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

Other useful commands

c4 fmt   hello.c4         # canonical re-format from AST
c4 check hello.c4         # lint + type warnings, no execution
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)