Fluent Calculator

calc_v1.rb

class Calc
  DIGITS = [:zero, :one, :two, :three, :four, :five, :six, :seven, :eight, :nine]
  
  def method_missing method
    if DIGITS.include?(method)
      DIGITS.index(method)
    else
      super
    end
  end
end

describe Calc do
  @calc = Calc.new
  describe 'digits' do
    it 'returns its numeric value' do
      Test.assert_equals(@calc.one, 1)
      Test.assert_equals(@calc.four, 4)
      Test.assert_equals(@calc.nine, 9)
    end
  end
end

calc_v2.rb

class Calc
  DIGITS = [:zero, :one, :two, :three, :four, :five, :six, :seven, :eight, :nine]
  
  DIGITS.each do |digit|
    define_method(digit) do
      DIGITS.index(digit)
    end
  end

end

describe Calc do
  @calc = Calc.new
  describe 'digits' do
    it 'returns its numeric value' do
      Test.assert_equals(@calc.one, 1)
      Test.assert_equals(@calc.four, 4)
      Test.assert_equals(@calc.nine, 9)
    end
  end
end

calc_v3.rb

class Calc
  DIGITS = [:zero, :one, :two, :three, :four, :five, :six, :seven, :eight, :nine]

  attr_accessor :operand, :operator
  
  DIGITS.each do |digit|
    define_method(digit) do
      numeric_value = DIGITS.index(digit)
      if @operand and @operator
        @operand.send(@operator, numeric_value)
      else
        @operand = numeric_value
        self
      end
    end
  end
  
end

describe Calc do

  describe 'digits' do
    it 'returns itself' do
      Test.assert_equals(Calc.new.one.class, Calc)
    end
    it 'returns its numeric value' do
      Test.assert_equals(Calc.new.one.operand, 1)
      Test.assert_equals(Calc.new.four.operand, 4)
      Test.assert_equals(Calc.new.nine.operand, 9)
    end
  end
  
end

calc_v4.rb

class Calc
  DIGITS = [:zero, :one, :two, :three, :four, :five, :six, :seven, :eight, :nine]
  
  DIGITS.each do |digit|
    define_method(digit) do
      numeric_value = DIGITS.index(digit)
      if @operand
        @operand.send(@operator, numeric_value)
      else
        @operand = numeric_value
        self
      end
    end
  end
  
  attr_accessor :operand, :operator
  
  def plus
    @operator = :+
    self
  end
  
  def minus
    @operator = :-
    self
  end
  
  def times
    @operator = :*
    self
  end
  
  def divided_by
    @operator = :/
    self
  end
  
end

describe Calc do

  describe 'digits' do
    it 'returns itself' do
      Test.assert_equals(Calc.new.one.class, Calc)
    end
    it 'returns its numeric value' do
      Test.assert_equals(Calc.new.one.operand, 1)
      Test.assert_equals(Calc.new.four.operand, 4)
      Test.assert_equals(Calc.new.nine.operand, 9)
    end
  end
  
  describe 'operators' do
    it 'returns itself' do
      Test.assert_equals(Calc.new.one.plus.class, Calc)
    end
    it 'sets the operator' do
      Test.assert_equals(Calc.new.one.plus.operator, :+)
    end
  end
  
end

calc_v5.rb

class Calc
  DIGITS = [:zero, :one, :two, :three, :four, :five, :six, :seven, :eight, :nine]
  
  DIGITS.each do |digit|
    define_method(digit) do
      numeric_value = DIGITS.index(digit)
      if @operand
        @operand.send(@operator, numeric_value)
      else
        @operand = numeric_value
        self
      end
    end
  end
  
  attr_accessor :operand, :operator
  
  def plus
    @operator = :+
    self
  end
  
  def minus
    @operator = :-
    self
  end
  
  def times
    @operator = :*
    self
  end
  
  def divided_by
    @operator = :/
    self
  end
  
end

describe Calc do

  describe 'digits' do
    it 'returns itself' do
      Test.assert_equals(Calc.new.one.class, Calc)
    end
    it 'returns its numeric value' do
      Test.assert_equals(Calc.new.one.operand, 1)
      Test.assert_equals(Calc.new.four.operand, 4)
      Test.assert_equals(Calc.new.nine.operand, 9)
    end
  end
  
  describe 'operators' do
    it 'returns itself' do
      Test.assert_equals(Calc.new.one.plus.class, Calc)
    end
    it 'sets the operator' do
      Test.assert_equals(Calc.new.one.plus.operator, :+)
    end
  end
  
  describe 'operations' do
    it 'performs additions' do
      Test.assert_equals(Calc.new.one.plus.three, 4)
    end
    it 'performs substraction' do
      Test.assert_equals(Calc.new.nine.minus.four, 5)
    end
    it 'performs multiplication' do
      Test.assert_equals(Calc.new.two.times.six, 12)
    end
    it 'performs divisions' do
      Test.assert_equals(Calc.new.nine.divided_by.three, 3)
    end
  end
  
end

calc_v6.rb

class Calc
  DIGITS = [:zero, :one, :two, :three, :four, :five, :six, :seven, :eight, :nine]
  OPERATORS = {plus: :+, minus: :-, times: :*, divided_by: :/}
  
  attr_accessor :operand, :operator

  DIGITS.each do |method_name|
    define_method(method_name) do
      numeric_value = DIGITS.index(method_name)
      if @operand
        @operand.send(@operator, numeric_value)
      else
        @operand = numeric_value
        self
      end
    end
  end

  OPERATORS.each do |method_name, operator|
    define_method(method_name) do
      @operator = operator
      self
    end
  end
  
end

describe Calc do

  describe 'digits' do
    it 'returns itself' do
      Test.assert_equals(Calc.new.one.class, Calc)
    end
    it 'returns its numeric value' do
      Test.assert_equals(Calc.new.one.operand, 1)
      Test.assert_equals(Calc.new.four.operand, 4)
      Test.assert_equals(Calc.new.nine.operand, 9)
    end
  end
  
  describe 'operators' do
    it 'returns itself' do
      Test.assert_equals(Calc.new.one.plus.class, Calc)
    end
    it 'sets the operator' do
      Test.assert_equals(Calc.new.one.plus.operator, :+)
    end
  end
  
  describe 'operations' do
    it 'performs additions' do
      Test.assert_equals(Calc.new.one.plus.three, 4)
    end
    it 'performs substraction' do
      Test.assert_equals(Calc.new.nine.minus.four, 5)
    end
    it 'performs multiplication' do
      Test.assert_equals(Calc.new.two.times.six, 12)
    end
    it 'performs divisions' do
      Test.assert_equals(Calc.new.nine.divided_by.three, 3)
    end
  end
  
end