Brandy
~~~~~~
Contents
~~~~~~~~
Introduction
Copyright
Disclaimer
Using the Interpreter
Running Programs
Programs and Libraries
Differences Between Brandy and RISC OS's Interpreter
Identifying the Environment Under Which Brandy is Running
I/O Redirection
Using Basic as a Script Language Under NetBSD and Linux
The SYS Statement
The 'key' Command
Performance
Important Error Messages
Known Problems
Miscellaneous Comments
Conclusion
Contact
Introduction
~~~~~~~~~~~~
Brandy is a Basic V interpreter. It is source code compatible with
Acorn's Basic V interpreter and runs under a number of different
operating systems. It currently works with RISC OS, NetBSD (arm32
and i386), Linux (X86) and DOS using the DJGPP DOS extender. The
aim of this project is to write a Basic interpreter that is
compatible with the Acorn interpreter and that runs identically
across all supported operating systems, emulating features of the
RISC OS environment where necessary so that a program will run
unchanged using the Acorn interpreter under RISC OS or this one
under any other OS. No attempt has been made to support features
of operating systems other than RISC OS, for example, it is not
possible to make operating system calls from within a program
except under RISC OS. The program is simply a Basic interpreter
and that is all.
These notes describe how to use the program and discuss
differences between it and Acorn's interpreter. They also detail
the extensions to Basic V that have been implemented and finish
with some miscellaneous remarks about the program and a list of
the known bugs.
Copyright
~~~~~~~~~
Brandy is copyright (C) 2000, 2001, 2002, 2003, 2004 David Daniels.
The program is distributed under the terms of the GNU GPL.
Brandy is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your
option) any later version.
Brandy is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with Brandy; see the file COPYING. If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.
Disclaimer
~~~~~~~~~~
The Brandy Basic interpreter is provided 'as is' and people using
it do so entirely at their own risk. No liability whatsoever will
be accepted for any loss or damage arising from the use of this
software.
Using the Interpreter
~~~~~~~~~~~~~~~~~~~~~
To invoke the interpreter, type:
brandy [ <options> ] [ <filename> ]
where <filename> is the optional name of the program to load and
<options> is one or more of the following:
-help Print a summary of these options.
-size <size> Set the size of the Basic workspace to
<size> bytes when starting the interpreter.
The minimum size allowed is 10000 bytes
and anything below this value will be set
to it. The maximum size is limited only
by the environment in which the program
is being run. The size may have a suffix
of 'k' to denote that the size is in
kilobytes or 'm' if it is in megabytes,
for example, '-size 100k' will set the
workspace size to 100 kilobytes (102400
bytes) and '-size 8m' will set it to
eight megabytes (8388608 bytes).
-lib <filename> Load Basic library <filename> when the
interpreter starts. This option can be
repeated as many times as required to load
a number of libraries. This is equivalent
to typing 'INSTALL <filename>' at the
interpreter's command line. The libraries
are loaded in the order given on the
command line. Note that the search order
is the reverse of this.
-load <filename> Load Basic program <filename> when the
interpreter starts.
-path <directory list> This specifies a list of directories that
the interpreter will search when looking
for libraries and programs. The directory
names are separated by commas. The pseudo-
variable 'FILEPATH$' is set to this value.
See the section below on FILEPATH$ for
more details.
-quit <filename> Load and run the Basic program <filename>.
Leave the interpreter when the program has
finished running.
-chain <filename> Load and run the Basic program <filename>.
Remain in the interpreter when the program
has finished running.
-graphics Start the interpreter with the screen in
graphics mode in versions of the program
which support graphics and the screen can
be in either text or graphics modes.
-ignore Ignore certain 'unsupported feature' errors.
By default the interpreter reports an error
whenever it comes across a Basic V feature
that it does not support. This option allows
some unsupported features that do not affect
the basic running of the program to be
ignored.
<filename> Load and run the Basic program <filename>.
Remain in the interpreter when the program
has finished running.
-nostar Do not check commands issued via OSCLI to
see if they are dealt with by Brandy. Pass
all commands to the underlying operating
system.
The case of the names of the options is ignored. It depends on the
operating system under which the interpreter is running as to
whether the names of files are case sensitive or insensitive.
Minimum Abbreviations
---------------------
Options can be abbreviated. The interpreter only checks the first
one or two characters of the option name to identify it.
-chain -c
-graphics -g
-help -h
-ignore -ig
-lib -li
-load -lo
-path -p
-quit -q
-size -s
-nostar -no
Parameters for Basic Programs
-----------------------------
The interpreter assumes that any unrecognised options are meant
to be for the Basic program and ignores them.
!!Brandy
--------
This is an obey file for RISC OS that runs Brandy in a Taskwindow.
The file can be placed on the pinboard and the interpreter started
by double clicking on it.
Running Programs
~~~~~~~~~~~~~~~~
The name of the program to run can be specified on the command
line. If no name is given, the interpreter starts with a '>'
prompt. Programs can be loaded, edited and run from here. Briefly,
the commands to use are as follows:
QUIT
Leaves the interpreter.
LOAD <filename>
Load program <filename> into the Basic workspace.
SAVE <filename>
Save the program in the Basic workspace in file <filename>.
RUN
Run the program.
LIST
LIST <line number>
LIST <line number> , <line number>
The first version lists the entire program. The second one lists
just the line supplied. The third lists lines with line numbers in
the range given.
EDIT
This transfers the program in memory to a text editor where it can
be more easily edited. The program is reloaded when the editor is
quitted.
EDIT <line number>
This copies the line specified to the command line where it can be
edited.
DELETE <line number>
DELETE <line number> , <line number>
The first version of DELETE deletes a single line from the
program, line <line number>. The second version is used to
delete a block of lines. Note that it is not possible to
recover any lines deleted.
