MilliForth-6502 is a minimalist Forth implementation for the 6502 processor, designed to be incredibly small while remaining a practical programming language. It features a 1 KB dictionary, a 256-byte parameter stack, and implements core Forth words including arithmetic, logic, stack manipulation, and I/O. Despite its size, MilliForth allows for defining new words and includes a simple interactive interpreter. Its compactness makes it suitable for resource-constrained 6502 systems, and the project provides source code and documentation for building and using it.
MilliForth-6502 is presented as an incredibly compact implementation of the Forth programming language, specifically designed for the 6502 microprocessor, a popular 8-bit processor used in systems like the Apple II, Commodore 64, and Atari 8-bit computers. The project's primary goal is to create a functional Forth system within an extremely limited memory footprint, aiming for a size under 1 kilobyte. This makes it suitable for resource-constrained environments or as a foundational layer for building more complex software on 6502-based platforms.
The core features of a traditional Forth system are retained, including a dictionary (a symbol table that maps words to their corresponding code), an interpreter for executing Forth words, and a compiler for defining new words. MilliForth-6502 utilizes a threaded interpretation model, where each word's definition consists of a sequence of pointers to other words, creating an efficient execution flow.
The system provides a minimal set of primitive words, allowing for basic arithmetic, logical operations, stack manipulation, memory access, and input/output functions. These primitives serve as the building blocks for creating more complex words and programs through Forth's unique approach to programming, which relies heavily on combining smaller, defined words into larger, more specialized words.
A key aspect of MilliForth-6502's design is its simplicity. The code is meticulously crafted to minimize its size while maintaining functionality. This minimalistic approach is not just about conserving memory but also about providing a clear and understandable implementation of Forth, making it a valuable resource for learning or exploring the inner workings of both Forth and the 6502 architecture. The source code is provided for users to examine, modify, and adapt to their specific needs.
While complete, MilliForth-6502 acknowledges its own limited nature. It is a foundational system designed for expansion. Users are expected to build upon the core functionalities and extend the vocabulary with custom words tailored to their particular applications. It provides a compact and robust basis for further Forth development on the 6502 platform.
Summary of Comments ( 2 )
https://news.ycombinator.com/item?id=43503897
Hacker News users discussed the practicality and minimalism of MilliForth, a Forth implementation for the 6502 processor. Some questioned its usefulness beyond educational purposes, citing limited memory and awkward programming style compared to assembly language. Others appreciated its cleverness and the challenge of creating such a compact system, viewing it as a testament to Forth's flexibility. Several comments highlighted the historical context of Forth on resource-constrained systems and drew parallels to other small language implementations. The maintainability of generated code and the debugging experience were also mentioned as potential drawbacks. A few commenters expressed interest in exploring MilliForth further and potentially using it for small embedded projects.
The Hacker News post for MilliForth-6502 has a modest number of comments, focusing primarily on its size, speed, and potential applications.
Several commenters express fascination with the extreme minimalism of MilliForth, marveling at how a functional Forth system can be implemented in such a small footprint. They discuss the challenges and ingenuity involved in fitting a complete language within such tight constraints. Some commenters delve into the technical details of its implementation, analyzing how certain features are achieved with limited resources.
A recurring theme is comparing MilliForth to other small language implementations, particularly FORTHs and BASICs on similar hardware. Commenters share anecdotes and experiences with historical systems, highlighting the tradeoffs between size, speed, and functionality. Some discuss how MilliForth's size compares favorably to other FORTHs on the 6502, while acknowledging that its minimalist nature may impact usability for larger projects.
The speed of MilliForth is also a point of discussion. Some commenters question its performance relative to other FORTHs and even assembly language, wondering if the extreme size optimization comes at the cost of execution speed. Others express interest in benchmarking MilliForth against similar systems to quantify its performance characteristics.
Regarding applications, some commenters speculate on potential uses for such a small FORTH, suggesting embedded systems, retrocomputing projects, and educational purposes as possible areas where MilliForth could be valuable. The idea of fitting a complete language within the limited memory of older hardware is particularly appealing to retrocomputing enthusiasts. One commenter mentions using a similar small FORTH on an Apple II, demonstrating the practicality of such systems.
Finally, a few comments focus on the readability and maintainability of the code. Due to its highly optimized nature, some commenters acknowledge that MilliForth might be challenging to understand and modify. However, the overall sentiment leans towards appreciation for the technical achievement, even if the code itself is not intended for extensive modification.