Hello, world!

Let's run our first Vine program!

// vine/examples/hello_world.vi

pub fn main(&io: &IO) {
  io.println("Hello, world!");
}

We can run this with:

vine run vine/examples/hello_world.vi

You should see something like the following:

Hello, world!

Interactions
  Total                  297
  Annihilate             159
  Commute                  0
  Copy                    17
  Erase                   34
  Expand                  46
  Call                    27
  Branch                  14

Memory
  Heap                   480 B
  Allocated            6_016 B
  Freed                6_016 B

Performance
  Time                     0 ms
  Speed            8_054_237 IPS

At the top, notice that it successfully printed Hello, world!.

At the bottom, you'll also see several statistics printed out. You don't need to worry about them for now. If you want to disable them, you can use --no-stats.

Let's break down what just happened.

• fn main: declares a function, named main
  • pub: makes it public
  • (&io: &IO): it takes a single parameter:
    • &IO: of type &IO
    • &io: to be dereferenced and bound to the variable io
  • { ... }: in the function body
    • io.println: uses the println method on IO
    • ("Hello, world!"): calls it with the string Hello, world!

We'll go into this in more detail in future chapters.

Every Vine program must contain a pub fn main(&io: &IO) { ... } ("a public function main that takes a reference to IO").