Calculator

calculator.rb

class Calculator

  def initialize(value="")
    @value ||= value
  end

  def method_missing(method, *args, &block)
    @value += tokenize(method.to_s)
    self
  end

  def tokenize(token)
    Calculator.numbers.merge(Calculator.operators)[token]
  end


  def ==(other_object)
    eval(@value) == other_object
  end

  def self.method_strings
    Calculator.numbers.map do |key, value|
      "def #{key}; Calculator.new('#{value}'); end"
    end
  end

  def self.numbers
    numbers = ["zero", "one", "two", "three", "four",
     "five", "six", "seven", "eight", "nine"]
    Hash[numbers.map.with_index { |value, index| [value, index.to_s] }]
  end

  def self.operators
    {"plus"        => "+",
     "minus"       => "-",
     "divided_by" => "/",
     "times"       => "*"}
  end
end

Calculator.method_strings.map {|x| eval(x)}

fail unless one.plus.two == 3
fail unless two.divided_by.four.plus.nine.times.three == 27
fail unless one.four.four.divided_by.one.two == 12

#The benefits of the above are that we can very easily add or modify operations.  For instance, we can easily do this

class Calculator
  def initialize(value="")
    @value ||= value
  end

  def method_missing(method, *args, &block)
    raise("bad token: #{method}") unless token = tokenize(method.to_s)
    @value += tokenize(method.to_s)
    self
  end

  def tokenize(token)
    Calculator.numbers.merge(Calculator.operators)[token]
  end


  def ==(other_object)
    eval(@value) == other_object
  end

  def self.method_strings
    Calculator.numbers.map do |key, value|
      "def #{key}; Calculator.new('#{value}'); end"
    end
  end

  def self.numbers
    numbers = ["zero", "one", "two", "three", "four",
     "five", "six", "seven", "eight", "nine", "ten",
     "eleven", "twelve", "thirteen", "fourteen", "fifteen",
     "sixteen", "seventeen", "eighteen", "nineteen", "twenty"]
    Hash[numbers.map.with_index { |value, index| [value, index.to_s] }]
  end

  def self.operators
    {"plus"            => "+",
     "minus"           => "-",
     "divided_by"      => "/",
     "over"            => "/",
     "times"           => "*",
     "open_paren"      => "(",
     "close_paren"     => ")",
     "to_the_power_of" => "**"}
  end
end

Calculator.method_strings.map {|x| eval(x)}

fail unless eighteen.to_the_power_of.two.times.open_paren.twelve.minus.four.close_paren.over.nine == 288