Johann is a programming platform for arm64-apple-darwin (aka Apple Silicon, with macOS). You don't want to use it. You don't even want to look at the source. When a bored coder has a martini (or several...) and decides to single-handedly reinvent much of the past ~60 years of computer science from scratch, nothing good results.
The nominal goal is to get 2025's Advent of Code stars using only Johann, via its self-hosted compiler.
Clone, compile, and link a test program as below. You'll need the command-line developer/Xcode tools installed.
git clone git@github.com:barneyb/johann.git
cd johann
echo 'pub fn main() { puts("Hello, world!"); }' | ./bin/jnc > hello.s
gcc hello.s ./lib/jstdlib.o
./a.out
This will print exactly what you'd expect1:
Hello, world!
If you're intrigued (or mortified), barneyb.github.io/johann/ has additional info for human consumption. The sources are the definitive resource, of course.
1 If you start any computer programming project with something more complicated than printing 'Hello, world!', you've already introduced your first defect, even if you can't see it yet.