Functional Eye for the Ruby Guy

And then he makes it worse by throwing those out, defining `multiple_of`, and using method_missing to make `multiple_of_{3,5}` still work. A big part of reading unfamiliar code is looking up the implementation of things, and this is just making it more laborious and confusing.

If this was correctly using lazy enumerators, it wouldn't require a range to be passed in, and you would take values from the resulting lazily evaluated enumerators until you found one >= 1000. All the laziness does here is prevent the select from being evaluated until the sum is called.

I don't have 2.0 installed, so this probably has bugs/errors/etc, but I believe this is what he was going for.

  module TakeUntil
    refine Enumerator::Lazy do
      def take_until(&b)
        next_obj = take(1).first
        if yield(next_obj)
          []
        else
          [next_obj] + take_until(&b)
        end
      end 
    end
  end

  class FunctionalRuby
    using TakeUntil
    def sum_of_multiples_under(max)
      (1..99999999).lazy.select { |x| (x % 3 == 0) || (x % 5 == 0) }.take_until { |x| x > 1000 }.sum
    end
  end

  FunctionalRuby.new.sum_of_multiples_under(1000)