- addr ) A
Return the address of a 4-byte table containing text mode video
attributes NORMAL INVERSE BOLD BRIGHT. The default values are
$07 $70 $03 $0B respectively.
Note: Used by the forth system. Modification by applications is
discouraged - use ATTRIB instead.
See ATTRIB
DELETE-LINE ( -- ) A
Delete the line at the current cursor position. All subsequent
lines are moved up one position. An empty line appears at the
bottom of the screen.
FOREGROUND ( x -- ) A
Change the text window foreground to color x. x = 0-15
See ATTRIB
GET-WINDOW ( -- x1 y1 x2 y2 ) A
Return the current text window boundary expressed as co-ordinates
of the default window. Formerly named WINDOW? .
See SET-WINDOW
GET-XY ( -- x y ) A
Return the current cursor position relative to the current text
window. Formerly named AT-XY? .
See AT-XY
INSERT-LINE ( -- ) A
Insert an empty line at the current cursor position. All
subsequent lines in the text window are moved down one position.
The bottom line is lost.
INVERSE ( -- ) A
Begin 'inverse' video mode.
See NORMAL COLOR-TABLE
MS ( u -- ) A 94
Delay u milliseconds. Uses Timer 0 and performs a PAUSE each 4mS.
Note: MS is a DEFERed word.
See /MS
NORMAL ( -- ) A
Begin 'normal' video mode. Used by QUIT and BYE .
See BOLD COLOR-TABLE
PAGE ( -- ) A 94
For the console, clear the text screen window and place the cursor
at the upper left; otherwise output a formfeed character (0C hex).
In DX-Forth, PAGE is equivalent to: 12 EMIT
See CONSOLE PRINTER
SET-WINDOW ( x1 y1 x2 y2 -- ) A
Define a text window with an upper-left corner x1 y1 and lower-
right corner x2 y2. Formerly named WINDOW .
See GET-WINDOW
SOUND ( u1 u2 -- ) A
Generate a tone with a frequency of u1 hertz for a duration of
u2 milliseconds. If u1 is less than 19 then only a delay of the
specified duration results. Performs a PAUSE each 4mS. Uses
Timer 2.
Note: SOUND is a DEFERed word.
TICKS ( -- d ) A
Return time-of-day (TOD) i.e. the number of BIOS timer ticks
since midnight (0..1573039). Each tick represents 54.9254 mS.
WAIT-TICK ( -- ) A
Wait until the next BIOS timer tick. Typically used to
synchronize program execution to the BIOS tick timer.
See TICKS
11. Miscellaneous
-----------------
#USER ( -- +n ) S
A VALUE returning the number of bytes in the USER area reserved by
the forth system. #USER marks the offset at which applications
may begin defining USER variables.
See USER
'NEXT ( -- addr ) A
Return the address of the centralized NEXT routine - the forth
"address interpreter".
Note: In DX-Forth for DOS, most code words use an in-line NEXT
for speed.
'SOURCE ( -- a-addr ) S
A double variable containing the current parameters for SOURCE.
'SOURCE 2@ is the equivalent of SOURCE.
(EXIT) ( -- ) A
Note: As of DX-Forth 4.30 this word has been renamed to EXIT.
--> ( -- ) I S 83 FIG
Continue interpretation on the next sequential block. May be
used within a colon definition that crosses a block boundary.
-ALLOT ( u -- ) A
If u is greater than zero, release u address units of data space.
If u is zero, leave the data-space pointer unchanged. No memory
checking is performed. -ALLOT may be used within turnkey
applications.
See ALLOT
@EXECUTE ( i*x a-addr -- i*y ) A
Execute xt located at address a-addr. If xt is zero then no
action is performed. Other stack effects are due to the word
executed.
Named PERFORM in some Forth implementations.
ABORT ( i*x -- ) ( R: j*x -- ) A 94
Empty the data stack and perform the function of QUIT which
includes emptying the return stack. No message is displayed.
For turnkey applications perform 1 RETURN .
In DX-Forth ABORT performs -1 THROW .
