Visualizing programs with side-effects in a postfix shell with a live-updating text-mode environment. Built all the way up from machine code without any dependencies (except an x86 processor and Linux kernel).


Project page: github.com/akkartik/mu

More context: mastodon.social/@akkartik/1048

*Editing functions in the Mu shell*


Long delay since my last video. Printing floating-point numbers is *really* hard. I'm still half-assing it.

As a follow-up to merveilles.town/@akkartik/1053, I'm tightening focus to two threads:

a) These Mu shell experiments, and
b) An extremely skeletal OS to drop the Linux kernel dependency.

Deprioritized for now:
a) Other processors: RISCV, ARM, RPi, etc.
b) Graphics, mouse, etc. Device priorities for the OS are disk then ethernet.

*Towards running Mu without Linux*

All Mu really needs so far is to print to screen and read from the keyboard. Here's a 2-minute video about achieving that:


It seems such a small thing. But I needed lots of help, as you can see from the additions to my credits: github.com/akkartik/mu/compare

Merry Christmas to all! What a beautiful world.

Project page: github.com/akkartik/mu

More context: mastodon.social/@akkartik/1048

*Switching gears to pure graphics*

Until now Mu has followed classic Unix: stdin, stdout, pure text mode.

But giving up an OS kernel requires controlling the screen myself. Which requires various complicated probing for hardware. Then programs handling various screen sizes.

Easier: just always assume some common graphics mode. Say 1024x768 with 256 colors.

Interestingly, the default palette has far fewer than 256 colors. (Pic: 1024 cols each contain color `col%256`.)


*2020: Flood-filling the Mu computer*

A year ago I had a prototype of a C-level programming language mapping 1:1 to Assembly that I _thought_ could be type-safe.

Since then, I:

* wrote an academic paper on it
* made it type-safe
* began a high-level language atop it
* got into video, with 15 2-minute screencasts
* and ran programs written in it on bare metal, without an OS, like, 5 years before I expected to.

❤️ to everyone who inspired, taught, debated, encouraged.


*Rendering text atop baremetal*

Mu can now render text atop baremetal x86.

Try clicking around from akkartik.github.io/mu/html/bar

The boot-up machine code reads a few sectors from disk, configures a keyboard handler, and loads a bitmap font (2KB for ASCII, with the option for more).

I use GNU Unifont. I believe that means Mu is now GPL v2. So stated. IANAL and I try not to think about software IP. But a font? Copyright seems reasonable there.

Next up: a text editor!


*A more international interface for rendering text*

New 2-minute video: archive.org/details/akkartik-2

You get just one fixed screen resolution: 1024x768, 256 colors. Widely available on modern machines, no drivers needed.

You get just one fixed-width bitmap font. No bold/italics, no anti-aliasing.

BUT it won't make assumptions about English and left-to-right order. I eventually want anybody to be able to customize it to their language.

Main project page: github.com/akkartik/mu

I've been trying to visualize the default 256-color palette I get on baremetal.


To my eyes it looks like I can/should just live in the first 128 colors.

I built a game of "snakes", but it came out more like an etch-a-sketch 😄


Play it on any non-windows:

git clone github.com/akkartik/mu
cd mu
./translate_mu_baremetal_emulated baremetal/ex7.mu
qemu-system-i386 disk.img

h/j/k/l to draw

It took a while, but I've finally ported a pre-existing Mu program to baremetal: an RPN calculator.

This was _hard_, purely because of cursor management. I have a greater appreciation for everything that display hardware and terminal emulators provide for text mode. Mu so far puts the onus on the programmer.


In the end it's interesting to visualize the changes I had to make:

vim -d apps/rpn.mu baremetal/rpn.mu

They're entirely in `main`; the rest is unchanged.

I've been reimplementing my from-scratch live-updating postfix shell to _really_ from scratch (no more OS kernel), while at the same time rewriting the prototype with lots of tests and actually giving the language some sort of rigorous basis. No demos yet, but in the meantime here's Conway's Game of Life running on baremetal Mu.


Sources: akkartik.github.io/mu/html/bar

Main project page: github.com/akkartik/mu

The Mu shell is now off Linux


Starting point for the sources: akkartik.github.io/mu/html/bar

The architecture is now much cleaner. Functions contain lines, lines contain words, words contain gap buffers. Rendering a thing renders its constituent things. Render takes a top-left coordinate and returns a bottom-right coordinate. Each thing knows which constituent thing has its cursor, shows its cursor when rendering, redirects incoming keystrokes to it.


An experimental way to do control flow in the postfix Mu shell

The screenshot below shows an idea I've been playing with.

