Hello, world!

Let’s run our first Vine program!

// hello_world.vi

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

We can run this with:

vine run hello_world.vi

You should see something like the following:

Hello, world!

Interactions
  Total                  341
  Annihilate             180
  Commute                  0
  Copy                    23
  Erase                   47
  Expand                  36
  Call                    41
  Branch                  14

Memory
  Heap                   640 B
  Allocated            7_216 B
  Freed                7_216 B

Performance
  Time                     0 ms
  Speed           10_740_157 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”).