BASIC Interpreter

A BASIC interpreter written in Python. Reads .bas files, tokenises them, parses the commands, and runs them. No classes, no external libraries. Just functions calling functions.

What you need

Python 3

Quick start

Pass a test file and run it:

python3 src/main.py tests/test_print.bas

You'll see the output right in your terminal. The interpreter prints RUN, executes your program line by line, then prints END when it finishes or hits an END statement.

What it supports

The usual BASIC stuff. Nothing fancy.

Variables and maths

10 LET X = 5
20 LET Y = X * 2 + 1
30 PRINT Y

Printing things

10 PRINT "Hello"
20 PRINT "The value is "; X

Semicolons keep output on the same line. Without them you get a newline. Strings go in double quotes.

User input

10 PRINT "Enter a number"
20 INPUT X
30 PRINT "Twice that is "; X * 2

Loops

10 FOR I = 1 TO 10
20 PRINT I
30 NEXT I

FOR loops count up. The loop variable increments by 1 each time. NEXT jumps back to the line after the FOR statement.

Conditions

10 IF X > 5 THEN PRINT "Big"
20 IF Y = 0 THEN GOTO 100
THEN can run a PRINT, a GOTO, or a LET. Simple comparisons only: =, >, <, >=, <=.

Jumping around

10 GOTO 50
20 PRINT "Skipped"
50 PRINT "Here"

Every line needs a line number. GOTO jumps to that number. Labels aren't supported, use line numbers instead.

Comments

10 REM This does nothing
REM lines get ignored. Useful for leaving notes.

Running the test suite

cd tests
./run_tests.sh

This will print a pass/fail for each test.