The conventional way Forth does control flow is a little confusing with words like `if` and `then` showing up at the end.

Factor uses quotations to put code blocks on the stack. But then you see a potentially complex chunk of code executing "all at once".

Main project page: github.com/akkartik/mu

Drilling into computations on the Mu shell

This was one of the more difficult things I've built, and yet all I've gotten working so far is some rudimentary tokenization. The reason is one little feature.. well, take a look for yourself.

archive.org/details/akkartik-2 (video; 2 mins)

As always, built all the way up from machine code, and designed primarily to be easy to build, easy to run, comprehensible to others. Also this time with lots of tests


Today was documentation day

Primitives available in the Mu computer when running without an OS: github.com/akkartik/mu/blob/ma

Primitives available when running on Linux: github.com/akkartik/mu/blob/ma

For starters I focused just on making things more discoverable. These files are optimized for opening in your text editor, jumping to definitions to see type signatures, etc. See github.com/akkartik/mu/blob/ma for a ctags configuration for Mu and SubX programs.

Main project page: github.com/akkartik/mu

Mu can now read from an ATA (IDE) disk drive on Qemu.


It wouldn't have been possible without the lovely folks over on . And the inspiration of ColorForth (merveilles.town/@akkartik/1059), though I still don't understand how that driver works.

The Mu computer now has drivers for disk and mouse.

Still extremely klunky. IDE disk drives only, and the mouse driver uses polling because configuring IRQ 12 is still beyond me.

Example programs (as usual memory safe and translating 1:1 to x86 machine code)

Disk: akkartik.github.io/mu/html/ex9

Mouse: akkartik.github.io/mu/html/ex1

Here's video of the mouse example. There's no pointer so you have to imagine me moving the mouse around.

Like I said. Klunky.

Main project page: github.com/akkartik/mu

What should the signature of a program look like?

Typed languages have a fixed signature for function `main`. A list of strings, a window context, or an IO monad.

Here's the signature on the Mu computer:

fn main screen: (addr screen), keyboard: (addr keyboard), data-disk: (addr disk)

A rudimentary, hokey capability system. No mouse yet. 'screen' is only used for text; pixel graphics currently go around it. 'data-disk' can't access code, and will eventually include finer-grained restrictions.

Mu's HLL is now Turing-complete, I think.

Things to notice:
* Wordstar-style menu at the bottom.
* List of available primitive functions in bottom left.
* List of globals on the left side that updates as I add definitions.
* Matching parens highlighted as I type.
* Drilling down into the trace to understand how the program was evaluated.


Main project page: github.com/akkartik/mu

Prototyping on the Mu computer

A 3-minute video showing what it's currently like to prototype programs on the Mu computer. There are lots of limitations. It's slow, and it can only handle short runs.

While these limitations will be relaxed over time, the goal is partly to nudge people to throw the prototype away once they know what they want, and rewrite it one level down. Therefore: encourage people to write lots of tests.


Main project page: github.com/akkartik/mu


Managing side-effects on the Mu computer

archive.org/details/akkartik-m (video; 2 minutes)

The Mu computer's prototyping environment uses _traces_ to explain and debug programs. But traces are expensive to compute and made the environment slow and laggy.

I fixed things by collecting only a shallow trace at first, and iteratively deepening on demand by rerunning programs. This only works because it's safe to rerun functions. There are no side-effects in Mu.

Main project page: github.com/akkartik/mu

· · Web · 2 · 4 · 6

Some live-coding in my programming environment, running on my computing stack built up from scratch.

archive.org/details/akkartik-m (video; 6 minutes)

Main project page: github.com/akkartik/mu

Collaborating on a problem from Advent of Code in Mu

If anybody is into long and rambling 100-minute videos that taper off without a certain conclusion:


Mostly by Sumeet Agarwal (github.com/sumeet)

Here's the working solution if anyone wants to try it out it: akkartik.github.io/mu/html/lin

Main project page: github.com/akkartik/mu

Syntax sugar in the Mu shell

I like Lisp. But I also strongly believe anyone should be able to boot into a computer and immediately type in '1+1'. Get started using the computer as just a calculator. It's surprising how few computers satisfy that property. Now the Mu computer does.

archive.org/details/akkartik-m (video; 8 minutes)

Main project page: github.com/akkartik/mu

Starting to render images on the Mu computer

This screenshot shows a greyscale image dithered using just black and white pixels.

I rather suspect this isn't quite right. There are some suspicious streaks in various places. Rounding error, maybe.

Credit: tannerhelland.com/2012/12/28/d. I'm using standard Floyd-Steinberg.

