NAME¶
bwbasic - Bywater BASIC interpreter/shell
Bywater BASIC Interpreter/Shell, version 2.10
---------------------------------------------
Copyright (c) 1993, Ted A. Campbell
for bwBASIC version 2.10, 11 October 1993
CONTENTS:
1. DESCRIPTION
2. TERMS OF USE
3. QUICK REFERENCE LIST OF COMMANDS AND FUNCTIONS
4. GENERAL NOTES ON USAGE
5. EXPANDED REFERENCE FOR COMMANDS AND FUNCTIONS
6. PREDEFINED VARIABLES
7. UNIMPLEMENTED COMMANDS AND FUNCTIONS
and AGENDA FOR DEVELOPMENT
8. THE STORY OF BYWATER BASIC
9. COMMUNICATIONS
The author wishes to express his thanks to Mr. David MacKenzie,
who assisted in the development Unix installation and configuration
for this version.
1. DESCRIPTION
The Bywater BASIC Interpreter (bwBASIC) implements a large
superset of the ANSI Standard for Minimal BASIC (X3.60-1978)
and a significant subset of the ANSI Standard for Full BASIC
(X3.113-1987) in C. It also offers shell programming facilities
as an extension of BASIC. bwBASIC seeks to be as portable
as possible.
bwBASIC can be configured to emulate features, commands, and
functions available on different types of BASIC interpreters;
see the file INSTALL for further installation information.
The interpreter is fairly slow. Whenever faced with a choice
between conceptual clarity and speed, I have consistently chosen
the former. The interpreter is the simplest design available,
and utilizes no system of intermediate code, which would speed
up considerably its operation. As it is, each line is interpreted
afresh as the interpreter comes to it.
bwBASIC implements one feature not available in previous BASIC
interpreters: a shell command can be entered interactively at the
bwBASIC prompt, and the interpreter will execute it under a
command shell. For instance, the command "dir *.bas" can be
entered in bwBASIC (under DOS, or "ls -l *.bas" under UNIX) and
it will be executed as from the operating system command line.
Shell commands can also be given on numbered lines in a bwBASIC
program, so that bwBASIC can be used as a shell programming
language. bwBASIC's implementation of the RMDIR, CHDIR, MKDIR,
NAME, KILL, ENVIRON, and ENVIRON$() commands and functions
offer further shell-processing capabilities.
2. TERMS OF USE:
This version of Bywater BASIC is released under the terms of the
GNU General Public License (GPL), which is distributed with this
software in the file "COPYING". The GPL specifies the terms
under which users may copy and use the software in this distribution.
A separate license is available for commercial distribution,
for information on which you should contact the author.
3. QUICK REFERENCE LIST OF COMMANDS AND FUNCTIONS
Be aware that many of these commands and functions will not be
available unless you have set certain flags in the header files
(see the expanded reference section below for dependencies).
ABS( number )
ASC( string$ )
ATN( number )
CALL subroutine-name
CASE ELSE | IF partial-expression | constant
CHAIN [MERGE] file-name [, line-number] [, ALL]
CHDIR pathname
CHR$( number )
CINT( number )
CLEAR
CLOSE [[#]file-number]...
CLS
COMMON variable [, variable...]
COS( number )
CSNG( number )
CVD( string$ )
CVI( string$ )
CVS( string$ )
DATA constant[,constant]...
DATE$
DEF FNname(arg...)] = expression
DEFDBL letter[-letter](, letter[-letter])...
DEFINT letter[-letter](, letter[-letter])...
DEFSNG letter[-letter](, letter[-letter])...
DEFSTR letter[-letter](, letter[-letter])...
DELETE line[-line]
DIM variable(elements...)[variable(elements...)]...
DO NUM|UNNUM
DO [WHILE expression]
EDIT
ELSE
ELSEIF
END IF | FUNCTION | SELECT | SUB
ENVIRON variable-string = string
ENVIRON$( variable-string )
EOF( device-number )
ERASE variable[, variable]...
ERL
ERR
ERROR number
EXP( number )
FIELD [#] device-number, number AS string-variable [, number AS string-variable...]
FILES filespec$
FUNCTION
FOR counter = start TO finish [STEP increment]
GET [#] device-number [, record-number]
GOSUB line | label
GOTO line | label
HEX$( number )
IF expression THEN [statement [ELSE statement]]
INKEY$
INPUT [# device-number]|[;]["prompt string";]list of variables
INSTR( [start-position,] string-searched$, string-pattern$ )
INT( number )
KILL file-name
LEFT$( string$, number-of-spaces )
LEN( string$ )
LET variable = expression
LINE INPUT [[#] device-number,]["prompt string";] string-variable$
LIST line[-line]
LOAD file-name
LOC( device-number )
LOCATE line, column
LOF( device-number )
LOG( number )
LOOP [UNTIL expression]
LSET string-variable$ = expression
MERGE file-name
MID$( string$, start-position-in-string[, number-of-spaces ] )
MKD$( number )
MKDIR pathname
MKI$( number )
MKS$( number )
NAME old-file-name AS new-file-name
NEW
NEXT [counter]
OCT$( number )
ON variable GOTO|GOSUB line[,line,line,...]
ON ERROR GOSUB line
OPEN "O"|"I"|"R", [#]device-number, file-name [,record length]
file-name FOR INPUT|OUTPUT|APPEND AS [#]device-number [LEN = record-length]
OPTION BASE number
POS
PRINT [# device-number,][USING format-string$;] expressions...
PUT [#] device-number [, record-number]
QUIT
RANDOMIZE number
READ variable[, variable]...
