Your first program

Start with one directory and one source file. A simple Noodle program does not need a manifest or a module declaration.

mkdir hello

Create hello/hello.nl:

func greeting(name : String) -> String do
  "Hello, " ++ name ++ "!"
end

func main() -> Unit do
  Console.println(greeting("Noodle"));
end

The greeting function declares the types at its boundary. Its final expression is the returned String. The main function is the program entry point and returns Unit, the type used when no meaningful value is returned.

Check and run it

Ask Noodle to check every source file in the directory:

noodle check hello

Then select hello.nl as the program entry file:

noodle run hello/hello.nl

The program prints:

Hello, Noodle!

Add a test

Tests can live beside the code they exercise. Update hello/hello.nl so the complete file is:

func greeting(name : String) -> String do
  "Hello, " ++ name ++ "!"
end

func main() -> Unit do
  Console.println(greeting("Noodle"));
end

test "builds a greeting" do
  Testing.assert_equal(greeting("Noodle"), "Hello, Noodle!")!;
end

Run all tests in the directory:

noodle test hello

The postfix ! propagates an assertion failure to the test runner. For now, read it as “this test fails if the assertion fails.” Its general behavior is explained in Error handling, while the Testing API is documented under Output, debugging, and tests.

Next, learn how these commands fit into the everyday workflow.