Main project page: github.com/akkartik/mu

Generalizing dithering to color (assuming a fixed palette) turns out to be surprisingly complex. The r/g/b channels are mostly independent copies each analogous to the greyscale dither, but there's tangling in one place in the center that complicates everything.

I was just reminded after years of the "weird number" in 2's complement arithmetic: en.wikipedia.org/wiki/Two%27s_

The reason it came up: it's the result of trying to convert a floating-point Infinity or NaN to an integer.


Color dithering on the Mu computer.

Here is a before/after pair of images. Before has 256x256x256 colors. After has 256 colors.

Notice all the yellow pixels in the first image that turn into alternating greens and oranges in the second. Also, the stem looks very different. But overall, it looks gratifyingly similar to the original. My eyes took a while before they started to notice differences.

Main project page: github.com/akkartik/mu

A little game: guess the result of mixing two colors

Testimonial from 4 year old: this is the best program you've made.

Source: akkartik.github.io/mu/html/app

Main project page: github.com/akkartik/mu

Images (kinda) and files (kinda) on the Mu computer

The Mu computer has only 256 colors by default, but approximates arbitrary RGB combinations using dithering.

archive.org/details/akkartik-m (video; 9 minutes)

Main project page: github.com/akkartik/mu

A network-less, read-only browser built up from machine code

archive.org/details/akkartik-m (video; 5 minutes; includes instructions to try it out)

A lot gets said about simplicity in software, about essential vs accidental complexity. If you really want a simple stack that empowers everyone, it isn't enough to just eliminate accidental complexity (even if we could all agree on what it is). You need to also avoid _other people's_ essential complexity.

Main project page: github.com/akkartik/mu

The Mu computer now loads 140KB of Unicode glyphs from its system font

Unicode blocks now supported: latin, greek, cyrillic, armenian, hebrew, arabic, syriac, thaana, n'ko, indian (ISCII), sinhala, thai, lao, tibetan, myanmar, georgian (< U+1100)

- No support for combining characters yet (en.wikipedia.org/wiki/Combinin) This makes the other languages I know (Hindi, Tamil) well-nigh useless.

- Unifont's glyphs for the non-Latin languages I know turn out to be quite spectacularly ugly.

Hackiest possible support for rendering Unicode combining characters using GNU Unifont

This is the equivalent of backing up a typewriter by one character and overlaying a second letter on the same space.

Main project page: github.com/akkartik/mu

@nasser following up on merveilles.town/@akkartik/1057 from six months ago, I think Mu is now at approximately the level of mediocrity/trashiness of conventional software when it comes to rendering Arabic. Likely still worse, but I mean they probably both suck to you 😄

I have a hazy plan now to construct a trie data structure that maps utf-8 byte prefixes to glyphs (which can have arbitrary-size bitmaps) Read one byte at a time into a buffer, select the glyph for the longest prefix. What do you think?

@akkartik Hell ye, I've been waiting to see someone use functional purity this way! Another use case I've been considering and hope to explore one day is for caching and handling OOM conditions gracefully. If you know that a result is relatively cheap to compute again, you can just drop it and let other computations finish.

@akkartik looks like the error isn't diffusing! definitely not quite right for Floyd Steinberg.

@akkartik here's a Floyd Steinberg implementation of that image at about 400 pixels wide

@oppen Thanks! Yeah you're right. Here's what I get for a 16x16 image where every pixel is at level 128 of 0-255 levels of grey. Definitely doesn't look right past the first row of pixels.

"The diffusion coefficients have the property that if the original pixel values are exactly halfway in between the nearest available colors, the dithered result is a checkerboard pattern."


@oppen I wonder if it's the >>4 to simulate /16. Introduces some error. On the other hand it seems designed to not need division.

@oppen Looking better.

Every time I mutate a function's args, I live to regret it.

@oppen _Now_ giving it more precision yields a perfect checkerboard pattern.

@akkartik couldn’t this be simplified by forgetting about the different colour channels and defining error and colour to be a vector type from the start? then it doesn’t matter if it’s rgb or lab or grayscale except in the error function itself?

@akkartik then the error you diffuse is a vector quantity and, handling each dimension seperately becomes something for the compiler to deal with?

@akkartik particularly since error as you have here becomes a manhattan distance, not a euclidean distance as you might prefer- or better, a CIE delta_E function

@zens Well, there's no compiler here but what I've written 😄 You're right that I'm trying to implement a vector computation for myself that generalizes the single dimension of greyscale.

It's not Manhattan distance, though. The 'nearest' box is hiding a Euclidean measure which decomposes into the error arrays.