RENUMBER
Renumbers the lines of a program.
NEW
Discard the program in the Basic workspace.
Editing Programs
----------------
Any Basic statement typed in without a line number is executed
immediately.
Basic statements typed in which start with a line number are
either added to the program or replace the line if the line number
duplicates ones already in the program.
The 'EDIT' command can be used to transfer a program into
a text editor where it can be edited more easily.
The file 'basic' contains more details of these commands and
others as well as information on Basic V.
Programs and Libraries
~~~~~~~~~~~~~~~~~~~~~~
Loading and Saving Programs
---------------------------
The interpreter can read Basic programs that have been saved as
plain text or tokenised using Acorn Basic tokens. It always stores
them as plain text. The reasons for working with text files are
that it is not a large overhead to tokenise and expand programs,
it is more portable and it allows programs to be edited with any
text editor.
Line numbers can be left out when creating a program in a text
editor. The interpreter will add them when it reads the program.
The line numbers added start at 1 and go up by 1 so that the
line numbers given in error messages match up with the lines
of the program in a text editor.
One feature of the interpreter is that it notes the name of the
file on a 'LOAD' command and uses that name if the 'SAVE' command
is used without specifying a filename. The interpreter also
supports the case where the filename is supplied on the first line
of the program. This take precedence over the name saved from the
'LOAD' command. (change?)
Libraries
---------
The interpreter supports libraries of procedures and functions
that can be loaded using either the 'INSTALL' command or the
'LIBRARY' statement in a program. Those loaded via the 'INSTALL'
command will be permanently loaded and are available until the run
of the interpreter finishes. The command line option '-lib' can be
used to specify libraries that will be 'INSTALL'ed when the
interpreter starts. Libraries loaded by the 'LIBRARY' statement
are read at the time the statement is encountered and will be
discarded when a further RUN statement is issued, when NEW or
CLEAR are used or when the program is editted. Effectively they
are only available when a Basic program is running. Examples:
INSTALL "catlib"
LIBRARY "doglib"
Libraries loaded using 'INSTALL' cannot be discarded. However the
same library can be loaded via 'LIBRARY' and it will effectively
take precedence as libraries loaded this way are searched first.
Libraries can be held as plain text, with or without line numbers,
or can be tokenised.
Local Variables in Libraries
----------------------------
It is possible for libraries to have variables and arrays that are
private to that library. This is an extension to Basic V. These
are covered in more detail below.
Differences Between Brandy and Acorn's Interpreter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Brandy is compatible with the Acorn interpreter and should produce
the same results as the Acorn one. However perfect compatibility
cannot be achieved for a number of reasons, for example, the lack
of graphic commands in some versions of the program greatly limits
which programs will work. There are also some enhancements that
could lead to incompatibilites, for example, Brandy allows strings
to be up to 65536 characters long compared to the Acorn
interpreter's limit of 255. The list of differences are as
follows:
1) Only the RISC OS version has graphics and sound. The DOS
implemention supports a subset of the graphics commands.
2) Brandy has no support for machine code programs. It does not
support either the 'CALL' statement nor the 'USR' function
(except for one specific case, to use OS_Byte call 0 to
identify the host type). The built-in assembler has not been
implemented.
3) Only the RISC OS version supports the 'SYS' statement.
4) The follow Basic commands have not been implemented: APPEND
and AUTO.
5) The 'OVERLAY' statement has not been implemented.
6) The functions 'INKEY' and 'INKEY$' have only been implemented
fully for RISC OS as yet.
7) Not all of the VDU commands have been implemented yet in
non-RISC OS versions.
8) Cursor editing is not available in non-RISC OS versions.
9) 'WIDTH' has not been implemented. 'PRINT' leaves something
to be desired too.
10) The TRACE option 'TRACE STEP' has not been implemented yet.
11) Some 'LISTO' options have not been implemented yet.
12) The 'END=' version of the END statement is not supported.
13) Brandy behaves differently to the Acorn interpreter after
an error when the program contains ON ERROR or ON ERROR
LOCAL statements to trap errors.
The major omissions in the versions of the interpreter that run
under operating systems other than RISC OS are graphics and sound.
The built-in assembler and support for machine code programs are
missing too. Apart from that, the interpreter is essentially a
full implementation of the Acorn interpreter.
The interpreter has the following extensions:
1) Strings can be up to 65536 characters long.
2) Statements can be up to 1024 characters long.
3) Libraries can have their own private variables.
4) The OSCLI statement has been extended to allow the output from
operating system commands to captured.
5) The case of commands such as 'LIST' and 'RUN' is ignored, so
'LIST' could be entered as 'list' or 'List'. The downside is
that variable names that are the lower case equivalents of
commands will now be seen as commands, something that seems
to happen all too frequently.
6) There is a new pseudo-variable 'FILEPATH$' that gives a
list of directories to be searched when loading programs and
libraries (see the section on this below).
7) There are two functions for dealing with command line
parameters, 'ARGC' and 'ARGV$' (see the section below).
8) There are two new string functions, 'VERIFY' and 'XLATE$'
(see the section below).
9) 'NEW' can be followed by a parameter, the new size of the
Basic workspace. This allows it to be changed from the
default of half a megabyte (see section on this below).
10) The 'RUN' command can be followed by the name of a program
to run. It behaves just like the statement 'CHAIN'.
11) The 'RUN' command can also be followed by a line number to
start program execution at that line.
12) There is an extra 'TRACE' option: 'TRACE GOTO'. This prints
out the source and destination line numbers of any branches in
the program.
13) 'TRACE PROC' shows returns from procedures and functions as
well as when they are called.