REM string
RESTORE line
RETURN
RIGHT$( string$, number-of-spaces )
RMDIR pathname
RND( number )
RSET string-variable$ = expression
RUN [line][file-name]
SAVE file-name
SELECT CASE expression
SGN( number )
SIN( number )
SPACE$( number )
SPC( number )
SQR( number )
STOP
STR$( number )
STRING$( number, ascii-value|string$ )
SUB subroutine-name
SWAP variable, variable
SYSTEM
TAB( number )
TAN( number )
TIME$
TIMER
TROFF
TRON
VAL( string$ )
WEND
WHILE expression
WIDTH [# device-number,] number
WRITE [# device-number,] element [, element ]....
4. GENERAL NOTES ON USAGE:
4.a. Interactive Environment
An interactive environment is provided if the flag INTERACTIVE
is defined as TRUE in bwbasic.h, so that a line with a
line number can be entered at the bwBASIC prompt and it will be
added to the program in memory.
Line numbers are not strictly required, but are useful if the
interactive environment is used for programming. For longer
program entry one might prefer to use an ASCII text editor, and
in this case lines can be entered without numbers. One can use
DO NUM and DO UNNUM to number or unnumber lines. See also the
documentation below for the pseudo-command EDIT.
4.b. Naming Conventions
Command names and function names are not case sensitive,
so that "Run" and "RUN" and "run" are equivalent and "abs()"
and "ABS()" and "Abs()" are equivalent. HOWEVER, variable
names ARE case sensitive in bwbASIC, so that "d$" and "D$"
are different variables. This differs from some BASIC
implementations where variable names are not case sensitive.
Variable names can use any alphabetic characters, the period
and underscore characters and decimal digits (but not in the
first position). They can be terminated with '#' or '!' to
allow Microsoft-type names, even though the precision is
irrelevant to bwBASIC.
4.c. Numerical Constants
Numerical constants may begin with a digit 0-9 (decimal), with
the "&H" or "&h" (hexadecimal) or the "&o" or "&O" (octal).
Decimal numbers may terminated with 'E', 'e', 'D', or 'd'
followed by an exponent number to denote exponential notation.
Decimal constants may also be terminated by the '#' or '!'
to comply with Microsoft-style precision terminators, although
the precision specified will be irrelevant to bwBASIC.
4.d. Command-Line Execution
A filename can be specified on the command line and will be
LOADed and RUN immediately, so that the command line
bwbasic prog.bas
will load and execute "prog.bas".
4.e. Program Storage
All programs are stored as ASCII text files.
4.f. TRUE and FALSE
TRUE is defined as -1 and FALSE is defined as 0 in the default
distribution of bwBASIC. These definitions can be changed by
those compiling bwBASIC (see file BWBASIC.H).
4.g. Assignments
Assignment must be made to variables. This differs from some
implementations of BASIC where assignment can be made to a
function. Implication: "INSTR( 3, x$, y$ ) = z$" will not
work under bwBASIC.
4.h. Operators and Precedence
bwBASIC recognizes the following operators, with their level
of precedence given (1 = highest):
^ 1 exponentiation
* 2 multiplication
/ 2 division
3 integer division
+ 5 addition
- 5 subtraction
= 6 equality or assignment
MOD 4 modulus (remainder) arithmetic
<> 7 inequality
< 8 less than
> 9 greater than
<= 10 less than or equal to
=< 10 less than or equal to
>= 11 greater than or equal to
=> 11 greater than or equal to
NOT 12 negation
AND 13 conjunction
OR 14 disjunction
XOR 15 exclusive or
IMP 16 implication
EQV 17 equivalence
4.h. Numerical Precision (NOT)
bwBASIC utilizes numbers with only one level of precision. If
the flag NUMBER_DOUBLE is defined as TRUE in bwbasic.h, the
precision implemented will be that of the C "double" data type;
otherwise (default) the precision will be that of the C "float"
type. At a number of points there are commands (or pseudo-
commands) that seem to recognize Microsoft-style precision
distinctions, but for the most part these are just work-around
aliases to allow Microsoft-style programs to be run.
5. EXPANDED REFERENCE FOR COMMANDS AND FUNCTIONS
The "Dependencies" listed in the following reference materials
refers to flags that must be set to TRUE in bwbasic.h for the
associated command or function to be implemented. These flags
are as follows:
(core) Commands and Functions in any implementation of
bwBASIC; these are the ANSI Minimal BASIC core
INTERACTIVE Commands supporting the interactive programming
environment
COMMON_CMDS Commands beyond ANSI Minimal BASIC which are common
to Full ANSI BASIC and Microsoft BASICs
COMMON_FUNCS Functions beyond the ANSI Minimal BASIC core, but
common to both ANSI Full BASIC and Microsoft-style
BASIC varieties
UNIX_CMDS Commands which require Unix-style directory and
environment routines not specified in C
STRUCT_CMDS Commands related to structured programming; all
of these are part of the Full ANSI BASIC standard
ANSI_FUNCS Functions unique to ANSI Full BASIC
MS_CMDS Commands unique to Microsoft BASICs
MS_FUNCS Functions unique to Microsoft BASICs
------------------------------------------
Function: ABS( number )
Description: ABS returns the absolute value of the argument 'number'.
Dependencies: (core)
------------------------------------------
Function: ASC( string$ )
Description: ASC returns the ASCII code for the first letter in
the argument string$.
Dependencies: MS_FUNCS
------------------------------------------
Function: ATN( number )
Description: ATN returns the arctangent value of the argument 'number'
in radians.
Dependencies: (core)
------------------------------------------
Command: CALL subroutine-name
Description: CALL calls a named subroutine (see SUB and END SUB).
Dependencies: STRUCT_CMDS
------------------------------------------
Command: CASE ELSE | IF partial-expression | constant
Description: CASE introduces an element of a SELECT CASE statement
(see SELECT CASE). CASE IF introduces a conditional
SELECT CASE element, and CASE ELSE introduces a
default SELECT CASE element.
Dependencies: STRUCT_CMDS
------------------------------------------
Command: CHAIN [MERGE] file-name [, line-number] [, ALL]
Description: CHAIN passes control to another BASIC program.
Variables declared COMMON (q.v.) will be passed
to the new program.
