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Jou programming language

Jou is a programming language that looks like Python but behaves like C. For example:

import "stdlib/io.jou"

def main() -> int:
    printf("Hello World\n")

    # Print numbers 0 to 9
    for i = 0; i < 10; i++:
        printf("%d\n", i)

    return 0

See the examples and tests directories for more example programs or read the Jou tutorial.

For now, Jou is great for writing small programs that don't have a lot of dependencies. For example, I solved all problems of Advent of Code 2023 in Jou, and I'm currently working on Advent of Code 2024. See examples/aoc2023 and examples/aoc2024 for the code.

I think Jou will be useful for two kinds of people:

  • People who find C programming fun but like Python's syntax
  • Python programmers who want to try programming at a lower level (maybe to eventually learn C or Rust)

See also AI's thoughts on Jou.

Design goals and non-goals

Jou eliminates some surprising things in C. For example:

  • In C, char may or may not be signed, depending on your OS, but Jou's byte data type is always unsigned.
  • In C, negative % positive is negative or zero, which means that array[i % array_len] doesn't wrap around as expected. In Jou, negative % positive is positive or zero.
  • Jou doesn't have strict aliasing. This means that in Jou, memory is just bytes, and you can't get UB by interpreting the same bytes in different ways, like you can in C.
  • Jou has Windows support that doesn't suck. You simply download and extract a zip, and add it to PATH. (See instructions below.)

I will try my best to keep Jou simple, and not turn it into yet another big language that doesn't feel like C, such as C++, Zig, Rust, and many others. For example, the recommended way to print things will be C's printf() function, as explained in the Jou tutorial. This also means that I reject many feature requests.

Jou is not intended to be memory safe, because it would make Jou more difficult to use. See Jou's UB documentation for more discussion, including thoughts on Rust.

Setup

These instructions are for using Jou. The instructions for developing Jou are in CONTRIBUTING.md.

Linux
  1. Install the dependencies: 
    $ sudo apt install git llvm-14-dev clang-14 make
    Let me know if you use a distro that doesn't have apt, and you need help with this step.
  2. Download and compile Jou. 
    $ git clone https://github.com/Akuli/jou
$ cd jou
$ make
  3. Run the hello world program to make sure that Jou works: 
    $ ./jou examples/hello.jou
Hello World
    You can now run other Jou programs in the same way.
  4. (Optional) If you want to run Jou programs with simply jou filename instead of something like ./jou filename or /full/path/to/jou filename, you can add the jou directory to your PATH. To do so, edit ~/.bashrc (or whatever other file you have instead, e.g. ~/.zshrc): 
    $ nano ~/.bashrc
    Add the following line to the end: 
    export PATH="$PATH:/home/yourname/jou/"
    Replace /home/yourname/jou/ with the path to the folder (not the executable file) where you downloaded Jou. Note that the ~ character does not work here, so you need to use a full path (or $HOME) instead.

These LLVM/clang versions are supported:

  • LLVM 11 with clang 11
  • LLVM 13 with clang 13
  • LLVM 14 with clang 14

By default, the make command picks the latest available version. You can also specify the version manually by setting the LLVM_CONFIG variable:

$ sudo apt install llvm-11-dev clang-11
$ make clean    # Delete files that were compiled with previous LLVM version
$ LLVM_CONFIG=llvm-config-11 make
MacOS

MacOS support is new. Please create an issue if something doesn't work.

  1. Install Git, make and LLVM 13. If you do software development on MacOS, you probably already have Git and make, because they come with Xcode Command Line Tools. You can use brew to install LLVM 13: 
    $ brew install llvm@13
  2. Download and compile Jou. 
    $ git clone https://github.com/Akuli/jou
$ cd jou
$ make
  3. Run the hello world program to make sure that Jou works: 
    $ ./jou examples/hello.jou
Hello World
    You can now run other Jou programs in the same way.
  4. (Optional) If you want to run Jou programs with simply jou filename instead of something like ./jou filename or /full/path/to/jou filename, you can add the jou directory to your PATH. To do so, edit ~/.bashrc (or whatever other file you have instead, e.g. ~/.zshrc): 
    $ nano ~/.bashrc
    Add the following line to the end: 
    export PATH="$PATH:/Users/yourname/jou/"
    Replace /Users/yourname/jou/ with the path to the folder (not the executable file) where you downloaded Jou. Note that the ~ character does not work here, so you need to use a full path (or $HOME) instead.
NetBSD Support for NetBSD is still experimental. Please report bugs and shortcomings.
  1. Install the dependencies: 
    # pkgin install bash clang git gmake libLLVM
    Optionally diffutils can be installed for coloured diff outputs.
  2. Download and compile Jou. 
    $ git clone https://github.com/Akuli/jou
$ cd jou
$ gmake
  3. Run the hello world program to make sure that Jou works: 
    $ ./jou examples/hello.jou
Hello World
    You can now run other Jou programs in the same way.
  4. (Optional) If you want to run Jou programs with simply jou filename instead of something like ./jou filename or /full/path/to/jou filename, you can add the jou directory to your PATH. Refer to the manual page of your login shell for exact syntax.

NB: Using Clang and LLVM libraries built as a part of the base system is not currently supported.

64-bit Windows
  1. Go to releases on GitHub. It's in the sidebar at right.
  2. Choose a release (latest is probably good) and download a .zip file whose name starts with jou_windows_64bit_.
  3. Extract the zip file somewhere on your computer.
  4. You should now have a folder that contains jou.exe, lots of .dll files, and subfolders named stdlib and mingw64. Add this folder to PATH. If you don't know how to add a folder to PATH, you can e.g. search "windows add to path" on youtube.
  5. Write Jou code into a file and run jou filename.jou on a command prompt. Try the hello world program, for example.

Updating to the latest version of Jou

Run jou --update.

Editor support

Tell your editor to syntax-highlight .jou files as if they were Python files. You may want to copy some other Python settings too, such as how to handle indentations and comments.

If your editor uses a langserver for Python, make sure it doesn't use the same langserver for Jou. For example, vscode uses the Pylance language server, and you need to disable it for .jou files; otherwise you get lots of warnings whenever you edit Jou code that would be invalid as Python code.

For example, I use the following configuration with the Porcupine editor:

[Jou]
filename_patterns = ["*.jou"]
pygments_lexer = "pygments.lexers.Python3Lexer"
syntax_highlighter = "pygments"
comment_prefix = '#'
autoindent_regexes = {dedent = 'return( .+)?|break|pass|continue', indent = '.*:'}

To apply this configuration, copy/paste it to end of Porcupine's filetypes.toml (menubar at top --> Settings --> Config Files --> Edit filetypes.toml).

How does the compiler work?

See CONTRIBUTING.md.