Note: Folk is in a pre-alpha state and isn't yet well-documented or well-exampled.

We're making Folk's source code free and available to the public, in case you're already excited about trying it, but we haven't formally announced it or made it ready for public use. We make no guarantee of support, of usability, or of continuing backward compatibility. Try at your own risk!

We're working on a more formal announcement, which will talk more about the goals of the project & provide canonical examples/demos to show what's possible. If you don't know what this is, then you might want to wait for that release.

Folk

Folk is a physical computing system: reactive database, programming environment, projection mapping. Instead of a phone/laptop/touchscreen/mouse/keyboard, your computational objects are physical objects in the real world, and you can program them inside the system itself. Folk is written in a mix of C and Tcl.

Hardware

You'll need to set up a dedicated PC to run Folk and connect to webcam+projector+printer+etc.

We tend to recommend a Beelink mini-PC (or maybe a Pi 5).

See https://folk.computer/pilot/

Linux tabletop installation using live USB

Experimental: If you have an amd64 PC, you can use the live USB image which has Folk and all dependencies pre-installed.

See https://github.com/FolkComputer/folk/releases to get the Linux live USB image.

You can update Folk by running git pull in the folk subfolder of the FOLK-LIVE partition once you've flashed the live USB.

Manual Linux tabletop installation

On an Intel/AMD PC, set up Ubuntu Server 24.04 LTS (Noble Numbat).

(for a Pi 4/5, use Raspberry Pi Imager and get Raspberry Pi OS Lite 64-bit version [also see this issue if flashing from a Mac] -- Ubuntu doesn't have a good kernel for Pi 5)

Install Linux with username folk, hostname folk-SOMETHING? (check hosts.tcl in this repo to make sure you're not reusing one)

If no folk user, then:

 sudo useradd -m folk; sudo passwd folk;
 for group in adm dialout cdrom sudo audio video plugdev games users input tty render netdev lpadmin gpio i2c spi; do sudo usermod -a -G $group folk; done; groups folk

sudo apt update
Set up OpenSSH server if needed; connect to network. To ssh into folk@folk-WHATEVER.local by name, sudo apt install avahi-daemon and then on your laptop: ssh-copy-id folk@folk-WHATEVER.local
Install dependencies: sudo apt install rsync tcl-thread tcl8.6-dev git libjpeg-dev libpng-dev libdrm-dev pkg-config v4l-utils mesa-vulkan-drivers vulkan-tools libvulkan-dev libvulkan1 meson libgbm-dev glslc vulkan-validationlayers ghostscript console-data kbd

(When prompted while installing console-data for Policy for handling keymaps type 3 (meaning 3. Keep kernel keymap) and press Enter)
Vulkan testing (optional):
1. Try vulkaninfo and see if it works.
  1. On a Pi, if vulkaninfo reports "Failed to detect any valid GPUs in the current config", add dtoverlay=vc4-kms-v3d to the bottom of /boot/firmware/config.txt. (https://raspberrypi.stackexchange.com/questions/116507/open-dev-dri-card0-no-such-file-or-directory-on-rpi4)
2. Try vkcube:
```
git clone https://github.com/krh/vkcube
cd vkcube
mkdir build; cd build; meson .. && ninja
./vkcube -m khr -k 0:0:0
```
  If vkcube says Assertion ``vc->image_count > 0' failed, you might be able to still skip vkcube and continue the install process. See this bug
3. See notes and Naveen's notes.
sudo nano /etc/udev/rules.d/99-input.rules. add SUBSYSTEM=="input", GROUP="input", MODE="0666". sudo udevadm control --reload-rules && sudo udevadm trigger
Get AprilTags: cd ~ && git clone https://github.com/FolkComputer/apriltag.git && cd apriltag && make libapriltag.so libapriltag.a

Add the systemd service so it starts on boot and can be managed when you run it from laptop. On Ubuntu Server or Raspberry Pi OS (as root) (from here):

# cat >/etc/systemd/system/folk.service
[Unit]
Description=Folk service
After=network.target
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=1
User=folk
ExecStart=make -C /home/folk/folk

[Install]
WantedBy=multi-user.target

# systemctl start folk
# systemctl enable folk

Use visudo to add folk ALL=(ALL) NOPASSWD: /usr/bin/systemctl to the bottom of /etc/sudoers on the tabletop. (This lets the make scripts from your laptop manage the Folk service by running systemctl without needing a password.)