Dependencies: COMMON_CMDS
------------------------------------------
Command: CHDIR pathname$
Description: CHDIR changes the current directory to that indicated
by the argument pathname$.
Dependencies: UNIX_CMDS
------------------------------------------
Function: CHR$( number )
Description: CHR$ returns a one-character string with the character
corresponding to the ASCII code indicated by argument
'number'.
Dependencies: COMMON_FUNCS
------------------------------------------
Function: CINT( number )
Description: CINT returns the truncated integer for the argument
'number'.
Dependencies: MS_FUNCS
------------------------------------------
Command: CLEAR
Description: CLEAR sets all numerical variables to 0, and all
string variables to null.
Dependencies: COMMON_CMDS
------------------------------------------
Command: CLOSE [[#]file-number]...
Description: CLOSE closes the file indicated by file-number
(see OPEN).
Dependencies: COMMON_CMDS
------------------------------------------
Command: CLS
Description: CLS clears the display screen (IBM and compatibles
only as of version 2.10).
Dependencies: IMP_IQC and IMP_CMDLOC
------------------------------------------
Command: CMDS
Description: CMDS is a debugging command that prints a list
of all implemented bwBASIC commands.
Dependencies: DEBUG
------------------------------------------
Command: COMMON variable [, variable...]
Description: COMMON designates variables to be passed to a CHAINed
program (see CHAIN).
Dependencies: COMMON_CMDS
------------------------------------------
Function: COS( number )
Description: COS returns the cosine of the argument 'number'
in radians.
Dependencies: (core)
------------------------------------------
Function: CSNG( number )
Description: CSNG is a pseudo-function that has no effect under
bwBASIC. It replicates a Microsoft-type command
that would convert the 'number' to single-precision.
Dependencies: MS_FUNCS
------------------------------------------
Function: CVD( string$ )
Description: CVD converts the argument string$ into a bwBASIC
number (precision is irrelevant in bwBASIC since
bwBASIC numbers have only one precision).
Implementation-Specific Notes:
CVD(), CVI(), CVS(), MKI$(), MKD$(), MKS$(): These functions
are implemented, but are dependent on a) the sizes for integer,
float, and double values on particular systems, and b) how
particular versions of C store these numerical values. The
implication is that data files created using these functions
on a DOS-based microcomputer may not be translated correctly
by bwBASIC running on a Unix-based computer. Similarly, data
files created by bwBASIC compiled by one version of C may not be
readable by bwBASIC compiled by another version of C (even under
the same operating system). So be careful with these.
Dependencies: MS_FUNCS
------------------------------------------
Function: CVI( string$ )
Description: CVI converts the argument string$ into a bwBASIC
number (precision is irrelevant in bwBASIC since
bwBASIC numbers have only one precision; see also
the note on CVD).
Dependencies: MS_FUNCS
------------------------------------------
Function: CVS( string$ )
Description: CVI converts the argument string$ into a bwBASIC
number (precision is irrelevant in bwBASIC since
bwBASIC numbers have only one precision; see also
the note on CVD).
Dependencies: MS_FUNCS
------------------------------------------
Command: DATA constant[,constant]...
Description: DATA stores numerical and string constants to be
accessed by READ (q.v.).
Dependencies: (core)
------------------------------------------
Function: DATE$
Description: DATE$ returns the current date based on the computer's
internal clock as a string in the form "YYYY-MM-DD".
As implemented under bwBASIC, DATE$ cannot be used for
assignment (i.e., to set the system date).
Note: bwBASIC presently (v2.10) does not allow assignment
to a function.
Dependencies: COMMON_FUNCS
------------------------------------------
Command: DEF FNname(arg...)] = expression
Description: DEF defines a user-written function. This function
corresponds to Microsoft-type implementation, although
in bwBASIC DEF is a working equivalent of FUNCTION.
Dependencies: (core)
------------------------------------------
Command: DEFDBL letter[-letter](, letter[-letter])...
Description: DEFDBL declares variables with single-letter names
as numerical variables (precision is irrelevant in
bwBASIC).
Dependencies: MS_CMDS
------------------------------------------
Command: DEFINT letter[-letter](, letter[-letter])...
Description: DEFINT declares variables with single-letter names
as numerical variables (precision is irrelevant in
bwBASIC).
Dependencies: MS_CMDS
------------------------------------------
Command: DEFSNG letter[-letter](, letter[-letter])...
Description: DEFSNG declares variables with single-letter names
as numerical variables (precision is irrelevant in
bwBASIC).
Dependencies: MS_CMDS
------------------------------------------
Command: DEFSTR letter[-letter](, letter[-letter])...
Description: DEFSTR declares variables with single-letter names
as string variables.
Dependencies: MS_CMDS
------------------------------------------
Command: DELETE line[-line]
Description: DELETE deletes program lines indicated by the
argument(s). If you want to use DELETE for non-
numbered programs, first use DO NUM, then DELETE,
then DO UNNUM.
Dependencies: INTERACTIVE
------------------------------------------
Command: DIM variable(elements...)[variable(elements...)]...
Description: DIM specifies variables that have more than one
element in a single dimension, i.e., arrayed
variables.
Note: As implemented under bwBASIC, DIM accepts only
parentheses as delimiters for variable fields.
(Some BASICs allow the use of square brackets.)
Dependencies: (core)
------------------------------------------
Command: DO NUM|UNNUM
Description: DO NUM numbers all lines in a program. The first
line is given the number 10, and subsequent lines
are numbered consecutively in multiples of 10. DO
UNNUM removes all line numbers from a program.
NOTE that these functions do nothing to line
numbers, e.g., following a GOSUB or GOTO statement;
these commands cannot be used as a replacement for
RENUM (available in some systems, but not bwBASIC).
With these commands, however, one can develop
unnumbered programs by entering new lines with numbers,
then running DO UNNUM to remove the line numbers.
