While

while checks its condition, runs its block if the condition is true, and goes round again:

var value = 10
while (value != 0) {
  println("${value}")
  value = value - 1
}

If the condition is false the first time, the block never runs.

A loop with one statement can use the colon form, with its statement on the same line:

var count = 0
while (count < 10): count = count + 1

Leaving early

break leaves the loop at once, and continue skips the rest of this time round and checks the condition again:

var count = 0
while (true) {
  count = count + 1
  if (count % 2 == 0): continue
  if (count > 9): break
  println("${count}")
}

Looping while a value is there

while can bind a value that may be absent, the way if can. The loop runs for as long as the value is there:

class Queue {
  var remaining = 3

  let next() : string? {
    if (remaining == 0) {
      return none
    }
    remaining = remaining - 1
    return "item"
  }
}

entrypoint main() {
  let queue = Queue()
  while (let item? = queue.next()) {
    println(item)
  }
}

do ... while, which runs its block before the first check, is not in V0 yet: write the loop with while.