Then, on your laptop, clone this repository:

$ git clone https://github.com/FolkComputer/folk.git

And run make sync-restart FOLK_SHARE_NODE=folk-WHATEVER.local. This will rsync folk to the tabletop and run it there as well as running it on your laptop.

(or clone it onto the machine and run sudo systemctl start folk there)

How to control tabletop Folk from your laptop

On your laptop Web browser, go to http://folk-WHATEVER.local:4273 -- click New Program, hit Save, drag it around. You should see the program move on your table as you drag it around on your laptop.

Does it work? Add your tabletop to hosts.tcl! Send in a patch! Celebrate!

General debugging

You can run make journal to see stdout/stderr output from the tabletop machine. If you need to pass in a specific hostname, make journal FOLK_SHARE_NODE=folk-whatever.local.

make repl will give you a dialed-in Tcl REPL.

Printer support

On the tabletop:

$ sudo apt update
$ sudo apt install cups cups-bsd
$ sudo usermod -a -G lpadmin folk

(cups-bsd provides the lpr command that we use to print)

ssh tunnel to get access to CUPS Web UI: run on your laptop ssh -L 6310:localhost:631 folk@folk-WHATEVER.local, leave it open

Go to http://localhost:6310 on your computer, go to Printers, hopefully it shows up there automatically, try printing test page. I could not get that implicitclass:// automatically-added printer in CUPS to work for my printer at all, so I did the below:

If job is paused due to cups-browsed issue or otherwise doesn't work, try https://askubuntu.com/questions/1128164/no-suitable-destination-host-found-by-cups-browsed : remove cups-browsed sudo apt-get purge --autoremove cups-browsed then add printer manually via IPP in Add Printer in Administration tab of CUPS Web UI (it might automatically show up under Discovered Network Printers there using dnssd)

Once printer is working, go to Administration dropdown on printer page and Set as Server Default.

Try printing from Folk!

You can also test printing again with lpr ~/folk-printed-programs/SOMETHING.pdf (you have to print the PDF and not the PS for it to work, probably)

Projector-camera calibration

Position the camera. Make sure Folk is running (ssh in, cd ~/folk, ./folk.tcl start). Go to your Folk server's Web page http://whatever.local:4273/camera-frame to see a preview of what the camera sees. Reposition your camera to cover your table.
Go to the Folk calibration page at http://whatever.local:4273/calibrate and follow the instructions (print calibration board & run calibration process).

Connect a keyboard

Follow the instructions on this Folk wiki page to connect a new keyboard to your system.

Bluetooth keyboards

Install bluetoothctl. Follow the instructions in https://wiki.archlinux.org/title/bluetooth_keyboard to pair and trust and connect.

(FIXME: Write down the Bluetooth MAC address of your keyboard. We'll proceed as though it's "f4:73:35:93:7f:9d" (it's important that you turn it into lowercase).)

Potentially useful

Potentially useful for graphs: graphviz

Potentially useful: gdb, streamer, cec-utils, file, strace

Potentially useful: add folk-WHATEVER shortcut to your laptop ~/.ssh/config:

Host folk-WHATEVER
     HostName folk-WHATEVER.local
     User folk

Potentially useful: journalctl -f -u folk to see log of folk service

For audio: https://askubuntu.com/questions/1349221/which-packages-should-be-installed-to-have-sound-output-working-on-minimal-ubunt

HDMI No signal on Pi 4

Edit /boot/cmdline.txt raspberrypi/firmware#1647 (comment) (HDMI-A-1 or HDMI-A-2 depending on which port)

Ubuntu Server boots slowly

https://askubuntu.com/questions/1321443/very-long-startup-time-on-ubuntu-server-network-configuration (add optional: true to all netplan interfaces)

Troubleshooting

Why is my camera slow (why is tracking janky or laggy, why is camera time high)

Check that camera is plugged into a USB3 port

Turn off autoexposure and autofocus

for example, install v4l-utils and:

v4l2-ctl -c auto_exposure=1
v4l2-ctl -c focus_automatic_continuous=0
v4l2-ctl -c white_balance_automatic=0

Tcl troubleshooting

You can build Tcl with TCL_MEM_DEBUG. Download Tcl source code. (On Mac, do not go to the macosx/ subdir; go to the unix/ subdir.) Do ./configure --enable-symbols=all, do make, make install

License

Folk is available under the Apache 2.0 license. See the LICENSE file for more information.