Together with LOAD and SAVE (q.v.) one can use
bwBASIC as a primitive text editor.
Dependencies: INTERACTIVE
------------------------------------------
Command: DO [WHILE expression]
Description: DO implements a number of forms of program loops.
DO...LOOP simply loops; the only way out is by
EXIT; DO WHILE...LOOP loops while "expression" is
true (this is equivalent to the older WHILE-WEND
loop, also implemented in bwBASIC); DO...LOOP UNTIL
loops until the expression following UNTIL is true.
Dependencies: STRUCT_CMDS
------------------------------------------
Command: EDIT
Description: EDIT is a pseudo-command which calls the text editor
specified in the variable BWB.EDITOR$ to edit the
program in memory. After the call to the text editor,
the (edited) program is reloaded into memory. The user
normally must specific a valid path and filename in
BWB.EDITOR$ before this command will be useful.
Dependencies: COMMON_CMDS
------------------------------------------
Command: ELSE
Description: ELSE introduces a default condition in a multi-line IF
statement.
Dependencies: STRUCT_CMDS
------------------------------------------
Command: ELSEIF
Description: ELSEIF introduces a secondary condition in a multi-
line IF statement.
Dependencies: STRUCT_CMDS
------------------------------------------
Command: END IF | FUNCTION | SELECT | SUB
Description: END IF ends a multi-line IF statement. END FUNCTION
ends a multi-line function definition. END SELECT
ends a SELECT CASE statement. END SUB ends a multi-
line subroutine definition.
Dependencies: STRUCT_CMDS
------------------------------------------
Command: ENVIRON variable-string$ = string$
Description: ENVIRON sets the environment variable identified by
variable-string$ to string$.
It might be noted that this differs from the implementation
of ENVIRON in some versions of BASIC, but bwBASIC's ENVIRON
allows BASIC variables to be used on either side of the equals
sign. Note that the function ENVIRON$() is different from the
command, and be aware of the fact that in some operating systems
an environment variable set within a program will not be passed
to its parent shell.
Dependencies: UNIX_CMDS
------------------------------------------
Function: ENVIRON$( variable-string$ )
Description: ENVIRON$ returns the environment variable associated with
the name variable-string$.
Dependencies: MS_FUNCS
------------------------------------------
Function: EOF( device-number )
Description: EOF returns TRUE (-1) if the device associated with
device-number is at the end-of-file, otherwise it
returns FALSE (0).
Dependencies: MS_FUNCS
------------------------------------------
Command: ERASE variable[, variable]...
Description: ERASE eliminates arrayed variables from a program.
Dependencies: COMMON_CMDS
------------------------------------------
Function: ERL
Description: ERL returns the line number of the most recent error.
Dependencies: MS_FUNCS
------------------------------------------
Function: ERR
Description: ERR returns the error number of the most recent error.
Note that if PROG_ERRORS has been defined when bwBASIC is
compiled, the ERR variable will not be set correctly upon
errors. It only works when standard error messages are used.
Dependencies: MS_FUNCS
------------------------------------------
Command: ERROR number
Description: ERROR simulates an error, i.e., displays the message
appropriate for that error. This command is helpful
in writing ON ERROR GOSUB routines that can identify
a few errors for special treatment and then ERROR ERR
(i.e., default handling) for all others.
Dependencies: COMMON_CMDS
------------------------------------------
Command: EXIT [FOR]
Description: EXIT by itself exits from a DO...LOOP loop;
EXIT FOR exits from a FOR...NEXT loop.
Dependencies: STRUCT_CMDS
------------------------------------------
Function: EXP( number )
Description: EXP returns the exponential value of 'number'.
Dependencies: (core)
------------------------------------------
Command: FIELD [#] device-number, number AS string-variable$ [, number AS string-variable$...]
Description: FIELD allocates space in a random file buffer for device
indicated by device-number, allocating 'number' bytes
and assigning the bytes at this position to the variable
string-variable$.
Dependencies: COMMON_CMDS
------------------------------------------
Command: FILES filespec$
Description: FILES is a pseudocommand that invokes the directory program
specified in the variable BWB.FILES$ with the argument
filespec$. Normally, the user must set this variable
before FILES can be used. E.g., for PC-type computers,
BWB.FILES$ = "DIR"
will work, for Unix machines,
BWB.FILES$ = "ls -l"
etc.
Dependencies: COMMON_CMDS
------------------------------------------
Command: FNCS
Description: CMDS is a debugging command that prints a list
of all pre-defined bwBASIC functions.
Dependencies: DEBUG
------------------------------------------
Command: FUNCTION
Description: FUNCTION introduces a function definition, normally
ending with END FUNCTION. In bwBASIC, FUNCTION and
DEF are working equivalents, so either can be used
with single-line function definitions or with multi-
line definitions terminated by END FUNCTION.
Dependencies: STRUCT_CMDS
------------------------------------------
Command: FOR counter = start TO finish [STEP increment]
Description: FOR initiates a FOR-NEXT loop with the variable
'counter' initially set to 'start' and incrementing
in 'increment' steps (default is 1) until 'counter'
equals 'finish'.
Dependencies: (core)
------------------------------------------
Command: GET [#] device-number [, record-number]
Description: GET reads the next record from a random-access file
or device into the buffer associated with that file.
If record-number is specified, the GET command reads the
specified record.
Dependencies: COMMON_CMDS
------------------------------------------
Command: GOSUB line | label
Description: GOSUB initiates a subroutine call to the line (or label)
specified. The subroutine must end with RETURN.
Dependencies: (core), but STRUCT_CMDS for labels
------------------------------------------
Command: GOTO line | label
Description: GOTO branches program execution to the specified line
(or label).
Dependencies: (core), but STRUCT_CMDS for labels
------------------------------------------
Function: HEX$( number )
Description: HEX$ returns a string giving the hexadecimal (base 16)
value for the 'number'.