14) Individual TRACE options may be turned off and on, for example,
'TRACE PROC OFF' will turn off the only the procedure trace
and leave any other running.
15) There is an extra 'LISTO' option, 32. When this option is in
effect, listing of a program pauses every twenty lines with
the prompt '-- more --'. Press the space bar to show the next
twenty lines, 'return' to print just the next line or the
'Escape' key to stop the command.
16) 'LISTO' can be used as a function to find out the current
setting of 'listo'.
17) There are a couple of extra 'LIST' commands. 'LISTB' dumps
memory in byte form between the two addresses specified.
'LISTW' is the same, but dumps memory as words. These were
added for debugging but will probably be left in.
18) The 'EDIT' command on its own invokes a text editor to edit
the program. Under RISC OS it calls StrongEd Zap, Edit or
'twin', under Linux and NetBSD it calls 'vi' and under DOS
it calls 'edit'.
19) 'EDIT' followed by a line number allows that line to be
edited using the built-in line editor. This feature is not
available under RISC OS.
20) When a program is loaded via a 'LOAD' command the name of the
file is kept and saving the program using the 'SAVE' command
with no argument will save the program using that name.
21) Programs are always saved as plain text.
22) The latest extended versions of COLOUR, GCOL, MODE and
DIM are supported. VDU can also be used as a function to
read RISC OS mode variables. COLOUR can also be used as
a function to return a number that represents the closest
match to the colour whose colour components were passed
to the function.
There is quite a list here but really apart from the longer
maximum string and statement lengths, local variables in
libraries and the change to 'new', most of these are really
cosmetic changes.
Local Variables in Libraries
----------------------------
Libraries can have their own private variables and arrays. The
variables are only accessible in the library in which they were
declared.
The LIBRARY LOCAL statement is used to declare the variables. The
syntax is as follows:
LIBRARY LOCAL <list of variables and arrays>
where <list of variable and arrays> is a list of variable and
array names separated by commas, for example:
LIBRARY LOCAL abc%, def%, ghi$, jkl(), mno(), pqr$()
In the case of arrays, this merely defines that the array is local
to the library. The dimensions of the array have to be declared
using a DIM statement in the normal way, for example:
LIBRARY LOCAL jkl(), pqr$()
DIM jkl(100), pqr$(table_size%)
There can be as many LIBRARY LOCAL and DIM statements as
necessary but they have to be before the first DEF PROC or DEF FN
statement in the library. They also have to be the first item on
the line.
The variables can only be referenced in the library. They are not
visible outside it. This is different to the way in which local
variables are dealt with in a procedure or function, where local
varables can be accessed by any procedure of function called by
the procedure in which they were declared. They can duplicate the
names of variables in the Basic program or other libraries.
When looking for a variable in a library, the interpreter first
searches for it amongst the library's private variables and then
in the Basic program's.
The variables and arrays are created the first time the library is
referenced. In practice this means that they are set up when
the interpreter has to search the library for a procedure or
function.
Private variables in a library can further be used as local
variables in a procedure or function. Note that they can only be
accessed in the library, for example:
LIBRARY LOCAL abc%, def, ghi$, jkl(), mno$()
DIM jkl(100)
DEF PROCaaa(abc%)
LOCAL def, ghi$
ENDPROC
DEF PROCbbb(def, jkl())
LOCAL mno$()
DIM mno$(100)
ENDPROC
DEF PROCccc(xyz, abc%)
ENDPROC
Here, abc%, def, ghi$, jkl() and mno$() are all declared to be
private to the library. The dimensions of jkl() are also defined.
In PROCaaa, abc% is used as a formal parameter (effectively a
local variable) and def and ghi$ declared to be local to the
procedure. Any procedure or function *in the library* that PROCaaa
calls that use def and ghi$ will use PROCaaa's local versions.
Any procedure or function that PROCaaa calls that are *outside*
the library *will not* see these variables.
In PROCbbb, def and jkl() are used as formal parameters and mno$()
is defined as a local array and its dimensions given. Note that
this is the first place where the dimensions have been defined.
In PROCccc, two variables are used as formal parameters, xyz and
abc%. This case is more complex in that abc% is one of the
library's private variables whereas xyz is not. xyz is one of the
Basic program's variables. abc% can only be referenced in the
library but xyz is visible anywhere.
The rules for the scope of private library variables may sound
complex but they are quite simple. The point to remember is that
a private variable in *only* accessible in the library in which it
was declared. If a variable is not declared on a LIBRARY LOCAL
statement then it is visible anywhere.
FILEPATH$
---------
This is an extra pseudo variable. It gives a list of directory
names that the interpreter will search when looking for programs
and libraries. The names are separated by commas with no
intervening blanks or other white space characters, for example:
FILEPATH$="/home/dave,/usr/local/basic/lib"
The format of the directory names is operating system-dependent
and the program assumes that they are correct.
FILEPATH$ can be treated like any other string variable except
that only the '=' assignment operator is allowed, thus:
FILEPATH$="/usr/local/basic/lib"
is fine but:
FILEPATH$+=",/usr/local/lib"
is not supported and will give an error.
The interpreter first of all tries to find the program or library
using the name as supplied. If it cannot find it and the name is
just the name of a file, that is, it does not contain any
directories, it then looks in each of the directories given by
FILEPATH$ until either it finds the file or it reaches the end of
the list. If the file can be found, the name of the file as far as
the interpreter is concerned is the name as orginally supplied
with the name of the directory in which it was found prepended to
it, for example:
load "earthworks"
If this program was found in the directory '/home/dave' the name
of the program would show up as '/home/dave/earthworks' in the
output from 'help'. Saving the program without specifying a new
file name would write to the file '/home/dave/earthworks'.
