xbasic64

A BASIC-to-x86_64 native code compiler.

Overview

xbasic64 compiles 1980s-era BASIC dialects (Tandy Color BASIC, GW-BASIC, QuickBASIC) directly to native x86-64 executables. No interpreter, no bytecode—just fast native binaries.

Why xbasic64?

• Nostalgia: Write and run classic BASIC programs on modern hardware
• Education: Learn compiler design with a simple, readable Rust codebase
• Simplicity: Direct AST-to-assembly compilation with no intermediate representation

Features

• Classic BASIC syntax with line numbers or structured code
• Numeric types: Integer, Long, Single, Double (with type suffixes)
• String handling with standard functions (LEFT$, MID$, etc.)
• Control flow: IF/THEN/ELSE, FOR/NEXT, WHILE/WEND, DO/LOOP, SELECT CASE
• Procedures: SUB and FUNCTION with recursion support
• File I/O: Sequential file reading and writing
• DATA/READ/RESTORE for inline data
• Full expression support with proper operator precedence

Quick Start

Building

cargo build --release

Usage

# Compile a BASIC program to executable
xbasic64 program.bas

# Specify output file
xbasic64 program.bas -o myprogram

# Emit assembly only (no linking)
xbasic64 -S program.bas

Example

' Fibonacci sequence
A = 0
B = 1
FOR I = 1 TO 10
    PRINT A
    C = A + B
    A = B
    B = C
NEXT I

Save as fib.bas, compile with xbasic64 fib.bas, and run ./fib.

Documentation

• Language Reference - Complete guide to the supported BASIC dialect
• Design Specification - Internal compiler architecture and design decisions

Architecture

The compiler uses a three-stage pipeline:

Source → Lexer → Parser → Code Generator → Assembly → Executable
              (tokens)   (AST)          (x86-64)

1. Lexer - Tokenizes BASIC source (case-insensitive keywords, line numbers, type suffixes)
2. Parser - Recursive descent parser producing an AST
3. Code Generator - Direct AST-to-x86-64 assembly translation

The runtime library provides I/O, string operations, and math functions as hand-written x86-64 assembly using libc for portability.

Key design choices:

• No IR—direct AST to assembly for simplicity
• System V AMD64 ABI for libc interoperability
• GW-BASIC type semantics (division always returns Double)

Requirements

• Rust toolchain
• System assembler (as)
• System C compiler/linker (cc) with libc

Platforms

• macOS (x86-64, ARM64 via Rosetta)
• Linux (x86-64)

License

MIT