See QUIT
ABORT" ( "ccc<">" -- ) I S 94
( i*x flag -- ) ( R: j*x -- ) run-time A
If flag is non-zero display the character string delimited by '"'
and perform the function of ABORT.
In DX-Forth ABORT" performs -2 THROW and is state-smart.
ADDR ( "name" -- a-addr ) I S
"address of". Return the data field address of the word "name".
An ambiguous condition exists if "name" was not created by VALUE
DEFER CREATE VARIABLE 2VARIABLE CONSTANT 2CONSTANT USER VOCABULARY
and other functions as may be specified.
Named &OF or & in some Forth implementations.
ADDR is state-smart.
AKA ( "oldname" "newname" -- ) S
"Also Known As". Create an alias name "newname" for existing word
"oldname". If oldname was immediate then newname will be
immediate.
Note: In DX-Forth aliases consume only header space, and the xt of
an alias is the same as the xt of the original word. The function
appears in other Forth implementations albeit with different names
and usage e.g. SYNONYM ALIAS .
ALLOT ( u -- ) A
If u is greater than zero, reserve u address units of data space.
space. If u is zero, leave the data-space pointer unchanged. An
error occurs if insufficient data space is available. ALLOT may
be used within turnkey applications.
Note: Forth-94 permits ALLOT to use signed values. As of DX-Forth
for DOS v4.03 only unsigned values (0 to 65535) may be used with
ALLOT. Releasing data space is now done with -ALLOT. This change
was necessary to permit robust memory checking within ALLOT.
Applications requiring Forth-94 behaviour may redefine:
: ALLOT ( n -- ) NEGATE -ALLOT ;
however no memory checking will be performed.
See -ALLOT UNUSED
BETWEEN ( n1|u1 n2|u2 n3|u3 -- flag ) A
Perform a comparison of a test value n1|u1 with a lower limit
n2|u2 and an upper limit n3|u3, returning true if either (n2|u2
<= n3|u3 and (n2|u2 <= n1|u1 and n1|u1 <= n3|u3)) or (n2|u2 >
n3|u3 and (n2|u2 < n1|u1 or n1|u1 < n3|u3)) is true, returning
false otherwise. An ambiguous condition exists if n1|u1, n2|u2,
and n3|u3 are not all the same type.
This is similar to WITHIN with the exception that the limits are
inclusive.
See WITHIN
BIOS-IO ( -- ) A
Set console output and keyboard input to use BIOS calls. BIOS-IO
provides color and window support without the need for ANSI.SYS.
BIOS-IO is the default mode and is reset when an error occurs and
QUIT is executed.
See DOS-IO
BOUNDS ( addr1 u -- addr1+u addr1 ) A
Convert the memory specified by addr1 u to start/end addresses
suitable for DO LOOP.
BUILD ( xt "name" -- ) S
Skip leading space delimiters. Parse name delimited by a space.
Create a definition for name with the execution semantics specified
by xt. When name is executed name's data field address is placed
on the data stack and execution proceeds according to the semantics
given by xt.
BUILD provides an alternative to CREATE ... DOES> . Typical use:
SYSTEM
: CONSTANT ['] @ BUILD , ;
APPLICATION
BUILD may be used outside a definition e.g.
\ return string representing end-of-line sequence
' COUNT BUILD EOL ( -- c-addr u ) 2 C, $0D C, $0A C,
\ print a number in alternate radix
\ adapted from a posting by "Bee" on c.l.f.
:NONAME ( a-addr -- )
BASE @ >R C@ BASE ! U. R> BASE ! ; ( xt)
( xt) DUP BUILD B. ( u -- ) 2 C,
DUP BUILD O. ( u -- ) 8 C,
BUILD H. ( u -- ) 16 C,
\ interpret a number in an alternate radix
:NONAME ( "number" -- x )
BASE @ >R C@ BASE ! TOKEN NUMBER?
R> BASE ! 0= ABORT" bad radix" DROP
STATE @ IF POSTPONE LITERAL THEN ; ( xt)
( xt) DUP BUILD D# 10 C, IMMEDIATE
DUP BUILD B# 2 C, IMMEDIATE
BUILD H# 16 C, IMMEDIATE
BYE ( -- ) S 94
Perform CLOSE-ALL CONSOLE NORMAL then return to DOS with 0 RETURN.
