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Joo is a programming language created to run on machines with extremely low resources like microcontrollers.

I had this idea while playing around with the Arduios and Retruino, the arduios has a lot of potential on it's own but i just wanted more. And this project is the result of that.

I've developed the first functional version of it as a weekend hack a while ago, so there's quite a lot to do as it has a lot of potential and the compiler and virtual machine code could be a lot better.

Since the code wasn't that good i wanted to refactore it before publishing, the new code is in the refactoring branch, but there's just so much to do that i decided to publish it as it is, because as i already said it has a lot of potential and if i publish it maybe a community will grow and it will be developed faster and in ways i can't even dream about right now!

Join our discord!

Using the Joo SDK

To start download the SDK at builds/JooSDK.jar, then create a new file called Test.joo in the same folder as the SDK file and paste the code below.

include StandartLibrary

int helloWorld = 10

function Start
	call Print helloWorld
endFunction

Then execute it using the joo command.

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The commands supported are

  • joo <file> If the specified file is a .cjoo file, executes the code. If the file is a .joo file compiles it then executes it.

  • joo -compile <file> Compiles the .joo file, and generates a .cjoo file in the same folder.

  • joo -create <file> Creates a .joo file at the specified path with the Joo template code.

  • joo -help Shows the Joo SDK help message.

Programming the Arduino UNO with Joo

Arduios allows you to use a sketch in different use cases, without having to upload a new one every time. But joo is on a whole new level, you just need to upload the ArduinoJooVM once, then you can upload any joo binary using the serial port of the arduino and the vm will execute it.

You're probably thinking, how does it work? The Arduino UNO only has 2KB of ram. Well, that's where the magic happens, if you wan't to understant how it works, read The Joo byte code language.

To start upload the ArduinoJooVM sketch at builds/ArduinoJooVM/ArduinoJooVM.ino. After uploading open the serial monitor and copy the byte code in the Test.cjoo file created in Using the Joo SDK and send it.

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If you have a sd card module you can use it by changing the BYTE_CODE_SOURCE variable of the VM in the sketch, copying the Test.cjoo file to the sd card and renaming it to bytecode.txt. The VM will load and execute the code on Arduino start.

Note that the Execute native function only works with a sd card.

Adding syntax highlight to Notepad++

To make it easier to develop joo code i've created a custom syntax highlight for Notepad++.

  1. Download the src/main/resources/SyntaxHighlight/Notepadpp/SyntaxHighlight.xml file.

  2. In Notepad++ go to Language>User defined language>Define your language...>Import and import the file.

  3. Select Joo as the file's languages.

The Joo programming language

Is a clean, fast, static typed, general purpose language.

Code files are saved as .joo files that get compiled to .cjoo files.

Comments look like this

# this is a single line comment

##
this is a 
multi-line comment
##

Right now 4 data types are supported int, fixed (fixed point 8.8 bytes), bool and char. I'm planning to add string someday. I implemented fixed point instead of floating point for performance reasons.

int myInt # it's not necessary to assign a value
int myIntWithValue = 50

fixed myFixed = 12.34
bool myBool = true/false 1/0
char myChar = 'A'

A constant is a value that can't be changed, it doesn't have a type, the compiler just replaces it's name with it's value at compile time.

constant MY_CONSTANT = 10

int myInt = MY_CONSTANT

The include keyword allows to add library code from .jlib files in the same directory or subdirectories using their name. The compiler just adds the code of the file to the end of the code in the current file.

include MyLibrary
include Directory/MyLibrary

Every code, except for variable and constant declarations and includes, needs to be inside a function, at the moment the first function in the code is the one the virtual machine calls to start executing. Functions can have up to 6 parameters.

int myInt
bool myBool

function Start
	call MyFunction myInt myBool # executes MyFunction with the specified arguments
	repeatFunction # restarts the execution of the function
endFunction

function MyFunction int _myInt bool _myBool
	# write code here
endFunction

All 4 supported data types can also be used as a array. The max length of array is 54.

int:10 myArray # declares a array with size 10

function Start
	myArray:5 = 25 # assigns the value 25 to the 5th index of the array.
endFunction

Conditions are also supported with the if, elseIf and else keywords.

int firstValue = 10
int secondValue = 5

function Start
	if firstValue == secondValue
		# code goes here
	elseIf firstValue == 8
		# code goes here
	else
		# code goes here
	endIf
endFunction

Only binary operators are supported, means you need 2 variables, the same variable in both sides of the operator or a value after the operator.

