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What is muforth?

muforth is a small, simple, fast, indirect-threaded code (ITC) Forth intended for use as a cross-compiler for microcontrollers and other embedded devices. It is written in C and its core is very portable. Because of its Forth nature, it is naturally extensible, scriptable, and customizable.

It is very well-suited to interactive coding, debugging, and exploration, and is a great tool for bringing up new hardware.

It has support – in varying degrees of completeness – for the following architectures:

Why yet another Forth?

I initially wrote muforth because I wanted to try out some implementation ideas. Today there is very little that distinguishes muforth from fig-FORTH – but the differences go rather deep.

Its implementation is no longer the point. Its sole reason for existing is to be a cross/meta/target-compiler for other Forths, and their implementations are in no way tied to muforth’s.

It’s BSD licensed, so do what you want with it! I’d love to hear about innovative or unusual uses of muforth.

Starting points

BUILDING will tell you how to build muforth. It’s stupid simple.

Look in mu/target/ to find a target that interests you. There is generally a mu/target/<target-name>/build.mu4 that loads the cross-build environment. Use it as an “index” to find the assembler, disassembler, meta-compiler, kernel, and other key pieces of code.


Sadly, there isn’t a lot of documentation right now. A good place to start is to read the source.

The code – both the C code that implements the Forth virtual machine and the muforth code that does everything else – is carefully and in some cases extensively (even obsessively!) commented. Right now your best source of documentation is the code! Luckily for you, there isn’t that much, so reading it is actually possible. That’s part of the point of muforth; I want it to be a convivial tool.

The heart of the system is the Forth code that muforth reads when it first starts: mu/startup.mu4. You’ll learn a lot by reading this! is also, finally, spreading its wings.


In March 2008 I gave a talk about bootstrapping, muforth, and convivial tools.

Warning: I wave my arms around a lot, and the audio and video quality isn’t that great, but you might find it interesting, or at least amusing.

It’s also hard to see my slides. If you want to “follow along”, download my slides, and use less to view them – ideally in a text window that is about 31 lines high – like so:

less -G ~/muforth/talks/2008-mar-30-PNCA

Use /^=== to get to the second page, and n to page forward after that.

March 2008 talk on Vimeo

Above all, enjoy!


A simple, indirect-threaded Forth, written in C; for target compiling; runs on Linux, BSD, OSX, and Cygwin




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