As FILEPATH$ is a pseudo variable, its value is not affected by
CLEAR or NEW. The initial value of FILEPATH$ can be set using the
command line option '-path'.
The main purpose of FILEPATH$ is to provide a search path for
libraries but it is also used when looking for programs. It
would be useful here for 'CHAIN'.
Use of FILEPATH$ can effectively be disabled by setting it to
the empty string, that is, by entering 'FILEPATH$=""'.
ARGC and ARGV$
--------------
These functions return parameters from the command line used to
start the interpreter. ARGC returns the number of parameters and
ARGV$ the parameters themselves.
ARGC
----
Returns the number of parameters, for example:
count = ARGC
ARGV$
-----
Returns parameters. The syntax is:
ARGV$ <factor>
where <factor> is a numeric value that identifies the parameter
to return, for example:
FOR N%=1 TO ARGC
PRINT ARGV$ N%
NEXT
Parameter numbers are in the range 1 to the value returned by
ARGC. ARGV$0 is the name of the Basic program if it was started
from the command line otherwise it is an empty string.
XLATE$
------
This function is used to translate character strings. There are
two forms of it as follows:
XLATE$(<string>)
XLATE$(<string>, <translate table>)
In the first version, the function returns the string <string>
converted to lower case. Note that only ASCII characters are
converted. The second version is more powerful in that <string>
is converted according to the user-supplied translate table
<translate table>. This can be either a character string or a
one dimensional string array. The effect is the same in both
cases: each character in the original string is replaced by
the corresponding character in the translate table. If the
table is a string, the character at offset 1 replaces the
character with ASCII code 0, the character at offset 2
replaces the one with ASCII code 1 and so forth. It is not
necessary for the string to be 256 characters long: any
character whose code would place it beyond the end of the
string is left unchanged. The use of a string array is more
convenient in that each character is replaced by the array
entry corresponding to its ASCII code. Note that only the
first character of the string in the array is used. If the
array entry contains an empty string then the original
character is left unchanged. As with the character string
translate table, the array does not have to contain 256
elements: characters whose ASCII code place them beyond the
end of the array are left unchanged.
Examples:
PRINT XLATE$("AbCdEfGh")
DIM table$(255)
FOR N%=ASC"0" TO ASC"9": table$(N%)="*": NEXT
PRINT XLATE$("abc123def456", table$())
VERIFY
------
The format of this function is as follows:
VERIFY(<string 1>, <string 2> [, <start>])
It returns the offset (from one) of the first character in
string <string 1> that is not in string <string 2>. <start>
is an optional parameter that gives the offset at which to
start the check. If all the characters in <string 1> are
present in <string 2> the function returns zero; otherwise
it returns the offset of the first bad character.
Examples:
X% = VERIFY(a$, "0123456789")
REPEAT A$=GET$: UNTIL VERIFY(a$, "YNyn")=0
P%=1
REPEAT
P%=VERIFY("...x..x..", ".", P%)
IF P%<>0 THEN PRINT P%
UNTIL P%=0
If <string 1> is an empty string or the start position is
greater than the string length then the function always
returns zero. If <string 2> is an empty string then the
unction always returns one or the value of <start> (if
this is supplied).
BBC Basic 1.26 Extensions
-------------------------
The following statement types have been extended in this
version of the interpreter:
COLOUR
DIM
GCOL
MODE
VDU function
COLOUR
The new 'OF' and 'ON' parts are supported, for example:
COLOUR OF 255,255,255 ON 0,0,0
DIM
It is now possible for local byte arrays to be created in
procedures and functions. The memory for the byte array is
reclaimed when the procedure or function ends, for example:
DIM pointer% LOCAL 1000
GCOL
The new 'OF' and 'ON' parts are supported, for example:
GCOL OF 0,0,0 ON 255,255,255
MODE
The extended form of MODE where the screen size to be used
is supplied is now supported. Example:
MODE 800,600,8
VDU Function
VDU can now be used as a function to return the values of mode
variables. Example:
PRINT "Width in characters is ";VDU 1
All of these extensions are described in the file 'basic'.
COLOUR function
This returns a value that represents the colour with the
closest match in the current screen mode to the colour with
the colour components passed to the function. The value is
for use with the COLOUR OF and GCOL OF statements. Example:
red = COLOUR(255, 0, 0)
blue = COLOUR(0, 0, 255)
COLOUR OF red ON blue
This could also be written as:
COLOUR OF 255, 0, 0 ON 0, 0, 255
or even:
COLOUR OF COLOUR(255, 0, 0) ON COLOUR(0, 0, 255)
The advantage of the new forms of GCOL and COLOUR are that
they are mode independent. They are more flexible than the
old versions of the statements and do away with the need for
TINT.
Command Line Parameters
-----------------------
The interpreter assumes that any unrecognised parameter on the
command line is meant to be for the Basic program, for example:
brandy aprog parm1 parm2 -xyz
would be assumed to consist of the name of the program to run,
aprog, and three parameters for the program, 'parm1', 'parm2' and
'-xyz'.
brandy aprog -size 256k parm1 parm2 -xyz
would be interpreted in exactly the same way. '-size 256k' would
be treated as an option for the interpreter itself.
Beware of cases like:
brandy aprog -size 256k parm1 -start
Here, '-start' would be seen as '-size' by the program as it
only checks for '-s' to identify '-size'.
Capturing Command Output with OSCLI
-----------------------------------
The OSCLI statement has been extended so that the output from
operating system commands can be read by the program. The syntax of
the statement is now:
OSCLI <command> [ TO <string array> [ , <variable> ] ]
<command> is a string expression that is the command to be issued.
<string array> is an array that will be used to hold the output
from the command. It is optional. If it is not present then the
command output goes to the normal place. <variable> is set to the
number of lines stored in <string array>. Again, it is optional.