myInt + 5
myInt1 + myInt2
myInt1 -= myInt1

The operators implemented in the standart library are

operator <= int|fixed 				# smaller-equals comparator
operator >= int|fixed 				# bigger-equals comparator
operator < int|fixed 				# smaller comparator
operator > int|fixed 				# bigger comparator
operator == int|fixed|bool|char 		# equals comparator
operator != int|fixed|bool|char 		# not equals comparator
operator = int|fixed|bool|char 			# assign operator 
operator =+ int|fixed|bool 			# positive assign operator
operator =- int|fixed|bool 			# negative assign operator
operator =! int|fixed|bool 			# invert assign operator
operator + int|fixed 				# add operator
operator - int|fixed 				# subtract operator
operator * int|fixed 				# multiply operator
operator / int|fixed 				# divide operator
operator % int 					# modulus operator
operator & int 					# bitwise AND operator
operator ^ int 					# bitwise XOR operator
operator | int 					# bitwise OR operator
operator ~ int 					# bitwise NOT operator
operator << int 				# bit shift left operator
operator >> int 				# bit shift right operator

It's possible to declare custom operators and native functions. Native functions are functions that are implemented in the virtual machine, so it allows you to call native code from joo as well as change the value of the variables passed as arguments. At the moment if you have custom operators or native functions you have to modify the vm and recompile it so you can execute your stuff.

# The supported types are separated with a |
operator == int|fixed|bool|char
operator += int|fixed

native HelloWorld int|fixed bool int|char
# native functions are called like other functions call HelloWorld myInt myBool myInt

The joo programming laguage has a standart library, even if very bare bones right now, it has common used operators and native functions that are already implemented in the default build of the virtual machine.

You can include the standart library using

include StandartLibrary
The Execute native function

Since the Arduino UNO only has 2kb of RAM, the amount of byte code that can be loaded at once is very limited. To handle this, the standart library has the Execute native function. It allows to execute other joo programs at runtime, by loading them from the sd card.

To use it you have to put all programs you want to execute at runtime in the same folder as your main program. When compiling, the compiler will scan for the .joo files in the folder and include them in the .cjoo file. You can basically create multiple microprograms that will build one program, and each of these can have the max byte code size the VM can handle. After that you can switch the executing program with the Execute native function.

So lets say you have a directory with multiple microprograms

MyJooProject
>MyJooMainProgram.joo
>MyJooMicroprogram.joo
>MyJooLibrary.jlib
>MyJooMainProgram.cjoo

When you compile it with

joo -compile MyJooMainProgram.joo

All files will be included in the MyJooMainProgram.cjoo and you can execute it with

joo MyJooMainProgram.cjoo

In code, you can execute the MyJooMicroprogram with

call Execute MyJooMicroprogram

And re-execute the MyJooMainProgram with

call Execute MyJooMainProgram
Known limitations

Most of the limitations are a result of the extremely efficient byte code.

  • 64 variables + functions
  • 6 parameters/function
  • 54 max array size
  • Function call arguments must be variables.
  • Number type variable declaration doesn't support negative values.

Well, you know, i'm lazy and don't exactly know how to explain things, specialy since i've never created a programming language before and there's so much to explain, so take a look at the test code at src/test/resources as well as the compiler and virtual machine code. It will help you get a better understanding of the language and how the magic happens.

The Joo byte code language

The joo byte code language uses single characters/bytes in the range 0 - 127 to represent the compiled code executed by the virtual machine.

* 0 - 0		end of file
* 1 - 65  	variable and function names
* 66 - 72  	parameter names
* 73 - 127 	array indices
* 91 - 127 	numbers, keywords and types
* 1 - 127 	operators, native functions

So let's say you have this code

int myInt
bool myBool

function Start
	myInt = 10
	myBool = true
	call MyFunction myBool myInt
endFunction

function MyFunction bool _testBool int _testInt
	_testBool = false
	_testInt = 5
endFunction

Since in byte code the names of the variables and functions a.k.a components are represented in as 1 number in the range 1 - 65 the byte code the names are

  • myInt = 1
  • myBool = 2
  • Start = 3
  • MyFunction = 4

The MyFunction parameter names are

  • _testBool = 66
  • _testInt = 67

so the byte code of the code above looks like

int 1
bool 2

function 3
	1 = 10
	2 = true
	call 4 2 1
endFunction

function 4
	66 = false
	67 = 5
endFunction

Of course the keywords are also replaced by their single byte representation. The MyFunction parameters don't need to be declared in the byte code since the type and parameter count checks happen at compile time.

Pretty smart isn't it? *guy taping head meme*

The Joo virtual machine

The language can be easily extended with operator and native function libraries. But their functionality needs to be implemented in the virtual machine.

Custom operators

To create a custom operator, first of all you need to declare it in joo code

operator += int|fixed

And then you need to implement it in the virtual machine

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This will only work if you include the standart library as you're continuing the operator names of it, otherwise you need to write

#define OPERATOR_MY_OPERATOR 0 + OPERATORS_START

Then just reupload the sketch or recompile the virtual machine and the operator can already be used in code.

include StandartLibrary

operator += int|fixed

int myInt = 10

function Start
	myInt += 5
endFunction

Custom native functions

It's the same process as for the operator, declare it in joo code

native MyFunction int char

And the implement it in the virtual machine

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Then just reupload the sketch or recompile the virtual machine and the native function can already be used in code.

include StandartLibrary

native MyFunction int char

int myInt
char myChar = 'A'

function Start
	call MyFunction myInt myChar
endFunction