public type Row {
  id: Id
  count: Int
}

public type Problem {
  error Rejected(message: Text)
}

public adjust(value: Int) (answer: Int) {
  answer = value + 1
}

public make(value: Int) (row: Row) {
  row = Row { id = dever.id.fromText("雪")
    count = value }
}

public positive(value: Int >= 0) (answer: Int) {
  answer = value
}
public positive(value: Int < 0) (answer: Int) {
  fail(Problem.Rejected("negative"))
}