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Hello, Raven

The REPL​

On its own, the raven command launches a REPL. It makes a nifty little calculator:

$ raven
> 2+2
4
> Complex(1, 2) / 2
0.5 + 1.0im
> factorial(big(50))
big(30414093201713378043612608166064768844377641568960512000000000000)

Running a script​

Like Ruby or Python, there's no main function; code at the top level just runs, line by line. So this one-liner is a complete program:

hello.rv
println("Cacaw, World!")
$ raven hello.rv
Cacaw, World!

Building a binary​

Under the hood, raven hello.rv compiles your code to WebAssembly and immediately runs it. You can split those steps up:

$ raven build hello.rv
$ raven hello.wasm
Cacaw, World!

The .wasm file is a self-contained binary that any WebAssembly runtime can execute. You can name the output with -o, so the above is the same as raven build hello.rv -o hello.wasm.

Building for JavaScript​

Raven can also emit a JS file, ready for Node or the browser:

$ raven build --js hello.rv
$ ./hello.js
Cacaw, World!

Adding --embed packs the wasm inside the JS, giving you a single self-contained script:

$ raven build --js --embed hello.rv -o hello
$ ./hello
Cacaw, World!

See Embedding Raven in JS/TS for how to call Raven functions from JavaScript, and the CLI reference for all the build options.

Something meatier​

Here's a program that actually computes something:

fib.rv
fn fib(n) { fib(n-1) + fib(n-2) }
fn fib(1) { 1 }
fn fib(0) { 0 }

fn fibSequence(n) {
  xs = []
  for i = range(1, n) {
    append(&xs, fib(i))
  }
  return xs
}

show fibSequence(10)
$ raven fib.rv
fibSequence(10) = [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

A few things to notice: fib is defined three times, and calls pick the right definition by matching on the arguments; append(&xs, ...) uses the swap operator to update a variable; and show is a handy macro that prints an expression along with its value.

From here, work through the Language Guide – it starts from the basics and covers everything the language can do today.