scores.rb

def calculate_score(term)
  if score can be calculated
    Score.new(value)
  else
    NoScore
  end
end

def save_score(term, score)
  if score.available?
    value = score.value
    save the value
  else
    save a NULL
  end
end

scores.sml

val calculateScore : string -> real option
val saveScore : (string, real option) -> unit

fun calculateScore term = if something then SOME score else NONE
fun saveScore (term, SOME score) = save that score!
  | saveScore (term, NONE) = don't save it, or save nil