Language reference

Folk is built around Tcl. We don't add any additional syntax or preprocessing to the basic Tcl language; all our 'language constructs' like When and Wish are really just plain Tcl functions that we've created. Therefore, it will eventually be useful for you to know basic Tcl syntax.

These are all implemented in main.tcl. For most things, you'll probably only need Wish, Claim, When, and maybe Hold.

Wish and Claim

Wish $this is labelled "Hello, world!"

Claim $this is cool
Claim Omar is cool

When

When /actor/ is cool {
   Wish $this is labelled "$actor seems pretty cool"
   Wish $actor is outlined red
}

The inside block (body) of the When gets executed for each claim that is being made that it matches. It will get reactively rerun whenever a new matching claim is introduced.

Any wishes/claims you make in the body will get automatically revoked if the claim that the When was matching is revoked. (so if Omar stops being cool, the downstream label Omar seems pretty cool will go away automatically)

The /actor/ in the When binds the variable actor to whatever is at that position in the statement.

It's like variables in Datalog, or parentheses in regular expressions.

Non-capturing

/someone/, /something/, /anyone/, /anything/ are special cases if you want a wildcard that does not bind (you don't care about the value, like non-capturing groups (?:) in regex), so you don't get access to $someone or $something inside the When.

Negation

/nobody/, /nothing/ invert the polarity of the match, so it'll run only when no statements exist that it would match.

This When will stop labelling if someone does Claim Omar is cool:

When /nobody/ is cool {
   Wish $this is labelled "nobody is cool"
}

`&` joins

You can match multiple patterns at once:

Claim Omar is cool
Claim Omar is a person with 2 legs
When /x/ is cool & /x/ is a person with /n/ legs {
   Wish $this is labelled "$x is a cool person with $n legs"
}

Notice that x here will have to be the same in both arms of the match.

You can join as many patterns as you want, separated by &.

If you want to break your When onto multiple lines, remember to terminate each line with a \ so you can continue onto the next line:

When /x/ is cool & \
    /x/ is a person with /n/ legs {
  Wish $this is labelled "$x is a cool person with $n legs"
}

Collecting matches

When the collected matches for [list /actor/ is cool] are /matches/ {
   Wish $this is labelled [join $matches "\n"]
}

This gets you an array of all matches for the pattern /actor/ is cool.

(We use the Tcl list function to construct a pattern as a first-class object. You can use & joins in that pattern as well.)

Hold

Experimental: Hold is used to register claims that will stick around until you do another Hold. You can use this to create the equivalent of 'variables', stateful statements.

Hold { Claim $this has a ball at x 100 y 100 }

When $this has a ball at x /x/ y /y/ {
    puts "ball at $x $y"
    After 10 milliseconds {
        Hold { Claim $this has a ball at x $x y [expr {$y+1}] }
        if {$y > 115} { set ::done true }
    }
}

Hold will overwrite all statements made by the previous Hold (scoped to the current $this).

Notice that you should scope your claim: it's $this has a ball, not there is a ball, so different programs with different values of $this will not stomp over each other. Not scoping your claims will bite you once you print your program and have both virtual & printed instances of your program running.

If you want multiple state atoms, you can also provide a key -- you can be like

Hold ball position {
  Claim $this has a ball at blahblah
}

and then future holds with that key, ball position, will overwrite this statement but not override different holds with different keys

You can overwrite another program's Hold with the on parameter, like Hold (on 852) { ... } (if the Hold is from page 852) or Hold (on virtual-programs/example.folk) { ... } (if the Hold is from the example.folk virtual program)

Every time

Experimental: Every time works almost like When, but it's used to hold when an 'event' happens without causing a reaction cascade.

You can't make Claims, Whens, or Wishes inside an Every time block. You can only Hold.

Example:

Hold { Claim $this has seen 0 boops }

Every time there is a boop & $this has seen /n/ boops {
  Hold { Claim $this has seen [expr {$n + 1}] boops }
}

If you had used When here, it wouldn't terminate, since the new $this has seen n+1 boops hold would cause the When to retrigger, resulting in a $this has seen n+2 boops hold, then another retrigger, and so on.