The existing contents of <string array> are discarded before the
output from the command is stored in it. Elements of the array
that are not used are set to the empty string. The first element
of the array used is 1, so the output is found in elements 1 to
<variable>. If there is more output than will fit in the array the
excess is discarded. There is nothing to indicate that this has
happened so it is up to the user to ensure that the array is large
enough.
Example:
OSCLI "ex" TO array$(), lines%
FOR N%=1 TO lines%
IF LEFT$(array$(N%), 1)="a" THEN PRINT array$(N%)
NEXT
Note that there some problems still to be resolved with OSCLI ...
TO. Errors (or to be more precise, messages written to stderr) are
not caught in the DOS version of the program as DOS does not
provide a way to redirect them. They are therefore missed out.
The NEW Command
---------------
The NEW command has been extended to allow the size of the Basic
workspace to be changed. By default, Brandy allocates half a
megabyte of memory to hold the program, variables, strings and so
forth. This can be changed by means of the 'NEW' command as
follows:
NEW <size>
where <size> is the new size of the workspace in bytes, for
example:
NEW 1000000
would set the workspace size to 1,000,000 bytes.
Note that using this command will result in the loss of the
current contents of the workspace, including any programs and
libraries (except for libraries loaded by means of the 'INSTALL'
command). It is not possible to recover a program by means of
'OLD' under these circumstances.
The minimum size allowed is 10K bytes. The upper limit is whatever
the operating system on which the interpreter is running allows.
Note that the initial size of the Basic workspace can also be
set using the command line option '-size'.
SAVE
----
There are two versions of the 'SAVE' command used to save a
program. 'SAVE' uses the current 'LISTO' setting to control the
format of the program when it is written to disk. 'SAVEO' allows
the format to be more precisely specified. The format of the SAVEO
command is:
SAVEO <format> [,<filename>]
where <format> is a number that gives the 'listo' format to be
used and <filename> is the name of the file. The name can be
omitted, in which case the name defaults to either the name used
on the last 'LOAD' command or the name given on the first line of
the program. Example:
SAVEO 10,"test"
would save a program called "test" using 'listo' option 10 (omit
line numbers and indent lines inside loops, block IF statements
and so forth).
OLD
---
The OLD command is supported but is only of limited use in this
interpreter. It only works when trying to recover a program
immediately after typing 'NEW'. It does not work after
'NEW <memory size>' variant of NEW, nor can it be used after
quitting from the interpreter and rerunning it.
The Acorn Basic trick of having many programs in memory at once
and switching between them by modifying PAGE and typing OLD does
not work. 'OLD' works in a different way to the version in
Acorn's interpreter.
TRACE
-----
Several changes have been made to the TRACE command.
TRACE PROC
----------
This shows both when a procedure or function is entered and when
it is exited. '==>PROCabcd' indicates that PROCabcd has been entered
and 'PROCabcd-->' shows that it has been exited.
TRACE GOTO
----------
The purpose of this option is to trace program flow. It logs all
jumps in the code, showing the number of the line at which the
branch occured and the line at which execution continues. It
works not just for GOTO statements but anywhere where a branch
can occur, for example, in IF statements. Example: consider the
following code:
100 IF X%<10 THEN
110 PRINT"X% is less than ten"
120 flag%=TRUE
130 ELSE
140 PRINT"X% is greater than or equal to ten"
150 flag%=FALSE
160 ENDIF
170 PRINT flag%
If X% was set to five, the branch trace would show the following
entries:
[100->110][130->170]
and if X% was set to 25, it would look like:
[100->140]
(Note that the program output has been omitted for clarity here).
In the first case, as X% is less that ten the condition is true
and so the program branches to line 110. When it reaches the ELSE
it branches from the ELSE to the line after the ENDIF. In the
second case, as the condition is false the program flow passes
from line 100 to the line after the ELSE. As there is no branch
at the end of the ELSE part of the 'IF' and control runs straight
through to line 170, there is no trace entry.
FOR, WHILE and REPEAT loops, procedure and functions calls and
returns, GOTO, GOSUB, ON GOTO, ON GOSUB, ON PROC and RETURN
statements are all traced by this option. Note, however, that
some of the trace entries are not intuitive, for example, the
line number of the start of a WHILE loop will be that of
the statement after the WHILE itself, for example:
200 X%=7
210 WHILE X%<10
220 X%+=1
230 ENDWHILE
will produce the following trace:
[230->220][230->220]
The reason for this is tied up in the way WHILE loops work.
It is considered that this trace cuts out much of the 'noise' that
results from simply tracing line numbers.
TRACE <option> [ON | OFF]
-------------------------
Individual trace options can be turned on and off without
affecting any other settings, for example, 'TRACE PROC OFF' turns
off the procedure and function call trace. 'TRACE OFF' turns off
all traces. 'TRACE <option> ON' is provided for consistency.
'TRACE PROC' and 'TRACE PROC ON' both turn on the procedure and
function call trace.
TRACE <line number>
-------------------
This is not supported.
TRACE STEP and TRACE PROC STEP
------------------------------
These have not been implemented yet.
ON ERROR and ON ERROR LOCAL
---------------------------
ON ERROR and ON ERROR LOCAL provide a means for errors to be
trapped in a Basic program. The documentation for these in the
Acorn interpreter says that the effect is as if there is a GOTO
statement that takes you from the point of the error to the
statements after the ON ERROR clause. There is little (if any)
cleaning up after the error. Brandy differs from the Acorn
interpreter in that it tidies up before restarting at the ON ERROR
statement: LOCAL variables and arrays are reset to the state they
were in at the point of the ON ERROR and procedures and functions
ended cleanly. The intention is to provide something closer to
exception handling than what the Acorn interpreter has.