Dependencies: MS_FUNCS
------------------------------------------
Command: IF expression THEN [statement [ELSE statement]]
Description: IF evaluates 'expression' and performs the THEN
statement if it is true or (optionally) the
ELSE statement if it is FALSE. If STRUCT_CMDS
is set to TRUE, bwBASIC allows multi-line IF
statements with ELSE and ELSEIF cases, ending
with END IF.
Dependencies: (core), STRUCT_CMDS for multi-line IF statements
------------------------------------------
Function: INKEY$
Description: INKEY$ reads the status of the keyboard, and a single
keypress, if available. If a keypress is not available,
then INKEY$ immediately returns a null string ("").
Currently (v2.10) implemented in bwx_iqc.c only.
Dependencies: IMP_IQC and IMP_CMDLOC
------------------------------------------
Command: INPUT [# device-number]|[;]["prompt string";]list of variables
Description: INPUT allows input from the terminal or a device
specified by device-number. If terminal, the "prompt
string" is output, and input is assigned to the
appropriate variables specified.
bwBASIC does not support the optional feature of INPUT
that suppresses the carriage-return and line-feed at the end
of the input. This is because C alone does not provide for any
means of input other than CR-LF-terminated strings.
Dependencies: (core)
------------------------------------------
Function: INSTR( [start-position,] string-searched$, string-pattern$ )
Description: INSTR returns the position at which string-pattern$
occurs in string-searched$, beginning at start-position.
As implemented in bwBASIC, INSTR cannot be used for
assignments.
Note: bwBASIC presently (v2.10) does not allow assignment
to a function.
Dependencies: MS_FUNCS
------------------------------------------
Function: INT( number )
Description: INT returns the largest integer less than or equal to
the argument 'number'. NOTE that this is not a "truncated"
integer function, for which see CINT.
Dependencies: (core)
------------------------------------------
Command: KILL file-name$
Description: KILL deletes the file specified by file-name$.
Dependencies: UNIX_CMDS
------------------------------------------
Function: LEFT$( string$, number-of-spaces )
Description: LEFT$ returns a substring a string$ with number-of-spaces
from the left (beginning) of the string). As implemented
under bwBASIC, it cannot be used for assignment.
Dependencies: MS_FUNCS
------------------------------------------
Function: LEN( string$ )
Description: LEN returns the length in bytes of string$.
Dependencies: COMMON_FUNCS
------------------------------------------
Command: LET variable = expression
Description: LET assigns the value of 'expression' to the variable.
As currently implemented, bwBASIC supports implied LET
statements (e.g., "X = 4.5678" at the beginning of
a line or line segment, but does not support assignment
to multiple variables (e.g., "x, y, z = 3.141596").
Dependencies: (core)
------------------------------------------
Command: LINE INPUT [[#] device-number,]["prompt string";] string-variable$
Description: LINE INPUT reads entire line from the keyboard or a file
or device into string-variable$. If input is from the
keyboard (stdin), then "prompt string" will be printed
first. Unlike INPUT, LINE INPUT reads a whole line,
not stopping for comma-delimited data items.
Dependencies: COMMON_CMDS
------------------------------------------
Command: LIST line[-line]
Description: LIST lists program lines as specified in its argument.
Dependencies: INTERACTIVE
------------------------------------------
Command: LOAD file-name
Description: LOAD loads an ASCII BASIC program into memory.
Dependencies: INTERACTIVE
------------------------------------------
Function: LOC( device-number )
Description: LOC returns the next record that GET or PUT statements
will use.
Dependencies: MS_FUNCS
------------------------------------------
Command: LOCATE line, column
Description: LOCATE addresses trhe curor to a specified line and
column. Currently (v2.10) implemented in bwx_iqc.c only.
Dependencies: IMP_IQC and IMP_CMDLOC
------------------------------------------
Function: LOF( device-number )
Description: LOF returns the length of a file (specified by device-number)
in bytes.
Dependencies: MS_FUNCS
------------------------------------------
Function: LOG( number )
Description: LOG returns the natural logarithm of the argument 'number'.
Dependencies: (core)
------------------------------------------
Command: LOOP [UNTIL expression]
Description: LOOP terminates a program loop: see DO.
Dependencies: STRUCT_CMDS
------------------------------------------
Command: LSET string-variable$ = expression
Description: LSET transfers data from 'expression' to the left-hand
side of a string variable or random access buffer field.
Dependencies: COMMON_CMDS
------------------------------------------
Command: MERGE file-name
Description: MERGE adds program lines from 'file-name' to the program
in memory. Unlike LOAD, it does not clear the program
currently in memory.
Dependencies: COMMON_CMDS
------------------------------------------
Function: MID$( string$, start-position-in-string[, number-of-spaces ] )
Description: MID$ returns a substring of string$ beginning at
start-position-in-string and continuing for
number-of-spaces bytes.
Dependencies: MS_FUNCS
------------------------------------------
Command: MKDIR pathname$
Description: MKDIR creates a new directory path as specified by
pathname$.
Dependencies: UNIX_CMDS
------------------------------------------
Function: MKD$( number )
Description: MKD$, MKI$, and MKS$ are all equivalent in bwBASIC.
They convert the numerical value 'number' into a string
which can be stored in a more compressed form in a file
(especially for random file access). Since bwBASIC does
not recognize differences in precision, these commands
are effectively equivalent.
Dependencies: MS_FUNCS
------------------------------------------
Function: MKI$( number )
Description: Equivalent to MKD$ (q.v.)
Dependencies: MS_FUNCS
------------------------------------------
Function: MKS$( number )
Description: Equivalent to MKD$ (q.v.).
Dependencies: MS_FUNCS
------------------------------------------
Command: NAME old-file-name AS new-file-name
Description: NAME renames an existing file (old-file-name) as
new-file-name.
Dependencies: UNIX_CMDS
------------------------------------------
Command: NEW
Description: NEW deletes the program in memory and clears all
variables.
