Fluent Calculator

fluent_calc.rb

#Complex yet elegant
class Calc
  { zero: 0, one: 1, two: 2, three: 3, four: 4, five: 5, six: 6, seven: 7, eight: 8, nine: 9 }.each do |m, n|
    define_method("#{m}") { @proc ? @proc.call(n) : (@number ||= n ; self ) }
  end
  
  { plus: :+, minus: :-, times: :*, divided_by: :/ }.each do |m, o|
    define_method("#{m}") { @proc ||= lambda { |a| @number.send(o, a) }; self } 
  end
end

class Calc
  attr_accessor :first, :second, :operator
  %w(zero one two three four five six seven eight nine).each_with_index do |method,value|
    define_method(method) do
      if first.nil?
        self.first = value
        self
      else
        self.second = eval("#{self.first} #{operator} #{value}")
      end
    end
  end

  def plus
    @operator = "+"
    self
  end

  def times
    @operator = "*"
    self
  end
end

describe Calc do
  describe "#zero" do
    it 'returns corresponding digit 0' do
      calc = Calc.new
      expect(calc.zero).to be_a Calc
    end
  end

  describe "#one" do
    it 'returns corresponding digit 1' do
      calc = Calc.new
      expect(calc.one).to be_a Calc
    end
  end

  describe "#two" do
    it 'returns corresponding digit 2' do
      calc = Calc.new
      expect(calc.two).to be_a Calc
    end
  end

  describe "#times" do
    it 'returns 2 for 2 times one' do
      calc = Calc.new
      expect(calc.two.times.one).to eq(2)
    end
  end

  describe "#plus" do 
    it 'returns sum of two numbers' do
      calc = Calc.new
      expect(calc.one.plus.two).to eq(3)
    end

    it 'returns a sum of 3 for 2 plus 1' do
      calc = Calc.new
      expect(calc.two.plus.one).to eq(3)
    end

    it 'returns a sum of 4 for two plus two' do
      calc = Calc.new
      expect(calc.two.plus.two).to eq(4)
    end
  end
end