EDIT
----
The EDIT command loads the Basic program into a text editor. The
program is reloaded by the interpreter when leaving the editor.
The editor used by default varies from operating system to
operating system as follows:
RISC OS StrongED, Zap, Edit or Twin.
Linux vi
NetBSD vi
DOS edit
Beos vi
It is possible to override which editor the program uses by means
of an environment variable. Under Linux and NetBSD it looks for
the standard 'EDITOR' environment variable. Under RISC OS it looks
for 'Brandy$Editor'. The DOS version checks for 'EDITOR'. Care
should be taken with DOS to choose an editor that runs under DOS
and not Windows due to the way in which DOS/Windows invokes the
editor. (The editor is started as a separate program from the
interpreter and the interpreter itself continues to run rather
than being suspended until the editor has finished.)
Under RISC OS, if the interpreter is being run in the desktop,
the Basic program is transfered to the editor, for example,
StrongED, and the interpreter halted. When the file being edited
is saved brandy wakes up and reloads the program. The interpreter
can also be restarted by pressing the 'Esc' key, but it will not
reload the Basic program if this is done. If the program is
running outside the desktop it will invoke Twin but this does
not work very well as the interpreter does not support the way
in which Twin operates.
Unless the Basic program contains statements such as GOTO that
reference line numbers, they can be completely ignored in a text
editor. Lines can be added without line numbers or moved around
without any problem. The lines of the Basic program will be
renumbered when the program is reloaded by the interpreter.
NOTE: There are two mistakes that are very, very easy to make
with the RISC OS editor support. Firstly, once the file has been
edited and saved, the file as displayed in StrongED or Zap is
redundant. The editing session has finished and any further
editing of that file will not affect the version of the program
that the interpreter is working with. It is easy to forget this
and to continue making changes to the program in the editor. The
second mistake is to forget to save the edited program from within
Brandy. When the file is saved in the editor it is being returned
to Brandy, not being saved on disk. Again, it is very easy to
forget this.
EDITO
-----
There is a variation on the EDIT command, EDITO, that affects how
the program is formatted when it is passed to the editor. The
command syntax is:
EDITO <value>
where <value> controls how the program will be formatted. This
takes the same values as 'LISTO' and it has the same effect.
EDITO allows, for example, a program to be passed to the editor
without line numbers. 'EDITO 8' is the command to use here. If
EDIT is used, the program is formatted according to the current
'LISTO' setting. EDITO otherwise works in the same way as EDIT.
Line Editor
-----------
The Linux, NetBSD and DOS versions of the interpreter have a
simple built-in line editor. Apart from allowing input lines to be
edited, there is also a command line history feature that allows
the last twenty or so lines entered to be recalled. The editing
commands are:
Cursor left or Ctrl-B Move one character left
Cursor right or Ctrl-F Move one character right
Home or Ctrl-A Go to start of line
End or Ctrl-E Go to end of line
Delete or Ctrl-D Delete character under cursor
Backspace or Ctrl-H Delete character to left of cursor
Ctrl-K Delete from cursor to end of line
Ctrl-U Delete whole line
Insert Toggle between 'insert' and 'overwrite' mode
Cursor up or CTRL-P Go back one entry in the command line history
Cursor down or CTRL-N Go forwards one entry in the command line history
The aim is to provide both DOS and Unix (emacs) style editing.
The 'Escape' Key
----------------
Under operating systems other than RISC OS and DOS the 'escape'
key is not the 'Esc' key but Control-C, that is, to break into a
program press the keys 'Ctrl' and 'C' at the same time.
Identifying the Environment Under Which Brandy is Running
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There are three things a program can check to figure out what
operating system is it running under:
1) Check the contents of !PAGE. If this is set to &D7C1C7C5
then the Basic program is running under Brandy. This value
is a constant. Other Basic V interpreters store a different
value there, for example, ?PAGE on the Acorn interpreter
returns &0D.
2) Check what INKEY -256 returns. This has been the documented
way of checking the OS version since the first version of
RISC OS. The values returned are:
&A0 Arthur 1.2
&A1 RISC OS 2.00
&A2 RISC OS 2.01
&A3 RISC OS 3.00
&A4 RISC OS 3.10 and 3.11
&A5 RISC OS 3.50
&A6 RISC OS 3.60
&A7 RISC OS 3.70 and 3.71
&A8 RISC OS 4.00, 4.01, 4.02 and 4.03
&A9 RISC OS 4.32 to 4.37
&AA RISC OS 5
Brandy adds the following:
&F5 Amiga
&F6 OpenBSD
&F7 FreeBSD
&F8 MACOS X
&F9 Linux
&FA DOS with DJGPP DOS extender
&FB Beos
&FC Windows 32
&FE NetBSD
Other values might be added to this list for other operating
systems.
3) The hardware type and general environment type can be found by
checking what is returned by OS_Byte 0. The USR function is not
supported except in one special case, to make the BBC Micro
MOS OSBYTE call. The following code can be used:
A% = 0: X% = 1: result% = USR &FFF4
version% = (result% DIV 256) AND 255
version% will contain one of the following values:
6 Acorn hardware (RiscPC, A7000 and so forth)
8 Unix-type OS
32 PC (DOS and Windows)
Again, this list might be extended.
I/O Redirection
~~~~~~~~~~~~~~~
Under RISC OS, NetBSD and Linux it is possible to use the
operating system's I/O redirection facilities to take input from
and write output to a file rather than use the keyboard and screen
respectively. Under NetBSD, for example, commands could be taken
from a file thus:
brandy <command.list
Or read from one file with output going to a second file using:
brandy <command.list >output.file
Under RISC OS these would be:
brandy { < command.list }
and
brandy { < command.list > output.file }
Under NetBSD and Linux, redirecting output to a file disables all
of the VDU commands except for VDU 7, 8, 9, 10, 13 and 27. The
interpreter flags an error if any VDU command apart from the ones
listed is used unless the command line flag '-ignore' is used,
in which case it is just ignored. The reason for this is to make
the program only write plain text to the file. Similarly,
redirecting input disables the functions GET and INKEY as well as
the command line editing and recall features.