A different scale may well work better. I don't really know what I'm doing there. I built a nearest out of HSL but took it out. It's a cylindrical space so Euclidean doesn't seem right.

@zens Part of the problem is that en.wikipedia.org/wiki/Floyd%E2 adds errors into the input array. But input pixels have different ranges from errors. 1-byte ints vs fractions. So I've been tracking errors in a separate array.

A = input pixel + error
B = nearest pixel to A
C = error - B
Diffuse C to neighboring pixels

Perhaps there's a better way.

@akkartik my thinking lately has been this: most/all dithering algorithms were invented under the assumption that users expect extremely low 1980s era memory requirements, so only a few pixels are held in memory at a time. if you can hold all pixels in memory, error could be diffused in all directions iteratively.
step1. threshold work image
step2. error image is diff of threshold with original
step3. modify error image with diffuse(img)
step4. error image + original = work

@akkartik that said, there’s other benefits to dither algorithms that run streaming and in a single pass, just saying we are no longer limited to these

@zens Fascinating! Definitely worth researching. For now I just want to be able to display arbitrary images, say from Wikipedia, even though I have only 256 colors.

@akkartik i remember @makeworld had very interesting findings related to color when developing their dithering library a couple of months ago!

@chirrolafupa Indeed. There were a couple of blog posts a few months ago that had serendipitous timing for me (+- a few months) @makeworld

@akkartik :tealheart: lovely testimonial!
from what i've seen from your work, i disagree with them ^^, but it does make me think about different priorities in life and about being relatable (or not) when creating "esoteric" worlds

@akkartik of course until the unicode is displayed it is in a superposition of both Shr00fdinger and Shrödinger

@akkartik That metaphor reminds me of an idea I came up with last year.

The invention of writing has usually involved etching/pushing/brushing pigments upon a substrate. But what if a writing system was invented based on stamps? A scribe might angle and directionally smudge the same stamp in different ways to make different glyphs.

And then maybe they could go back and overlay more stamps on top of what they wrote to encode more detail.

Voila, a writing system with LOD based on overstrike! 🤓

@akkartik i am not sure i follow -- how do utf8 prefixes solve the shaping problem? you have to turn eg the byte sequence (read from right to left)
م ر ح ب ا
when you encounter م how do you know, from prefix alone to render مـ? same for ر being rendered as ـر, and so on?

@nasser Basically unbounded lookahead. I'm wondering if you can just throw more glyphs at the problem for lots more combinations of utf-8 bytes, far more than the usual 4 or 6. If you don't yet know which of n ways to render a glyph, just keep reading.

@nasser In this case I'd have a glyph for

م ر

which looks like


@akkartik I worry that gets you into a situation where you basically need a separate "glyph" for each word? for example
م س ت ق ب ل ن ا
should render as
rendering م on its own is wrong, مس is wrong, مست is also wrong, مستق also wrong... and so on, until I get to the end of the word, which is what needs to be rendered, and if I understand the system correctly there needs to be a single glyph for that. is that accurate? if so then you are facing a combinatorial explosion of "glyphs"

@akkartik fwiw conventional text shaping avoids a combinatorial explosion by breaking up cursive letters into four forms, initial medial final and isolated. The shaping engine then selects and positions the correct form for each letter based on its position in the word and a state machine that it maintains. ope type has facilities to replace runs of characters with a ligature (which is sort of what your system is doing), but the default shaping algorithm does not depend on this.

@nasser @akkartik i have always wondered if arabic text needed more of an approach like knuth’s metafont- e.g. instead of drawing closed bezier shapes, do more of an actual pen calligraphy simulation, where letter joins happen as a result of virtual pen movement. it’s more complicated but maybe justified complexity?

@zens @akkartik I feel similarly. this is something I've wanted to play around with for a while.

@nasser @zens @akkartik I have seen vistages of this still present in Cairo Vector Graphics. Though now they've fully switched to heavily-optimized character-by-character blitting.

Seems like there needs to be new Arabic font formats for it to be worth sticking with this vector approach...

@alcinnz @nasser @akkartik postscript fonts when they were still a thing were full postscript programs. they could possibly have handled this

@alcinnz @nasser @akkartik at the very least, brush simulation or not, it seems that these scripts require more flexible constraint primitives than mere blitting of precachef shapes could provide

@nasser What about the ambigram examples I've seen? Is that a separate style with its own rules?

Sign in to participate in the conversation

Revel in the marvels of the universe. We are a collective of forward-thinking individuals who strive to better ourselves and our surroundings through constant creation. We express ourselves through music, art, games, and writing. We also put great value in play. A warm welcome to any like-minded people who feel these ideals resonate with them.