Every time, in contrast, will 'only react once' to the boop; nothing in its body will run again unless the boop goes away and an entirely new boop appears.

Animation

Getting time

Get the global clock time with:

When the clock time is /t/ {
  Wish $this is labelled $t
}

Use it in an animation:

When the clock time is /t/ {
  Wish $this draws a circle with offset [list [expr {sin($t) * 50}] 0]
}

You usually won't need these

When when

Lets you create statements only on demand, when someone is looking for that statement.

When /thing/ is cool {
    Wish $this is labelled "$thing is cool"
}
When when /personVar/ is cool /lambda/ with environment /e/ {
    Claim Folk is cool
}

On and Start

FIXME: General note: the On and Start blocks are used for weird non-reactive behavior. Need to fill this out more.

Start process

Start process A {
  while true {
    puts "Hello! Another second has passed"
    exec sleep 1
  }
}

On unmatch

You should not use When, Claim, or Wish directly inside an On unmatch block; those only make sense inside a normal reactive context.

set pid [exec python3]
On unmatch {
    kill $pid
}

Non-capturing

You can disable capturing of lexical context around a When with the (non-capturing) flag.

This is mostly to help runtime performance if a When is declared somewhere that has a lot of stuff in scope at declaration time.

set foo 3
When (non-capturing) /p/ is cool {
   Claim $p is awesome
   # can't access $foo from in here
}

Assert and Retract

General note: Assert and Retract are used for weird non-reactive behavior.

You should generally not use Assert and Retract inside a When block. Use Claim, Wish, and When instead.

Tcl for JavaScripters

JS:

let names = ["64", "GameCube", "Wii", "Switch"];
names = names.map(name => `Nintendo ${name}`);
console.log(names);

function add(a, b) { return a + b; }
const numbers = [1, 2];
console.log(add(...numbers));

Tcl:

set names [list 64 GameCube Wii Switch]
set names [lmap name $names {expr {"Nintendo $name"}}]
puts $names

proc add {a b} { expr {$a + $b} }
set numbers [list 1 2]
puts [add {*}$numbers]

Style guide

Tcl code vs. virtual programs vs. printed programs

In general, avoid adding new .tcl files to the Git repo. Pure Tcl libraries are an antipattern; we should only need them for the hard core of the system.

Most new code (both libraries and applications) should be virtual programs (which ilve as .folk files in the virtual-programs/ subfolder) or printed programs.

Folk

Use complete sentences when you word your claims and wishes.

Bad: Claim $this firstName Omar

Good: Claim $this has first name Omar
Scope using $this where appropriate to prevent weird global interactions

Bad: Claim the value is 3

Good: Claim $this has value 3

Style for joins across multiple lines -- use &\ and align on the first token after When:

When the fox is out &\
     the label is "Hello" &\
     everything seems good {
  ...
}

Tcl

fn

Use fn instead of proc to get a lexically captured command.

Error handling

Use try (and on error) in new code. Avoid using catch; it's older and easier to get wrong.

apply

Use apply instead of subst to construct lambdas/code blocks, except for one-liners (where you can use list)

Tcl datatypes

Create a namespace for your datatype that is an ensemble command with operations on that datatype.

(Examples: statement, c, region, point, image)

Call the constructor create, as in dict create and statement create.

Singletons

Capitalized namespace, like Statements.

FolkComputer/folk

Folk

Hardware

Linux tabletop installation using live USB

Manual Linux tabletop installation

How to control tabletop Folk from your laptop

General debugging

Printer support

Projector-camera calibration

Connect a keyboard

Bluetooth keyboards

Potentially useful

HDMI No signal on Pi 4

Ubuntu Server boots slowly

Troubleshooting

Why is my camera slow (why is tracking janky or laggy, why is camera time high)

Check that camera is plugged into a USB3 port

Turn off autoexposure and autofocus

Tcl troubleshooting

License

Language reference

Wish and Claim

When

Non-capturing

Negation

& joins

Collecting matches

Hold

Every time

Animation

Getting time

You usually won't need these

When when

On and Start

Start process

On unmatch

Non-capturing

Assert and Retract

Tcl for JavaScripters

Style guide

Tcl code vs. virtual programs vs. printed programs

Folk

Tcl

fn

Error handling

apply

Tcl datatypes

Singletons

`&` joins