Updates on my TRC interpreter on the JVM

vintzend

Quite some time ago I started investigating the binary TRC format (the tokenized code that the True BASIC compiler compiles BASIC source code to) format.

Not so long ago I decided to write my own interpreter around it, in Java and see how far I could get it to go.

It's a bit too early to share anything, really, but perhaps it helps my motivation to work on it by giving occasional updates. It's a spare time project and in the very early stages. Don't hold your breath that it will ever be able run full True BASIC programs.

But it can already run some simple BASIC commands. Recently I finished support for all datatypes. I've had a lot of fun working on this interpreter.

Here you can see a screenshot: https://twitter.com/vintzend/status/1447182111581085697/photo/1

At upper-left you see the True BASIC Silver 5.5 editor with the code that I'll be running. In the middle you see me compiling it with TBSYSTEM.EXE from TB (which I have in my Windows path)., which produces the TRC file that my interpreter should be able to run. At the right you see the hex editor that I use to inspect the binary TRC code produced by the TB compiler.

Finally I ran the TRC file in my interpreter and at the bottom you see the output produced while it was running (it was running directly inside Eclipse IDE, the IDE I use for my own Java projects).

Why?

A valid question would be: why am I writing an interpreter for TRC files and not TRU (True BASIC source code) files?

Well, at this time I'm not interested in writing my own full text parser and compiler (although that will be the best way to bring True BASIC to this century, I have no doubts about that). But there's only so much spare time that I can spend on this project. Also, I thought it would be the most fair to the current owners of True BASIC: one would still need to buy a compiler (and all libraries) from True BASIC, before my project will be of any value.

Also, I see it as an experiment. I'm not promising I'll be ever able to deliver a full mature runtime.

Disclaimer

Note that I am not associated with the current owners of True BASIC. Don't blame the fine people at True BASIC for my mistakes, my (lack of) work , etc. ;-). I don't intend to make any money of this project. And again: I see it as an experiment. I call it "TRC Interpreter for JVM", so I'll try not to infringe on any branding/trademarks.

To try to keep my motivation, I'll update the post after this one regularly when I have added and/or discovered new stuff and will post general updates from time to time in this topic.

vintzend

Vincent's TRC interpreter (for Java Virtual Machine)

Last updated: November 18, 2021

(Possibly not all complete TB behavior is ported yet. Where I'm aware of limitations, omissions, etc. I tried to note it down below)

Supported data types

Numeric
- Internally stored as either 8-byte double precision numbers, or 32-bit integer
- TODO: Implement scientific notation
- TODO: Check overflows
Strings
- TODO: Implement max length
- TODO: I expect various bugs with the handling of escaped double-quotes (PRINT """HELLO""")
Numeric arrays (single and multi-dimensional)
String arrays (single and multidimensional)

Supported program units

Main program
Internal subroutines (sub-routines before END)
Internal functions (functions before END)
External subroutines (sub-routines after END)
External functions (functions after END)
TODO: Library support
TODO: Module support

Currently supported types of parameters for subroutines and functions:

numeric
string
numeric array
string array

BASIC statements

SUB
- EXIT SUB
- END SUB
- CALL
DATA
- READ
- MORE DATA
- RESTORE
DIM
DO
- DO WHILE
- DO UNTIL
- EXIT DO
- LOOP
- LOOP UNTIL
- LOOP WHILE
END
FOR
- EXIT FOR
- NEXT
GOTO
IF THEN
- ELSEIF THEN
- ELSE
- END IF
LET
PRINT
- PRINT;
- PRINT ;
- PRINT ,
- TODO: add support for MARGIN or ZONEWIDTH
- TODO: add support for TAB() function
SELECT CASE
- CASE
- CASE ELSE
- END SELECT

Built-in functions

STR$
INT

Operators:

Conditional operators

AND
OR

Numeric operators:

Arithmetic operators: + - / * ^
Relational operators: = < <= > >=

String operators

Concat: &
Substrings:
- LET s$ = "XXXhelloXXX"[4:8]
- LET s$[1:1] = "B"

vintzend

As can be seen above, this week I implemented all DATA related BASIC commands:

DATA
READ
MORE DATA
RESTORE

This can now be executed (after compiling to TRC):

FOR I = 1 TO 5
	PRINT
	PRINT "#" & STR$(I)
	DO WHILE MORE DATA
		READ BLA$
		PRINT BLA$
	LOOP
	
	RESTORE
NEXT I

DATA "a", "bee", "C""", "D,,,,", "E"",", 1234

END

vintzend

Worked last few weeks (on and off) on supporting routines.

First one I got working are internal subroutines (before the END statement): SUB, END SUB, CALL, EXIT SUB.

This code does now work (once compiled to TRC by a 5.5 or 6.0 True BASIC compiler):

LET A = 30
CALL TESTRECURSIVE(A)

SUB TESTRECURSIVE(N)
	PRINT N
	IF N = 0 THEN 
		CALL BYEBYE
		EXIT SUB
	END IF
	CALL TESTRECURSIVE(N - 1)
END SUB

SUB BYEBYE
	PRINT "Ciao!"
END SUB

END

I expect some problems with scopes, but so far all me tests have been successful (much to my own surprise). This will need a lot of additional testing.

If I don't find any errors, I expect adding support for internal functions will be relatively easy now.

The next things I'll try to tackle will look something like:

Add support for internal functions
Add support for external subroutines and functions (after END statement)
Add support for libraries (links to external TRC files)
Add support for directory aliases (needed for libraries)
Add support for modules

vintzend

I hope updates are appreciated.

If not, please let me know.

One more thing: I've tried compiling above's program in the True BASIC for DOS version 3 compiler,, the download that I bought from True BASIC web store, and its output also ran fine in my interpreter.

vintzend

Last week I've implemented support for internal functions (functions before END). The last few days I've worked on adding external subroutines (SUB/END SUB after END) and external functions (functions after END).

So all kinds of procedures are now supported, IF they are defined directly in the main program file.

Only supported parameters for now are numeric, strings, numeric arrays and string arrays.

My roadmap will look like something like this:

Add support for libraries (functions and subroutines in library TRC files)
I'll try to add as many missing commands to get at least one of my favorite supplied libraries of TB Silver fully (or mostly fully 🙃 ) working, so I can test everything much better
Add support for modules

After that is finished I'll start working on I/O, especially text and binary files (OPEN, CLOSE, PRINT #1, "hello" etc.). Which will be a huge topic and require a lot of time.

If I can pull that off, this will also include implementing support for passing channel numbers to functions and subroutines.

mcc

Your work is very interesting. I'm not quite sure how your'e going about doing this, or exactly what it will be able to do once it is finished. But if it could lead to, or help with, updating the core code of True Basic, that would be great indeed. It surely needs being brought up to date in terms of adding features, such as dealing with multimedia, graphics, the "mouse-wheel" problem, etc., which essentially didn't exist when the thing was originally invented. I have often wondered if anyone has tried to hack the code with something like ghidra in order to get in and be able to work on adding new features.

The language is fine as it is, it just needs a few additional capabilities. I do hope you will continue to post your progress.
Regards,
Mike C.