CASE ( C: -- mark ) I S 94
Mark the start of a CASE construct. Used in the form:
CASE x1
x2 OF ... ENDOF
x3 OF ... ENDOF
( x1)
ENDCASE
In DX-Forth CASE is a synonym for COND .
CATCHER ( -- a-addr ) A
A USER variable containing the last exception handler. If the
contents is zero no more exception frames (installed by CATCH)
are present.
CHAR ( -- c ) S 94
Parse the next word in the input stream and return the ASCII
value of the first character.
COLD ( -- ) A FIG
Cold restart the forth environment or turnkey application.
COMPILE S 83
COMPILE is obsolete and should not be used directly in
applications. COMPILE is a factor of POSTPONE and is present in
the dictionary as a named word for error handling purposes.
COND ( C: -- mark ) I S
Mark the start of a COND construct. Used in the form:
COND x1
x2 OF ... ELSE
x3 OF ... ELSE
( x1)
THENS
COND x1
x2 EQUAL x3 x4 RANGE WHEN ... ELSE
( x1)
See THENS "Miser's CASE" CASE
CONSTANT ( x "name" -- ) S
Create a definition for name. When "name" is later executed
the numeric value x is placed on the stack.
Note: In DX-Forth the parameter field of a CONSTANT may be less
than 16 bits. Applications which read/write directly to the
parameter field of a CONSTANT should be modified to use VALUE
instead e.g. CONSTANT ... DOES> @ should be replaced with
VALUE ... DOES> @ .
DEFER ( "name" -- ) S
Creates a deferred word whose action word may be subsequently
altered using the sequence: ' ccc IS name
Deferred words are used to create forward references that will be
resolved later. A run-time error occurs if an attempt is made to
execute an uninitiated deferred word.
Note: The current action of a deferred word may be obtained
using
' >BODY @ ( "name" -- xt ) or
ADDR @ ( "name" -- xt )
See IS
DOS-IO ( -- ) A
Set console output and keyboard input to use DOS calls. May be
used to support redirection, screen pausing and control-C/Break in
applications.
Note: Color and windowing functions do not function in DOS-IO mode.
Control-C/Break keys are not trapped and will cause an immediate
exit to DOS.
See BIOS-IO
DXFORTH ( -- minor major ) A
Return the DX-Forth version number.
END ( -- ) ( C: orig -- ) I S
Mark the end of an IF or other conditional that leaves an orig
on the control stack. At run-time exit the current definition.
Equivalent to the sequence EXIT THEN .
Example:
IF ... EXIT THEN
becomes
IF ... END
ENDCASE ( x -- ) I S 94
Mark the end of a CASE construct. Discard x. In DX-FORTH ENDCASE
is equivalent to DROP THENS .
See CASE OF ENDOF THENS
ENDOF ( -- ) I S 94
Mark the end of an OF ENDOF pair. In DX-FORTH ENDOF is a synonym
for ELSE .
See CASE OF ENDCASE
EVALUATE ( c-addr u -- ) S 94
Save the current input source specification. Make the string
described by c-addr u both the input source and input buffer,
set >IN to zero, and interpret. When the parse area is empty,
restore the prior input source specification.
EXIT ( -- ) A 94
Exit the current colon definition and return control to the
calling definition.
FDB ( -- a-addr ) S
Get the address of the next free file descriptor block. If no more
free descriptors exist the function aborts with a "too many files"
error message.
Note: FDB is used by the system to load screen/text source-files
and is not normally an end-user function.
I' ( -- x ) ( R: loop-sys -- loop-sys ) A
Copy the current (innermost) loop limit to the data stack.
INTERPRET ( -- ) S FIG
Successively interpret forth text from the input stream until
exhausted, compiling or executing depending upon STATE. If an
error occurs the process aborts with a message.
The interpreter recognizes the numeric prefixes # $ % for decimal,
hexadecimal and binary respectively.
IS ( xt "name" -- ) I S
Used in the form:
' ccc IS name
where "name" is a deferred word and ccc defines the new behaviour.