Dependencies: INTERACTIVE
------------------------------------------
Command: NEXT [counter-variable]
Description: NEXT comes at the end of a FOR-NEXT loop; see FOR.
Dependencies: (core)
------------------------------------------
Function: OCT$( number )
Description: OCT$ returns a string giving the octal (base 8)
representation of 'number'.
Dependencies: MS_FUNCS
------------------------------------------
Command: ON variable GOTO|GOSUB line[,line,line,...]
Description: ON either branches (GOTO) or calls a subroutine
(GOSUB) based on the rounded value of variable;
if it is 1, the first line is called, if 2, the second
line is called, etc.
Dependencies: (core)
------------------------------------------
Command: ON ERROR GOSUB line|label
Description: ON ERROR sets up an error handling subroutine. See
also ERROR.
Dependencies: COMMON_CMDS, STRUCT_CMDS for labels
------------------------------------------
Command: OPEN "O"|"I"|"R", [#]device-number, file-name [,record length]
file-name FOR INPUT|OUTPUT|APPEND AS [#]device-number [LEN = record-length]
Description: OPEN allocates random access memory for access to a disk
file or other device. Note that two quite different forms
of the OPEN statement are supported. In the first form,
"O" (note that these letters must be encased in quotation
marks) denotes sequential output, "I" denotes sequential
input, and "R" denotes random-access input and output.
Once OPEN, any number of operations can be performed
on a device (see WRITE #, INPUT #, PRINT #, etc.).
Dependencies: COMMON_CMDS
------------------------------------------
Command: OPTION BASE number
Description: OPTION BASE sets the lowest value for array subscripts,
either 0 or 1.
Dependencies: (core)
------------------------------------------
Function: POS
Description: POS returns the current cursor position in the line.
Dependencies: COMMON_FUNCS
------------------------------------------
Command: PRINT [# device-number,][USING format-string$;] expressions...
Description: PRINT outputs text to the screen or to a file or device
specified by device-number. In the current implementation
of bwBASIC, expressions to be printed must be separated by
the comma (tabbed output), the semicolon (immediate
sequential output) or the plus sign (immediate sequential
output by string concatenation). Expressions separated
by blanks or tabs are not supported. If USING is specified,
a number of formatting marks may appear in the format
string:
! prints the first character of a string
\ prints 2+x characters of a string, where x =
the number of spaces between the backslashes
& variable-length string field
# represents a single digit in output format for
a number
. decimal point in a number
+ sign of a number (will output + or -)
- trailing minus after a number
** fill leading spaces with asterisks
$$ output dollar sign in front of a number
^^ output number in exponential format
_ output next character literally
As currently implemented, the exponential format
will be that used by the C compiler.
Dependencies: (core), COMMON_FUNCS for USING
------------------------------------------
Command: PUT [#] device-number [, record-number]
Description: PUT outputs the next available record or the record
specified by record-number to the file or device
denoted by device-number.
Dependencies: COMMON_CMDS
------------------------------------------
Command: QUIT
Description: QUIT is a synonym for SYSTEM; with INTERACTIVE
environment, it exits the program to the
operating system (or the calling program).
Dependencies: INTERACTIVE
------------------------------------------
Command: RANDOMIZE number
Description: RANDOMIZE seeds the random number generator (see RND).
Under bwBASIC, the TIMER function (q.v.) can be used
to supply a 'number' seed for the random number
generator.
Dependencies: (core)
------------------------------------------
Command: READ variable[, variable]...
Description: READ reads values from DATA statements and assigns these
values to the named variables. Variable types in a READ
statement must match the data types in DATA statements
as they are occurred. See also DATA and RESTORE.
Dependencies: (core)
------------------------------------------
Command: REM string
Description: REM allows remarks to be included in a program. As
currently implemented, the entire line following
REM is ignored by the interpreter (thus, even if
MULTISEG_LINES is set, a REM line will not be able
to find a segment delimiter (":") followed by another
line segment with command. bwBASIC does not currently
implement the Microsoft-style use of the single quotation
mark to denote remarks.
Dependencies: (core)
------------------------------------------
Command: RESTORE line
Description: RESTORE resets the line and position counters for DATA
and READ statements to the top of the program file or
to the beginning of the specified line. (Currently this
must be a line number.)
Dependencies: (core)
------------------------------------------
Command: RETURN
Description: RETURN concludes a subroutine called by GOSUB.
Dependencies: (core)
------------------------------------------
Function: RIGHT$( string$, number-of-spaces )
Description: RIGHT$ returns a substring a string$ with number-of-spaces
from the right (end) of the string). As implemented
under bwBASIC, it cannot be used for assignment.
Dependencies: MS_FUNCS
------------------------------------------
Command: RMDIR pathname
Description: RMDIR deletes the directory path indicated by pathname.
Dependencies: UNIX_CMDS
------------------------------------------
Function: RND( number )
Description: RND returns a pseudo-random number. The 'number' value
is ignored by bwBASIC if supplied. The RANDOMIZE
command (q.v.) reseeds the random-number generator.
Dependencies: (core)
------------------------------------------
Command: RSET string-variable$ = expression
Description: RSET transfers data from 'expression' to the right-hand
side of a string variable or random access buffer field.
Dependencies: COMMON_CMDS
------------------------------------------
Command: RUN [line][file-name$]
Description: RUN executes the program in memory. If a file-name$ is
supplied, then the specified file is loaded into memory
and executed. If a line number is supplied, then execution
begins at that line.
Dependencies: INTERACTIVE
------------------------------------------
Command: SAVE file-name$
Description: SAVE saves the program in memory to file-name$. bwBASIC
only saves files in ASCII format.
Dependencies: INTERACTIVE
------------------------------------------
Command: SELECT CASE expression
Description: SELECT CASE introduces a multi-line conditional selection
statement. The expression given as the argument to SELECT
CASE will be evaluated by CASE statements following. The
SELECT CASE statement concludes with an END SELECT
statement.
