Interpreter for Genshi BASIC; A simple dialect of BASIC created to learn the basics of making a programming language.

Even though writing an interpreter for a custom BASIC dialect is pretty useless, the same lexing, parsing, and interpreting fundamentals I learned can be applied to other languages.

I originally wrote this in 2019, but decided that this year (2021) I would rewrite it to practice concepts I had learned since the original implementation.

I did get kind of lazy and skipped out on implementing a REPL, so for right now it justs interprets an array of strings or a source file.

Genshi BASIC has 41 keywords. As stated above, the grammar is based on BASIC version 2.

Genshi (原始) means "simple" in romaji. I chose this name because I stripped out a lot of functionality to make a simpler BASIC. Arguably this makes it pretty useless, but this is a learning project rather than a useful one.

Its worth noting that this is not fully tested. I more or less got a couple programs working correctly and called it a day. As I said before, this is a rewrite and I'm honestly very bored of it now.

Genshi BASIC is meant to be a simpler version of BASIC version 2. I stripped out a bunch of stuff and didn't really add anything special.

I used this page on Commodore 64 commands as reference for BASIC version 2.

Removed:

• function declarations - DEF, FN
• memory operations - FRE, PEEK, POKE, WAIT, NEW
• system operations - GET, STATUS, SYS, USR, TIME
• file operations - OPEN, LOAD, CLOSE, VERIFY, SAVE
• "interactive" operations - RUN, STOP, LIST

Changed:

• string variables are no longer required to end with '$'
• removed '$' characters from CHR$,LEFT$,MID$,RIGHT$ operations

Added:

• new keywords - XOR
• I lost motivation to add anything else cool

# Usage of genshi BASIC interpreter

from genshibasic.interpreter import Interpeter

pgm = [
  '10 REM Example 1',
  '20 LET A=3+4 * 6/2',
  '30 PRINT "A="; A',
  '40 A=8',
  '50 PRINT "NOW A="; A',
  '100 END'
]

genshi_int = Interpeter()
genshi_int.interpret(pgm)
    
# A=15.0
# NOW A=8

• Install deps - pip3 install -r requirements.txt
• Run tests - python3 -m unittest discover

• Commodore 64 BASIC
  • https://www.c64-wiki.com/wiki/BASIC
  • https://www.c64-wiki.com/wiki/C64-Commands
• EBNF https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form