RISC OS behaves differently in that nothing is disabled by using
I/O redirection.
The DOS version of the program does not yet fully support I/O
redirection. Input can be redirected in the same way as the NetBSD
and Linux versions but output redirection still needs some work
done on it in the current version of the interpreter, 1.13.
(Aside: It works if the program is compiled with textonly.c but
not if textgraph.c is used. Textgraph.c supports graphics but
textonly.c does not, so the choice is between a version of the
program that has graphics and no output redirection or no graphics
and does support output redirection.)
The current Windows version of the program does not support I/O
redirection at all.
When input redirection is used, each line from the file is read
and executed at Brandy's command line. These can be commands to
load and run programs or Basic statements. Within the limitations
of what can be run as a single statement from the command line,
entire Basic programs can be run this way.
One useful command is 'QUIT', which can be used to finish the run
of the interpreter. The run is also stopped if the end of the file
is reached.
An example might help here. Consider the following:
LOAD"examples/sieve"
RUN
LOAD"examples/hex"
RUN
IF X%=10 THEN QUIT
RUN
QUIT 100
If this is saved in a file (for example, command.bbc), then
typing:
brandy <command.bbc
would run the interpreter. It would read each line of the file and
execute it. Note how the IF statement is used to end the run of
the interpreter before the end of the file is reached because some
condition is true. It should not be forgotten that after running
a program, all of its variables are still available until it is
run again or another program is loaded. At the end QUIT is used to
halt the run of the interpreter and return a status code of 100 to
the operating system. (The interpreter normally returns a status
code of 0.)
Using Basic as a Script Language Under NetBSD and Linux
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Basic is not really designed for use as a script language but it
can be used in this way under NetBSD and Linux. If the first line
of a Basic program contains the name of the interpreter and the
file containing the Basic program is made executable, the
interpreter will automatically be used to run the program, for
example, conside the following program:
#!/usr/local/bin/brandy
PROCprint
QUIT
:
DEF PROCprint
PRINT "Hello"
ENDPROC
If this is saved in a file (called, for example, 'hello.bbc')
and the file is made executable with the command:
chmod +x hello.bbc
then typing:
hello.bbc
will invoke brandy and pass the name of the program (hello.bbc)
to it. Brandy ignores the first line as it starts with '#!' but
reads the rest of the program and runs it. Note the use of the
QUIT command to exit from the interpreter once the Basic program
has finished.
One important point to note here is that the example assumes that
there is a copy of Brandy in the directory /usr/local/bin.
Using Brandy in this way is different to I/O redirection. Here,
the interpreter is being invoked with a program. Using input
redirection, Brandy is passed a string of commands that it
executes at the command line.
The SYS Statement
~~~~~~~~~~~~~~~~~
The SYS statement is used to make calls to the operating system
on machines that run RISC OS. It is envisaged that the same
mechanism will be used under other operating systems.
The 'key' Command
~~~~~~~~~~~~~~~~~
A new feature in Brandy 1.16 is that it emulates the RISC OS
'key' command to allow strings to be assigned to function keys.
This is an operating system command under RISC OS that is
emulated by the interpreter. The command is issued using OSCLI
in the normal way. The format is:
key <key number> <string>
where <key> is the function key number in the range 0 to 15
and <string> is the string assigned to that key. Pressing
that function key will insert the string into the keyboard
buffer, for example:
OSCLI "key 3 run"
will assign the string "run" to function key 3.
There is a simple escape mechanism to allow control characters
to be included in the string. This is of the form:
|<letter>
where <letter> is a letter.
The escape sequence '|m' is used to represent a 'newline'
character, so:
OSCLI "key 3 run|m"
will set up function key 3 to insert "run" and a newline
character into the keyboard buffer, so that pressing F3 will
issue the command.
The string can be enclosed in double quote if desired, for
example:
OSCLI "key 4 " ": REM Insert five blanks
There is a command line option that can be used to tell the
program to pass all commands to the underlying operating system
rather than check them to see if they are RISC OS commands
emulated by the interpreter. This is '-nostar'.
Note: The key command has not been fully implemented in that
the RISC OS version allows a greater range of escape sequences.
Also, it does not check for silly commands.
Other emulated RISC OS commands could be added if desired.
Performance
~~~~~~~~~~~
The Acorn Basic interpreter is written in ARM assembler. Brandy is
in C and there is therefore no chance that it will come remotely
close to the Acorn interpreter in terms of speed. The RISC OS
version, for example, runs between two and five times slower
when working with integers and is up to twelve times slower when
floating point numbers are used extensively. That said, the
performance is quite respectable on a faster processor.
Important Error Messages
~~~~~~~~~~~~~~~~~~~~~~~~
Attention should be drawn to three of the error messages that the
interpreter can produce:
The interpreter has gone wrong at line <x> in <y>
This indicates that the interpreter has lost the plot. It says
that there is possibly something wrong with the Basic program in
memory but the more likely cause is that the interpreter has run
across a token that either has an illegal value or that should not
be encountered in the context in which it was found. In short
there is almost certainly a logic error in the interpreter. <x>
and <y> give the line number and name of the module of the source
code of the interpreter at which the problem was detected.