As currently implemented, CASE statements may be followed
by string values, but in this case only simple comparisons
(equals, not equals) can be performed.
Dependencies: STRUCT_CMDS
------------------------------------------
Function: SGN( number )
Description: SGN returns the sign of the argument 'number', +1
for positive numbers, 0 for 0, and -1 for negative numbers.
Dependencies: (core)
------------------------------------------
Function: SIN( number )
Description: SIN returns the sine of the argument 'number'
in radians.
Dependencies: (core)
------------------------------------------
Function: SPACE$( number )
Description: SPACE$ returns a string of blank spaces 'number'
bytes long.
Dependencies: MS_FUNCS
------------------------------------------
Function: SPC( number )
Description: SPC returns a string of blank spaces 'number'
bytes long.
Dependencies: MS_FUNCS
------------------------------------------
Function: SQR( number )
Description: SQR returns the square root of the argument 'number'.
Dependencies: (core)
------------------------------------------
Command: STOP
Description: STOP interrupts program execution. As implemented under
bwBASIC, STOP issues a SIGINT signal.
Dependencies: (core)
------------------------------------------
Function: STR$( number )
Description: STR$ returns a string giving the decimal (base 10)
representation of the argument 'number'.
Dependencies: COMMON_FUNCS
------------------------------------------
Function: STRING$( number, ascii-value|string$ )
Description: STRING$ returns a string 'number' bytes long consisting
of either the first character of string$ or the character
answering to the ASCII value ascii-value.
Dependencies: MS_FUNCS
------------------------------------------
Command: SUB subroutine-name
Description: SUB introduces a named, multi-line subroutine. The
subroutine is called by a CALL statement, and concludes
with an END SUB statement.
Dependencies: STRUCT_CMDS
------------------------------------------
Command: SWAP variable, variable
Description: SWAP swaps the values of two variables. The two variables
must be of the same type (either numerical or string).
Dependencies: COMMON_CMDS
------------------------------------------
Command: SYSTEM
Description: SYSTEM exits from bwBASIC to the calling program or
(more usually) the operating system.
Dependencies: INTERACTIVE
------------------------------------------
Function: TAB( number )
Description: TAB outputs spaces until the column indicated by
'number' has been reached.
Dependencies: (core)
------------------------------------------
Function: TAN( number )
Description: TAN returns the tangent of the argument 'number'
in radians.
Dependencies: (core)
------------------------------------------
Function: TIME$
Description: TIME$ returns the current time based on the computer's
internal clock as a string in the form "HH-MM-SS".
As implemented under bwBASIC, TIME$ cannot be used for
assignment (i.e., to set the system time).
Note: bwBASIC presently (v2.10) does not allow assignment
to a function.
Dependencies: COMMON_FUNCS
------------------------------------------
Function: TIMER
Description: TIMER returns the time in the system clock in seconds
elapsed since midnight.
Dependencies: MS_FUNCS
------------------------------------------
Command: TROFF
Description: TROFF turns of the trace facility; see TRON.
Dependencies: COMMON_CMDS
------------------------------------------
Command: TRON
Description: TRON turns on the trace facility. This facility will print
each line number in square brackets as the program is
executed. This is useful in debugging programs with
line numbers. To debug an unnumbered program with
TRON, call DO NUM first, but remember to call DO UNNUM
before you save the program later.
Dependencies: COMMON_CMDS
------------------------------------------
Function: VAL( string$ )
Description: VAL returns the numerical value of the string$.
Dependencies: COMMON_FUNCS
------------------------------------------
Command: VARS
Description: VARS is a debugging command which prints a list of
all variables defined which have global scope.
Dependencies: DEBUG
------------------------------------------
Command: WEND
Description: WEND concludes a WHILE-WEND loop; see WHILE.
Dependencies: COMMON_CMDS
------------------------------------------
Command: WHILE expression
Description: WHILE initiates a WHILE-WEND loop. The loop ends with
WEND, and execution reiterates through the loop as
long as the 'expression' is TRUE (-1).
Dependencies: COMMON_CMDS
------------------------------------------
Command: WIDTH [# device-number,] number
Description: WIDTH sets screen or device output to 'number'
columns. device-number specifies the device
or file for output.
Dependencies: COMMON_CMDS
------------------------------------------
Command: WRITE [# device-number,] element [, element ]....
Description: WRITE outputs variables to the screen or to a file
or device specified by device-number. Commas
are inserted between expressions output, and strings
are enclosed in quotation marks.
Dependencies: COMMON_CMDS
------------------------------------------
6. PREDEFINED VARIABLES
BWB.EDITOR$
BWB.FILES$
BWB.PROMPT$
BWB.IMPLEMENTATION$
The commands EDIT and FILES are pseudo-commands that launch
shell programs named in the variables BWB.EDITOR$ and BWB.FILES$,
respectively. The default values for these variables can
be changed in bwbasic.h (DEF_EDITOR and DEF_FILES), or they
can be changed on the fly by the user. An idea might be to
initialize these variables in "profile.bas" for specific
implementations; for instance, BWB.FILES$ might be defined as
"ls -l" on Unix systems or "dir" on DOS systems.
The preset variable BWB.PROMPT$ can be used to set the prompt
string for bwBASIC. Again, it is suggested that a user-
selected prompt can be set up in a "profile.bas" to be
initialized each time bwBASIC starts. Note that special
characters can be added to the prompt string, e.g.,
BWB.PROMPT$ = "Ok"+CHR$(10)
will give an "Ok" prompt followed by a linefeed.
The preset variable BWB.IMPLEMENTATION$ will return "TTY" for
the bwx_tty implementation and will return "IQC" for the
IBM PC or Compatibles with QuickC (bwx_iqc) implementation.
This may be useful in determining which commands and functions
(specifically CLS, LOCATE, and INKEY$) may be available.