See DEFER
NHOLD ( +n char -- ) A
Perform HOLD n times. An ambiguous condition exists if n < 0.
See SHOLD
NOOP ( -- ) A
No operation. Typically used to set a null action e.g.
' NOOP IS XXX
where XXX is a DEFERed word.
OF ( x1 x2 -- ) I S 94
If x1 = x2, discard both values and perform the sequence between OF
and ENDOF. Execution then continues after ENDCASE . If x1 <> x2,
discard x2 and continue after the corresponding ENDOF.
Note: In DX-FORTH OF is functionally equivalent to the sequence
OVER = IF DROP and thus may be used outside a CASE statement e.g.
: EOL? ( char -- 2|1|0 )
$0D OF 2 END
$0A OF 1 END
DROP 0 ;
See CASE ENDOF ENDCASE COND THENS
PAUSE ( -- ) A
Provides support for multitasking applications. When the
multitasker is loaded and enabled, PAUSE passes control to the next
task. Refer to the multitasking documentation for further details.
Note: PAUSE is automatically executed by KEY? KEY EMIT MS
QUIT ( -- ) ( R: i*x -- ) A 83
Empty the return stack, make the user input device the input
source and enter interpretation state. No message is displayed
and the data stacks are not emptied. For turnkey applications
perform the function 0 RETURN .
Like ABORT, QUIT may be used to terminate an application at any
nesting level. Unlike ABORT, QUIT in DX-Forth is not considered
an error condition and cannot be intercepted with CATCH.
Note: Prior to DX-Forth 4.2 QUIT was a System word and could not
be used to exit turnkey applications.
See ABORT
R0 ( -- a-addr ) A FIG
A USER variable that contains the address of the top of the return
stack.
RETURN ( x -- ) A
Restore initial drive/path then return to DOS with exit code x
where x is a value in the range 0 to 255. Open files are not
closed.
Note: The MS-DOS version automatically restores the initial DOS
text colors; however to be effective the cursor must be located on
the bottom screen line when RETURN is called. An alternative is
to simply type CLS from the DOS prompt when the application exits.
See ABORT QUIT BYE
RP! ( addr -- ) A
Set the return stack pointer to addr.
RP@ ( -- addr ) A FIG
Return the address of the current return stack pointer.
S0 ( -- a-addr ) A FIG
A USER variable that contains the address of the top of the
data stack.
SAVE ( "filename[.EXE]" -- ) S
Save the current forth system image to disk including any new
definitions created.
See TURNKEY TURNKEY-SYSTEM
SHOLD ( c-addr u -- ) A
Add string c-addr u to the beginning of the pictured numeric
output string.
See NHOLD
SP! ( addr -- ) A
Set the data stack pointer to addr.
SP@ ( -- addr ) A FIG
Return the address of the current data stack pointer.
THENS ( C: mark -- ) I S
Resolve a COND/CASE construct.
Similar to ENDCASE but does not expect the case selector to be on
the stack. Named END-CASE in some Forth implementations.
See COND "Miser's CASE"
TO ( x "name" -- ) S 94
Set the contents of VALUE name to x.
See VALUE
TOKEN ( "name" -- c-addr u ) S
Parse a blank-delimited name token from the input stream. A space,
not included in the length, follows the string.
Equivalent to: BL WORD COUNT
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
See WORD
TURNKEY ( "bootword" "filename[.EXE]" -- ) S
Save a standalone application to disk using the specified filename.
When the application is subsequently run, execution begins with
bootword and ends with 0 RETURN if successful, or 1 RETURN if
ABORT ABORT" or an uncaught error was encountered.
Note: System dictionary and word headers are not saved by TURNKEY
and therefore unavailable to the saved application.
See SAVE TURNKEY-SYSTEM
TURNKEY-SYSTEM ( "bootword" "filename[.EXE]" -- ) S
Save a standalone application including the System dictionary and
heads to disk using the specified filename. When the application
is subsequently run, execution begins with bootword and ends with
0 RETURN if successful, or 1 RETURN if ABORT ABORT" or an
uncaught error was encountered.
TURNKEY-SYSTEM is used for applications that require access to
words in the System dictionary.
