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Hello World

This guide assumes you already installed Klar via Loom.

Create a project (optional)​

loom new exists mainly to generate a simple project tree and README. It is not required to run Klar.

loom new my-project
cd my-project

Loom will generate something like:

.
├── out/
├── README.md
└── src/
    └── main.kl

Your first Klar program​

Create src/main.kl:

@Use("java")
public void main(){
    println("Hello from Klar!");

    return null;
}

Notes:​

  • @Use("java") is required
  • public is required
  • void functions still return explicitly (return; also works, but return null; is currently recommended)

Run it​

kc run src/main.kl

Expected output:

Hello from Klar!

Program exited with code: 0

Where output goes​

Klar generates Java output in:

out/

You will usually see both:

  • *.java
  • *.class

If you get an error​

Klar fails fast and prints a structured diagnostic. Start with:

  • the diagnostic code ([K:Exxx])
  • the category (LEXICAL, SYNTAX, SEMANTIC, BACKEND, CLI)
  • the fix section

Further on, the Diagnostic Docs explain this in more detail.