Your first cobra4 program

Save this as hello.c4:

fn main() {
    name = "world"
    log("hello", to=name)

    # `each` is a list comprehension when an expression
    squares = each n in [1, 2, 3, 4] { n * n }
    log("squares", values=squares)
}

main()

Run it:

c4 run hello.c4

You should see:

2026-05-07T17:00 level=info msg=hello to=world
2026-05-07T17:00 level=info msg=squares values=[1, 4, 9, 16]

What c4 run actually did

c4 run hello.c4 is a one-shot pipeline:

1. Parse hello.c4 with the Lark grammar → AST.
2. Resolve scopes; warn on undefined names / shadowing.
3. Type-check (gradual; advisory).
4. Codegen → Python source.
5. Execute the generated Python with the cobra4 runtime imported.

To see the Python that gets executed:

c4 build hello.c4 -o hello.py
cat hello.py

You can also open the same project in Cobra4 Studio:

c4 studio

Studio shows the generated Python beside the Cobra4 source and uses the compiler source map to highlight which generated lines came from each source line.

Other useful commands

c4 studio                # browser Studio: edit, run, inspect generated Python
c4 fmt   hello.c4         # canonical re-format from AST
c4 check hello.c4         # lint + type warnings, no execution
c4 doctor                # local install + project health checks
c4 repl                   # multi-line REPL with completion + history
c4 doc   hello.c4         # extract docstrings to markdown
c4 test                   # discover and run tests/test_*.c4
c4 serve hello.c4         # run as a daemon (every / on event / serve)
c4 lsp                    # language server (used by IDE extensions)