See SAVE TURNKEY
UNNEST ( -- ) ( R: nest-sys -- ) A
Discard the calling definition specified by nest-sys. Before
exiting the current definition, a program shall remove any
parameters the calling definition had placed on the return stack.
An ambiguous condition exists if the current or calling definition
uses locals.
UNUSED ( -- u ) A 94
Return the amount of data space in bytes remaining in the region
addressed by HERE. The calculation includes a 255 byte safety
margin.
See APPLICATION SYSTEM
UP ( -- a-addr ) A
A VARIABLE that contains the base address of the current USER
area.
USER ( +n "name" -- ) S FIG
A defining word used in the form:
+n USER name
which creates a USER variable "name". +n is the offset within
the user area where the value for "name" is stored. Executing
"name" leaves the address of the variable in the user area.
USER variables with offsets #USER and higher are available for
use by applications.
Note: Offsets numbers are subject to change. When an offset
is required by an application, it should be determined at
compile-time e.g. [ BASE UP @ - ] LITERAL will return the
offset for BASE .
See #USER
VALUE ( x "name" -- ) S 94
As for CONSTANT but with the exception the data field of a VALUE
is always 1 cell and the contents may be changed using TO.
See CONSTANT
WITHIN ( x1 x2 x3 -- flag ) A 94
Return true if x3 lies within the range x1 to x2-1, otherwise
return false. x may be signed or unsigned.
See BETWEEN
WORD ( char "ccc" -- c-addr ) S 83
Parse a string from the input stream delimited by char leaving a
counted string at c-addr. Leading instances of char are skipped.
A space, not included in the length, follows the string.
Note: The returned string resides in a transient region which may
be overwritten by subsequent operations.
See TOKEN
Y/N ( -- flag ) A
Display '(y/n) N' and wait for a single console key. Return
true if the 'Y' or 'y' key was pressed or false otherwise.
[CHAR] ( -- c ) I S 94
Parse the next word in the input stream and compile the ASCII
value of the first character as a literal.
[DEFINED] ( "name" -- flag ) I S
Parse the next word in the input stream. Return a true flag if
word was defined in the dictionary.
[IF] [ELSE] [THEN] I S 94
These are the equivalents of IF ELSE THEN but may be used outside
a definition.
[UNDEFINED] ( "name" -- flag ) I S
Parse the next word in the input stream. Return a true flag if
word was not defined in the dictionary.
\ ( -- ) I S 94
Skip the rest of the line and resume interpretation at the
beginning of the next line.
\\ ( -- ) I S
Parse and discard the remainder of the parse area. If the source
is a text-file the remainder of the file is discarded.
12. Floating Point
------------------
By default DX-Forth uses single precision software floating point.
A real number occupies two cells (4 bytes) with a maximum precision
of 7 digits and a dynamic range of 5E-39 to 1E38.
The forth interpreter recognizes a number as floating point if it is
in decimal mode and contains an exponent identifier 'E' e.g. 1.0E
3.141952E 1e-12
DX-Forth for DOS v2 and higher use a separate stack for floating point
operations. If a common stack floating point model is desired (as used
in DX-Forth 1.0), it may be achieved by changing the 'fstack' equate
to 'no' in the DX-Forth source code and re-assembling. If you have
Borland TASM simply execute MAKEF.BAT and it will generate both models
without any need to alter the source.
Notes:
- In the common stack model, variables FS0 and FSP are dummies. Their
contents are initialized as for S0 but are otherwise unused.
- Available output modes
Compact Formatted String
------- --------- ------
F. F.R (F.) Floating
FS. FS.R (FS.) Scientific
FE. FE.R (FE.) Engineering
G. G.R (G.) General
In compact (floating-point) mode non-essential zeros and signs are
removed and the number of significant digits output is limited to a
maximum of PRECISION digits. In formatted (fixed-point) mode the
number of places output after the decimal point is specified by the
user and PRECISION has no effect. Output words that specify the
number of places after the decimal point may use the value -1 to
force compact mode. F. FS. FE. G. always use compact mode.
