list_compare.rb

def <=>(other)
  head.match do |lm|
    lm.none do
      other.head.match do |rm|
        rm.some { -1 }
        rm.none { 0 }
      end
    end
    lm.some do |left_head|
      other.head.match do |rm|
        rm.none { +1 }
        rm.some do |right_head|
          (left_head <=> right_head).yield_self do |comparison|
            if comparison == 0
              tail <=> other.tail
            else
              comparison
            end
          end
        end
      end
    end
  end
end

list_compare_while.rb

def <=>(other)
  left = self
  right = other
  until left.empty? || right.empty?
    comparison = left.head! <=> right.head!
    if comparison == 0
      left = left.tail
      right = right.tail
    else
      return comparison
    end
  end
  case [left.empty?, right.empty?]
  when [true, true] then 0
  when [true, false] then -1
  when [false, true] then +1
  end
end