monads.rb

class ValidateSumOfMilliliters
  def call(form_object:)
    find_juice_by_id.(form_object.juice_id)
      .and_then { |juice| validate_sum_of_milliliters(juice: juice) }
      .or_else  { |error| fail_with_invalid_juice_id(error) }
  end

  private
  def fail_with_invalid_juice_id(error)
    interrupt(
      :invalid_attributes, 
      juice_id: "Juice with id #{error.juice_id} doesn't exist!"
    )
  end

  def find_juice_by_id
    Juices::Queries::ById.new(juice_repository)
  end

  # ...
end