The taste of ascent

type Stage = Kid | Teen | Adult;

# Get the stage based on age
fix stageOf = fn(age: Int): Stage =>
  if (age < 13) { Kid }
  else if (age < 20) { Teen }
  else { Adult };

# Generate a cheering message
fix cheer = fn(s: Stage): String => match s {
  Kid   -> "keep exploring",
  Teen  -> "the world is yours",
  Adult -> "welcome aboard",
};

program (name: String, age: Int) {
  mut sum = 0;
  for n in 1..(age + 1) {
    sum = sum + n;
  };
  fix stage = stageOf(age);

  """
  Hi ${name}! At ${age}, ${cheer(stage)}.
  Fun fact: 1 + 2 + ... + ${age} = ${sum}.
  """
}