The character string returned by (F.) (FS.) (FE.) (G.) resides in the
pictured-numeric output area. An ambiguous condition exists if BASE
is not decimal or the character string exceeds the pictured-numeric
output area.
(F.) ( r n -- c-addr u ) A
Convert real number r to string c-addr u in fixed-point notation
with n places to the right of the decimal point. If n = -1, non-
essential zeros and signs are removed. Primitive used by F. F.R
(FE.) ( r n -- c-addr u ) A
Convert real number r to string c-addr u in engineering notation
with n places right of the decimal point. If n = -1, non-essential
zeros and signs are removed. Primitive used by FE.
FE.R
(FS.) ( r n -- c-addr u ) A
Convert real number r to string c-addr u in scientific notation
with n places right of the decimal point. If n = -1, non-
essential zeros and signs are removed. Primitive used by FS. FS.R
(G.) ( r n -- c-addr u ) A
Convert real number r to string c-addr u with n places right of
the decimal point. Fixed-point notation is used if the exponent is
in the range -4 to 5 otherwise use scientific notation. If n = -1,
non-essential zeros and signs are removed. Primitive used by G.R G.
-FP ( -- a-addr ) S
A MARKER word used to delete the floating-point with FORGET.
See MARKER CHECKING
>FLOAT ( c-addr u -- r true | false ) A 94
Convert the string c-addr u to a real number. If successful,
return the real number r and true or false otherwise.
Note: A zero length string or a string with leading blanks will
return the real number 0.0E and true.
D>F ( d -- r ) A 94
Convert the double number to its real number equivalent.
F! ( r f-addr -- ) A 94
Store r at f-addr.
F* ( r1 r2 -- r3 ) A 94
Multiply r1 by r2, giving the product r3.
F** ( r1 r2 -- r3 ) A 94
Raise r1 to the power r2.
F+ ( r1 r2 -- r3 ) A 94
Add r1 to r2, giving the sum r3.
F, ( r -- ) S
Reserve one floating-point cell of data space and store r in the
cell.
F- ( r1 r2 -- r3 ) A 94
Subtract r2 from r1, giving the difference r3.
F. ( r -- ) A
Display r in floating-point notation followed by a space.
Non-essential zeros and signs are removed.
F.R ( r n u -- ) A
Display r in fixed-point notation right-justified in a field
width u with n places right of the decimal point. If n = -1,
non-essential zeros and signs are removed.
F/ ( r1 r2 -- r3 ) A 94
Divide r1 by r2, giving the quotient r3.
F0< ( r -- flag ) A 94
Return true if r is less than zero, or false otherwise.
F0= ( r -- flag ) A 94
Return true if r is equal to zero, or false otherwise.
F0> ( r -- flag ) A
Flag is true if r is greater than zero.
F< ( r1 r2 -- flag ) A 94
Return true if r1 is less than r2, or false otherwise.
F> ( r1 r2 -- flag ) A
Flag is true if r1 is greater than r2.
F>D ( r -- d ) A 94
Convert the integer part of r to its double number equivalent.
F>S ( r -- n ) A
Convert the integer part of r to its single number equivalent.
F@ ( f-addr -- r ) A 94
Return the value of the real number stored at f-addr.
FABS ( r1 -- r2 ) A 94
Return the absolute value of r1.
FATAN ( r1 -- r2 ) A 94
r2 is the principal radian angle whose tangent is r1.
FCONSTANT ( r -- ) compilation A 94
( -- r ) run-time
Define a floating point constant having the value r.
FCOS ( r1 -- r2 ) A 94
r2 is the cosine of the radian angle r1.
FDP ( -- a-addr ) A
A VARIABLE that controls floating decimal point display. If zero
then trailing decimal points are not shown; if non-zero a decimal
point is always shown. Default is FDP ON.
FDROP ( r -- ) A 94
Remove r from the stack.
FDUP ( r -- r r ) A 94
Duplicate r.
FE. ( r -- ) A
Display r in engineering notation followed by a space. Non-
essential zeros and signs are removed.
FE.R ( r n u -- ) A
Display r in engineering notation right-justified in a field width
u with n places to the right of the decimal point. If n = -1,
non-essential zeros and signs are removed.
