lib/formula.rb
def arrayorize(value)
      case value
      when nil    then return []
      when String then value.to_s.split
      when Symbol then value.to_s.split
      else value
      end
    end
def arrayorize(value)
      case value
      when nil    then return []
      when String then value.to_s.split
      when Symbol then value.to_s.split
      else value
      end
    end
Create an array from a string, a symbol, or an undefined value. The default is to return
 the value and assume it has already is valid.