Unsupported Basic V feature found
Unsupported Basic V statement type found
The statement contains something that is not supported by this
version of the interpreter. The most likely culprit is a graphics
or sound statement. (It might be possible to make the program
run by using the command line option '-ignore'. This tells the
intepreter to ignore 'cosmetic' unsupported features, such as
changing the screen colours.)
These are regarded as fatal errors and cannot be trapped by
means of 'ON ERROR'.
Known Problems
~~~~~~~~~~~~~~
There are no major known bugs in the program but there are a
few minor issues as follows:
1) 'PRINT' could be better implemented. 'WIDTH' is not
handled correctly and the way in which floating point
numbers are output could be better.
2) Assigning too large a floating point number to an integer
variable does not produce an error. On X86, 'A%=123E45'
sets A% to 0x80000000. It does not say that the value is
out of range. NetBSD does much the same thing, setting the
variable to either 0x7fffffff or 0x80000000 depending on
the sign of the floating point number. Under RISC OS an
exception is raised (SIGFPE), which is what is wanted.
3) If an error occurs when renumbering the lines of a program
when the program is being loaded, the line number of the
line in error is not listed. The reason is that 'top' has
not been updated at this point and so searching for the
line fails. (Effectively there is no program in memory yet
as far as the interpreter is concerned.)
4) COLOUR <red>,<green>,<blue> is not fully implemented.
5) GCOL <red>,<green>,<blue> has not been implemented at all.
6) Under Linux and NetBSD, pressing Ctrl-C when a program is
waiting for input should abort the Basic program immediately
but at the moment another character has to be typed after
pressing Ctrl-C.
Miscellaneous Comments
~~~~~~~~~~~~~~~~~~~~~~
Some miscellaneous comments:
TIME When running under NetBSD and Linux, the function TIME
returns the processor time used by the program, not the
elapsed time. It always starts from zero and is therefore
useless as a way of seeding the random number generator,
that is, RND(-TIME) will not give the desired result.
TIME= This is supported.
TIME$= This is ignored.
MID$()= There is a difference between Brandy's and Acorn Basic's
implementation of 'MID$()='. In Acorn's interpreter, if
the starting position exceeds the maximum length of a
string (255 characters) the start of string is overwritten.
In Brandy, nothing is changed in the original string if the
starting position of the new string exceeds the length of
original string.
RIGHT$ Brandy does not precisely emulate the Basic RIGHT$ function.
For small negative values of the string length Acorn Basic
returns a null string but for large negative values it
returns the original string. 'RIGHT$(A$,-33024)' returns
a null string but 'RIGHT$(A$,-33025)' returns the value
of A$. Brandy always returns a null string if the length
is negative.
Block IF Statements
There is what looks like a bug in Brandy at first glance
involving block IF statements. The following program
behaves differently under the Acorn interpreter and Brandy:
X%=10
IF X%=1 THENREM X is 1
PRINT"X is 1"
ELSE
PRINT"Hello X is ";X%
ENDIF
The Acorn interpreter prints 'X is 1' but Brandy prints
'Hello X is 10'. The reason for this is that Brandy always
sees the IF statement as a block IF. The REM statement is
ignored as programs are always run in a 'crunched' form
therefore as there is nothing after the 'THEN' the
statement is identified as a block IF. In the case of the
Acorn interpreter, the 'THEN' is not at the end of the
line and it is taken as a single line IF.
If the program is crunched in the Acorn interpreter by
typing 'CRUNCH 31' its behaviour changes. It now prints
'Hello X is 10', that is, the IF statement is now seen
as a block IF as the REM statement has been discarded.
The moral of the story is that Brandy runs programs in
a crunched form.
Floating Point Number Formats
There is an incompatibility between the versions of the
program that run on ARM processors and those that run on,
for example, a X86, that affects floating point numbers.
A file containing floating point numbers written on an
ARM processor using PRINT# cannot be read on a processor
with a X86 via INPUT# as the format in which the numbers
are written to the file is different. On a ARM processor,
eight byte floating point numbers are held in the order
'aa bb cc dd ee ff gg hh' but on a X86 they are in the
order 'ee ff gg hh aa bb cc dd'. Whilst this is a minor
issue, it might cause problems. It will be resolved in a
later version of the program.
Keyboard Mapping Under DOS and Windows
DOS and Windows have separate keyboard mappings. If
Brandy is compiled as a DOS program (as it is when using
DJGPP) the program uses the DOS keyboard mapping when
reading anything from the keyboard. If this has not been
changed from the default (by means of statements in
AUTOEXEC.BAT and CONFIG.SYS) and the program is run in a
DOS box under Windows, it could appear as if the keyboard
mapping is wrong. The answer is to add the relevant
statements to the files named above.
The WAIT statatemt
Under DOS, the 'WAIT <time>' statement does not always
halt the program for the time given by <time>. On some
types of PC it seems to wait for up to 25% longer than
it should, yet on others it works as expected. This
problem does not affect other operating systems.
Conclusion
~~~~~~~~~~
It has been said that Basic is a poor language and that nobody
seriously uses it. In my opinion Acorn's dialect, Basic V, is an
excellent one and worth looking at. It has its faults and lacks
any support for current practices such as object oriented
programming. On the other hand the language is simple and the
interpreter requires no special packages or additional libraries
on the machine on which it runs. Basic V is easy to use and
substantial programs can be written using it. It is good for
small, one-off programs or for experimenting. It can also make
programming enjoyable again.
This is the first version of the program. It seems to be quite
stable but plenty of bugs still lurk. They are many rough edges
and a number of minor features have only been partially
implemented as yet. There is plenty of scope for improvement.
Contact
~~~~~~~
If anybody has any suggestions or improvements for the program
or finds any bugs, I can be email'ed at:
dave_daniels@argonet.co.uk
Alternatively post a message on the comp.sys.acorn.programmer
newsgroup.