FEXP ( r1 -- r2 ) A 94
Raise e to the power r1, giving r2.
FLITERAL ( r -- ) compilation A 94
( -- r ) run-time
Compile r into the dictionary. When later executed r is left on
the stack.
FLN ( r1 -- r2 ) A 94
r2 is the natural logarithm of r1.
FLOOR ( r1 -- r2 ) A 94
Round r1 to an integral value using the "round toward negative
infinity" rule, giving r2.
FMAX ( r1 r2 -- r3 ) A 94
r3 is the maximum of r1 and r2.
FMIN ( r1 r2 -- r3 ) A 94
r3 is the minimum of r1 and r2.
FNEGATE ( r1 -- r2 ) A 94
Negate r1, giving r2.
FOVER ( r1 r2 -- r1 r2 r1 ) A 94
Place a copy of r1 on top of the stack.
FPICK ( ru ... r0 u -- ru ... r0 ru ) A
Remove u. Copy ru to the top of the stack.
FRANDOM ( r1 -- r2 ) A
If r1 is a positive non-zero number, return a pseudo-random number
r2 uniformly distributed in the range 0.0E to (but not including)
1.0E. If r1 is zero, return the last random number generated. If
r1 is negative, r1 is used to re-seed the random number generator.
FROT ( r1 r2 r3 -- r2 r3 r1 ) A 94
Rotate r1 to the top of the stack.
FROUND ( r1 -- r2 ) A 94
Round r1 to an integral value using the "round to nearest" rule,
giving r2.
FS. ( r -- ) A
Display r in scientific notation followed by a space. Non-
essential zeros and signs are removed.
FS.R ( r n u -- ) A
Display r in scientific notation right-justified in a field width
u with n places to the right of the decimal point. If n = -1,
non-essential zeros and signs are removed.
FS0 ( -- a-addr ) A
A USER variable that contains the address of the top of the
separate floating point stack.
Note: Has no function in the common stack floating point model
FSIN ( r1 -- r2 ) A 94
r2 is the sine of the radian angle r1.
FSP ( -- a-addr ) A
A VARIABLE that returns the address of the current separate
floating point stack pointer.
Note: Has no function in the common stack model
FSQRT ( r1 -- r2 ) A 94
r2 is the square root of r1.
FSWAP ( r1 r2 -- r2 r1 ) A 94
Exchange the top two floating point numbers.
FVARIABLE ( -- ) compilation A 94
( -- f-addr ) run-time
Define a floating point variable.
G. ( r -- ) A
Display real number r in floating-point notation followed by a
space. If the exponent is outside the range -4 to 5 then
scientific notation is used. Non-essential zeros and signs are
removed.
G.R ( r n u -- ) A
Display real number r right-justified in a field width u with n
places right of the decimal point. Fixed-point notation is used
if the exponent is in the range -4 to 5 otherwise use scientific
notation. If n = -1, non-essential zeros and signs are removed.
MAX-PRECISION ( -- u ) A
A CONSTANT returning the implementation-defined maximum PRECISION.
See SET-PRECISION
PI ( -- r ) A
An FCONSTANT that returns the value for "pi" (3.141593..)
PRECISION ( -- u ) A 94
Return the maximum number of significant digits currently used by
F. FS. FE. G. and in compact output mode F.R FS.R FE.R G.R (F.)
(FS.) (FE.) (G.) .
REPRESENT ( r c-addr n1 -- n2 flag1 flag2 ) A 94
DX-Forth uses an enhanced REPRESENT. It follows the Forth-94
definition with the following extensions:
- if n1 is zero the entire significand of r is rounded to one or
zero following the system's rounding rule; if n1 is negative
then r is rounded to zero.
- the buffer size allocated at c-addr shall be the greater of n1
or MAX-PRECISION.
See http://dxforth.netbay.com.au/Represent_33.txt
S>F ( n -- r ) A
Convert the single number to its real number equivalent.
SET-PRECISION ( u -- ) A 94
Set the maximum number of significant digits used by F. FS. FE.
G. and in compact output mode F.R FS.R FE.R G.R (F.) (FE.) (FS.)
(G.) . u is limited to MAX-PRECISION.
