# Forth Interpreter in C

A minimal Forth interpreter written in C. This project implements a subset of the Forth programming language using a threaded-code architecture with separate data and return stacks.

## What This Is

This is a toy/subset Forth interpreter designed for educational purposes. It provides an interactive REPL where you can define words, manipulate the stack, and execute built-in primitives.

## How It Works

- **Threaded Code**: The interpreter uses an inner/outer interpreter model. Colon definitions are sequences of word addresses (threaded code) traversed by an instruction pointer.
- **Architecture**: 
  - 64-bit signed integer cells (`int64_t`)
  - Separate data and return stacks
  - Fixed-size dictionary, user memory, and compile buffer
  - Dictionary is a singly-linked list searched linearly
- **Supported Features**:
  - Stack manipulation (`DUP`, `DROP`, `SWAP`, `OVER`, `ROT`, etc.)
  - Arithmetic and logic (`+`, `-`, `*`, `/`, `MOD`, bitwise ops, comparisons)
  - Colon definitions (`: word ... ;`)
  - Variables and constants
  - Control flow (`IF ... ELSE ... THEN`, `BEGIN ... UNTIL`, `BEGIN ... WHILE ... REPEAT`)
  - Memory access (`@`, `!`, `C@`, `C!`, `HERE`, `ALLOT`)
  - Simple string output (`."`)
- **Limitations**:
  - Fixed user memory limit (1M cells); dictionary and stacks grow dynamically
  - 64-bit signed integers only; no floating-point support
  - No file I/O or operating system interface beyond stdin/stdout
  - No immediate user-defined words or advanced introspection
  - Single-threaded execution
  - Error handling is basic (prints message and often returns zero or ignores)

## Building

Run `make` to build the project. The resulting binary can be run directly for an interactive Forth session.

## Disclaimer

This project was written with the assistance of AI. It is provided as-is for educational and experimental use.