let hailstone = fn(n_) {
  var n = n_
  let steps = [n]
  loop {
    if n < 2 { break steps }
    n := (if n % 2 == 0 { n / 2 } else { n * 3 + 1 })
    steps.push(n)
  }
}

let twentySeven = hailstone(27)
print("The Hailstone sequence for 27 starts with:")
print(twentySeven.slice(0, 4))
print("and ends with:")
print(twentySeven.slice(-4))
print("and its length is:")
print(twentySeven.len())

print("Checking sequences up to 100,000")
var longest = 0
var longestLen = 0
for i in range(100000) {
  let len = hailstone(i).len()
  if len > longestLen {
    longest := i
    longestLen := len
  }
  if i % 10000 == 0 {print(i)}
}
print("The longest sequence under 100,000 is for:")
print(longest)
print("and has length:")
print(longestLen)