Iteration

Forever Running Loop

This type of loop will run loop body forever unless you explicitly tell it to stop with break statement.

main {
  loop {
    body
  }
}

For example:

main {
  mut i := 0

  loop {
    if i < 10 {
      break
    }

    print(i++)
  }
}

Conditional Loop

This type of loop will run loop body while loop condition stays true.

main {
  loop condition {
    body
  }
}

For example:

main {
  mut i := 0

  loop i < 10 {
    print(i)
    i++
  }
}

C-style Loop

This type of loop is identical to the one that most programming languages support. It consists of initializer, condition, update and body.
Loop execution starts with initializer. You can define any variable here just like you would with variable declaration.
Next, loop execution continues with condition expression. If condition is true execution continues, otherwise it stops.
Next, loop execution continues with body, and then it executes update expression.
Finally, it continues execution with condition expression and repeats process while condition expression doesn’t return false.

main {
  loop initializer; condition; update {
    body
  }
}

NOTE:

Variables declared inside initializer are mutable by default. You don’t need to explicitly define them mutable with mut keyword.

For example:

main {
  loop i := 0; i < 10; i++ {
    print(i)
  }
}

Parenthesized/Multiline

Same as regular loop you can surround loop components with parenthesis if they are multiline.
This way it would be more self-describing to other people what is going on in this block of code.

main {
  loop (condition) {
    body
  }
}

main {
  loop (
    condition1 &&
    condition2 &&
    condition3
  ) {
    body
  }
}

main {
  loop (
    initializer;
    condition;
    update
  ) {
    body
  }
}