java-tiny-basic

A Tiny BASIC parser, interpreter and transpiler (to Java bytecode) written in Java.

Note: This project is more-or-less very experimental and does not have no-where near complete support for the Tiny BASIC language. I.e., it's tokenisation process is very basic and not suitable for this language.

Features:

• Core Tiny BASIC language support
• Parser and interpreter
• Transpiler to Java bytecode (BETA)
  • very rudimentary and not fully functional
  • if statements are prone to breaking due to the contrast in handling of control flow in Java vs Tiny BASIC
• TODO Unit tests for parser and interpreter
• TODO JavaDoc documentation for all public classes and methods

Usage

Parser

import me.darragh.javatinybasic.ast.Token;
import me.darragh.javatinybasic.parser.Parser;
import me.darragh.javatinybasic.parser.ParserInvalidLineException;

import java.util.List;

public class ParserDemo {
    public static void main(String[] args) throws ParserInvalidLineException {
        List<Token> tokens = Parser.parse("""
            10 REM This is a comment
            20 LET A = 5 + 5
            30 LET B = 10
            40 PRINT "A + B =", A + B
            50 INPUT C
            60 PRINT C
            70 END
            """);
        for (Token token : tokens) {
            System.out.printf("%s\t%s\t%s%n", token.lineNumber(), token.statement(), token.expression());
        }
    }
}

View Example

Interpreter

import me.darragh.javatinybasic.ast.Token;
import me.darragh.javatinybasic.interpreter.Interpreter;
import me.darragh.javatinybasic.parser.Parser;
import me.darragh.javatinybasic.parser.ParserInvalidLineException;

import java.util.List;
import java.util.Scanner;

public class InterpreterDemo {
    public static void main(String[] args) throws ParserInvalidLineException {
        Scanner scanner = new Scanner(System.in);
        List<Token> tokens = Parser.parse("""
                10 LET A = 5
                20 LET B = 10
                30 PRINT "Initial A and B:", A, B
                40 INPUT C
                50 IF C > B THEN 80
                60 PRINT "C is less or equal to B"
                70 GOTO 90
                80 PRINT "C is greater than B"
                90 FOR I = 1 TO 3 STEP 1
                100 PRINT "Loop iteration:", I
                110 NEXT I
                120 GOSUB 150
                130 PRINT "Back from subroutine"
                140 END
                150 PRINT "In subroutine"
                160 RETURN
            """);
        Interpreter interpreter = new Interpreter(tokens,
                /* input */ scanner::nextInt,
                /* output */ System.out::println,
                /* finished */ () -> System.out.println("Finished!")
        );
        interpreter.run();
        scanner.close();
    }
}

View Example

Transpiler

⚠️ Unstable.

import me.darragh.javatinybasic.ast.Token;
import me.darragh.javatinybasic.parser.Parser;
import me.darragh.javatinybasic.parser.ParserInvalidLineException;
import me.darragh.javatinybasic.transpiler.Transpiler;

import java.nio.file.Paths;
import java.util.List;

public class TranspilerDemo {
    public static void main(String[] args) throws ParserInvalidLineException {
        List<Token> tokens = Parser.parse("""
            10 LET A = 5
            20 IF A = 5 THEN 50
            30 GOTO 60
            50 PRINT "= PASS"
            51 GOTO 70
            60 PRINT "= FAIL"
            61 GOTO 70
            
            70 LET A = 5
            80 IF A <> 3 THEN 110
            90 GOTO 120
            110 PRINT "<> PASS"
            111 GOTO 130
            120 PRINT "<> FAIL"
            121 GOTO 130
            
            130 LET A = 2
            140 IF A < 3 THEN 170
            150 GOTO 180
            170 PRINT "< PASS"
            171 GOTO 190
            180 PRINT "< FAIL"
            181 GOTO 190
            
            190 LET A = 7
            200 IF A > 3 THEN 230
            210 GOTO 240
            230 PRINT "> PASS"
            231 GOTO 250
            240 PRINT "> FAIL"
            241 GOTO 250
            
            250 LET A = 4
            260 IF A <= 4 THEN 290
            270 GOTO 300
            290 PRINT "<= PASS"
            291 GOTO 310
            300 PRINT "<= FAIL"
            301 GOTO 310
            
            310 LET A = 6
            320 IF A >= 6 THEN 350
            330 GOTO 360
            350 PRINT ">= PASS"
            351 GOTO 370
            360 PRINT ">= FAIL"
            361 GOTO 370
            
            370 FOR I = 1 TO 5 STEP 1
            380 PRINT I
            390 NEXT I
            400 END
            """);
        Transpiler transpiler = new Transpiler(tokens);
        transpiler.toFile(Paths.get("example.jar"));
    }
}

View Example

Syntax

{line number}   REM {comment (ignored line)}
{line number}   LET {variable} = {expression (current value of variable|literal number|arithmetic expression)}
{line number}   PRINT {expression (current value of variable|literal number|arithmetic expression|"string")}, {...}
{line number}   INPUT {variable}
{line number}   IF {expression (current value of variable|literal number|arithmetic expression)} {comparison operator} {expression (current value of variable|literal number|arithmetic expression)} THEN {line number}
{line number}   FOR {variable} = {expression (current value of variable|literal number|arithmetic expression)} TO {expression (current value of variable|literal number)} STEP {expression (current value of variable|literal number)}
{line number}   NEXT {variable}
{line number}   GOTO {line number}
{line number}   GOSUB {line number}
{line number}   RETURN (exits out of the GOSUB)
{line number}   END

This attempts to be faithful to the original Tiny BASIC syntax, but may not support all features or edge cases. The parser is designed to be simple and easy to understand, so it may not handle all possible syntax errors gracefully.

Comparison Operators

=   EQUAL
<>  NOT_EQUAL
<   LESS_THAN
>   GREATER_THAN
<=  LESS_THAN_OR_EQUAL
>=  GREATER_THAN_OR_EQUAL