7. UNIMPLEMENTED COMMANDS AND FUNCTIONS, and AGENDA FOR DEVELOPMENT
There are some items not implemented that have been so long
a part of standard BASICs that their absence will seem surprising.
In each case, though, their implementation would require opera-
ting-system-specific functions or terminal-specific functions
that cannot be universally provided. Some specific examples:
CLOAD Relies on CP/M or MSDOS conventions for binary
executable files.
CONT See RESUME below (programmer ignorance?).
DEF USR Relies on CP/M or MSDOS conventions for binary
executable files.
FRE() The ability to report the amount of free memory
remaining is system-specific due to varying patterns
of memory allocation and access; consequently this
ability is not present in ANSI or earlier versions
of C and this function is not available in bwBASIC.
INPUT$() C by itself is not able to read unechoed keyboard
input, and can read keyboard input only after a
Carriage-Return has been entered.
INP Calls to hardware ports, like machine-language
routines, are highly system-specific and cannot
be implemented in C alone.
LLIST See LPRINT below.
LPOS See LPRINT below.
LPRINT and LLIST, etc., require access to a printer device,
and this varies from one system to another. Users
might try OPENing the printer device on their own
operating system (e.g., "/dev/lp" on Unix systems,
or "PRN" under DOS) and see if printing can be done
from bwBASIC in this way.
NULL In this case, I am convinced that NULL is no longer
necessary, since very few printers now require NULLs
at the end of lines.
OUT See INP above (calls to hardware ports).
PEEK() PEEK and POKE enabled earlier BASICs to address
particular memory locations. Although bwBASIC
could possibly implement this command (POKE) and
this function (PEEK()), the limitation would be
highly limited by the different systems for
memory access in different systems.
POKE see PEEK() above.
RENUM Since unnumbered lines can be entered and
executed under bwBASIC, it would not be
possible to implement a RENUM routine.
Instead, bwBASIC uses DO NUM and DO UNNUM.
RESUME Is this possible under C? If so, I
simply have failed to figure it out yet.
Mea culpa (but not maxima).
USR See CALL and DEF USR above (machine language
subroutines).
VARPTR See PEEK and POKE above.
WAIT See INP and OUT above.
There are other commands, functions, and implementation details
that I am working on, and which are on the agenda list for future
versions of bwBASIC. These agenda include:
PARACT i.e., the ability to execute PARallel ACTions. This
is described in ANSI BASIC, although I have not seen it
implemented before. It will offer a rough, non-
preemptive form of multitasking within the scope
of a BASIC program. Programmers will note points at which
there are already hooks for PARACT in bwBASIC.
XMEM PC-type computers need to be able to use extended
memory. If we could use extended memory for program
lines, variables, and function definitions, we could
write much longer programs. This would entail,
however, a fairly serious rewriting of the program
to utilize memory handles for these storage features
instead of direct memory pointers.
Windows The addition of memory handles in addition to the
non-preemptive execution of program lines (in a
crude form, already present) will make it possible
to develop implementations for Windows and perhaps
for other graphical user interfaces. But what form
should this take? I have in mind presently a BASIC
that would run in the background, appearing only
as an icon in the GUI space, with pop-up editors
and output windows. Thus, the interpreted language
would serve a purpose something like 'cron' (a task
scheduler) under Unix systems. You may have some
reflections that would help me in this.
Graphics Here we face fairly critical differences in different
styles and implementations of graphics, e.g., between
GWBASIC, ANSI BASIC, VisualBASIC, etc. But it's
possible that Graphics commands and functions could
be added. These would all be implementation-specific.
The ANSI Standard for full BASIC does not specify which particular
commands or functions must be implemented, and in fact the standard
is very robust. Perhaps no implementation of BASIC would ever
include all of the items, but some ANSI commands and functions which
remain unimplemented are:
ACCESS
ANGLE
AREA
ARITHMETIC
ARRAY
ASK
BSTR
BVAL
CEIL
CELLS
CLIP
COLLATE
CONNECT
COSH
DATUM
DEBUG
DECIMAL
DECLARE
DEGREES
DEVICE
DISCONNECT
DISPLAY
DOT
DRAW
ERASE
EVENT
EXCEPTION
GRAPH
HANDLER
IMAGE
KEY
LCASE
LINES
LOG10
LOG2
MAT
MIX
MULTIPOINT
OUTIN
OUTPUT
PARACT
PICTURE
PIXEL
PLOT
POINTS
RADIANS
RECEIVE
RENUMBER
REWRITE
ROTATE
ROUND
SEIZE
SEND
SHIFT
SINH
TANH
TIMEOUT
TRACE
TRANSFORM
TRUNCATE
UBOUND
UCASE
VIEWPORT
WAIT
VIEWPORT
ZONEWIDTH
8. THE STORY OF BYWATER BASIC
This program was originally begun in 1982 by my grandmother, Mrs.
Verda Spell of Beaumont, TX. She was writing the program using
an ANSI C compiler on an Osborne I CP/M computer and although my
grandfather (Lockwood Spell) had bought an IBM PC with 256k of
RAM my grandmother would not use it, paraphrasing George Herbert
to the effect that "He who cannot in 64k program, cannot in 512k."
She had used Microsoft BASIC and although she had nothing against
it she said repeatedly that she didn't understand why Digital
Research didn't "sue the socks off of Microsoft" for version 1.0
of MSDOS and so I reckon that she hoped to undercut Microsoft's
entire market and eventually build a new software empire on
the North End of Beaumont. Her programming efforts were cut
tragically short when she was thrown from a Beaumont to Port
Arthur commuter train in the summer of 1986. I found the source
code to bwBASIC on a single-density Osborne diskette in her knitting
bag and eventually managed to have it all copied over to a PC
diskette. I have revised it slightly prior to this release. You
should know, though, that I myself am an historian, not a programmer.
9. COMMUNICATIONS:
email: tcamp@delphi.com