13. Compiler Security
---------------------
!CSP ( -- ) S FIG
Save the current data stack position. Equivalent to: SP@ CSP !
See ?CSP
?BAL ( flag -- ) S
Issue an error message 'definition unbalanced' and abort if flag
and CHECKING are not zero.
See CHECKING
?CSP ( -- ) S FIG
Issue an error message 'definition unbalanced' and abort if the
current data stack position does not match the value saved by !CSP
and CHECKING is not zero.
See CHECKING
?COMP ( -- ) S FIG
Issue an error message 'compilation only' and abort if not
compiling.
?EXEC ( -- ) S FIG
Issue an error message 'execution only' and abort if not
executing.
?STACK ( -- ) S FIG
Issue an error message and abort if a stack underflow or overflow
occurs. Data, return and floating point stack (if present) are
tested.
Note: A non-System version of ?STACK is provided in MISC.SCR for
turnkey applications requiring run-time stack checking.
BAL ( -- a-addr ) S
A VARIABLE containing the current control structure balance level.
Note: This replaces +BAL -BAL which incremented/decremented the
value in BAL respectively.
CHECKING ( -- a-addr ) S
A VARIABLE that controls compiler security - including control
structure balance, data stack level and protected dictionary.
If the contents are zero, checking is disabled. Default is
CHECKING ON.
See ?BAL ?CSP BEHEAD FORGET
CSP ( -- a-addr ) S FIG
A 2VARIABLE . The first cell contains the current data stack
pointer saved by !CSP . The second cell (not FIG compatible)
contains the current control-flow stack base address.
See !CSP
SMUDGE ( -- ) S FIG
Toggle the 'smudge' bit in the header of the last defined word.
If the smudge bit is set, the definition will not be found during
a dictionary search.
14. Control Flow
----------------
In DX-Forth the control-flow stack is implemented on the data stack.
Extension words CS-DROP CS-PUSH CS-POP CS-MARK CS-TEST are available
when the 'cfs' equate in the kernel source is enabled. See MISER.SCR
for example of use.
<MARK ( C: -- dest ) S 83
This function is not provided. In DX-Forth use POSTPONE BEGIN
instead.
<RESOLVE ( C: dest -- ) S 83
Compile a backward branch address in the dictionary using the
location left by BEGIN . Formerly named BACK .
>MARK ( C: -- orig ) S 83
Reserve space in the dictionary for a forward branch address
to be later resolved by THEN . Formerly named FORWARD .
>RESOLVE ( C: orig -- ) S 83
This function is not provided. In DX-Forth use POSTPONE THEN
instead.
AHEAD ( C: -- orig ) S 94
Put the location of a new unresolved forward reference orig
onto the control flow stack. Similar to IF but compiles an
unconditional forward branch.
CS-PICK ( C: xu..x0 -- xu..x0 xu ) ( S: u -- ) S 94
Remove u. Place a copy of item xu on top of the control-flow
stack.
CS-ROLL ( C: xu..x0 -- xu-1..x0 xu ) ( S: u -- ) S 94
Remove u. Rotate item xu to the top of the control-flow stack.
CS-DROP ( C: x -- ) S
Remove the top item from the control-flow stack.
CS-PUSH ( C: xu..x1 x0 -- x0 xu..x1 ) S
Rotate items on the control-flow stack such that the top item
becomes the bottom. An ambiguous condition exists if the control-
flow stack is empty before CS-PUSH is executed.
CS-POP ( C: xu xu-1..x0 -- xu-1..x0 xu ) S
Rotate items on the control-flow stack such that the bottom item
becomes the top. An ambiguous condition exists if the control-
flow stack is empty before CS-POP is executed.
CS-MARK ( C: -- x ) S
Place a marker on the control-flow stack. A marker occupies the
same width as an orig|dest but is distinguishable using CS-TEST.
CS-TEST ( C: x -- x ) ( S: -- flag ) S
Return a true flag if x is an orig|dest, or false if a marker.
x is not altered or removed.
If the control-flow stack is implemented using the data stack,
flag shall be the topmost item on the data stack.
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