Hello World

This page walks you through writing, running, and understanding your first Tova program.

Your First Program

Create a file called hello.tova:

name = "World"
print("Hello, {name}!")

Run it:

tova run hello.tova

Output:

Hello, World!

That is all it takes. Let us break down what happened.

What Just Happened

Immutable by default. The line name = "World" creates an immutable binding. Once assigned, name cannot be reassigned. If you need a mutable variable, use var:

var counter = 0
counter += 1       // OK -- counter is mutable

String interpolation. Curly braces inside a string evaluate expressions inline. Any valid expression works:

print("2 + 3 = {2 + 3}")       // 2 + 3 = 5
print("upper: {upper(name)}")  // upper: WORLD

Implicit returns. The last expression in a block is its return value. No return keyword is needed (though you can use one for early returns).

Adding a Function

Extend hello.tova with a function:

name = "World"
print("Hello, {name}!")

fn add(a, b) {
  a + b
}

result = add(1, 2)
print("1 + 2 = {result}")

Run it again:

tova run hello.tova

Output:

Hello, World!
1 + 2 = 3

Functions are declared with fn. The body is a block delimited by curly braces, and the last expression is returned implicitly. There are no semicolons in Tova.

Try "Hello World" in Playground

Lambdas

Anonymous functions use the same fn keyword without a name:

double = fn(x) x * 2

print("double 5 = {double(5)}")   // double 5 = 10

For multi-line lambdas, use braces:

transform = fn(x) {
  y = x * 2
  y + 1
}

Using the REPL

For quick experimentation, start the interactive REPL:

tova repl

You will see a prompt where you can type Tova expressions and see results immediately:

tova> 1 + 2
3
tova> name = "Tova"
"Tova"
tova> print("Hello from {name}!")
Hello from Tova!
tova> fn square(x) { x * x }
tova> square(7)
49

The REPL supports multi-line input and has the full standard library available. Type :help to see available commands, or :quit to exit.

A Slightly Bigger Example

Here is a program that puts several features together:

fn fizzbuzz(n) {
  for i in range(1, n + 1) {
    match [i % 3, i % 5] {
      [0, 0] => print("FizzBuzz")
      [0, _] => print("Fizz")
      [_, 0] => print("Buzz")
      _      => print("{i}")
    }
  }
}

fizzbuzz(20)

This shows for loops, range, pattern matching on arrays, and wildcard patterns -- all concepts covered in the Tour of Tova.

Try "FizzBuzz" in Playground

Next Steps

• Tour of Tova -- a fast-paced walkthrough of every major language feature
• Variables -- deep dive into immutability, mutability, and destructuring
• Functions -- default parameters, rest parameters, and more