Math Object Model Example

model.rb

#!/usr/bin/env ruby
# Chris Sivanich 2015

class Node
  def initialize
  end

  def to_s
  end

  def evaluate
  end
end

class MinusNode < Node
  def initialize(left, right)
    @left = left
    @right = right
  end

  def to_s
    return "(#{@left} - #{@right})"
  end

  def evaluate
    return @left.evaluate() - @right.evaluate()
  end
end

class IntNode < Node
  def initialize(value)
    @value = value
  end

  def to_s
    return @value
  end

  #WARN only int
  def evaluate
    return @value
  end
end

class MultNode < Node
  def initialize(left, right)
    @left = left
    @right = right
  end

  def to_s
    return "(#{@left} * #{@right})"
  end

  def evaluate
    return @left.evaluate() * @right.evaluate()
  end
end

class PlusNode < Node
  def initialize(left, right)
    @left = left
    @right = right
  end

  def to_s
    return "(#{@left} + #{@right})"
  end

  def evaluate
    return @left.evaluate() + @right.evaluate()
  end
end

class IntNode < Node
  def initialize(value)
    @value = value
  end

  def to_s
    return @value.to_s
  end

  def evaluate
    return @value
  end
end


# Start main script here
#

# Completely necessary at some point, but clearer to declare ahead of time
one = IntNode.new(1)
two = IntNode.new(2)
three = IntNode.new(3)

# More pretty objects
one_plus_two = PlusNode.new(one, two)
three_minus_one = MinusNode.new(three, one)
five_times_five = MultNode.new(IntNode.new(5), IntNode.new(5))

expr = PlusNode.new(PlusNode.new(one_plus_two, three_minus_one), five_times_five)

# (((1 + 2) + (3 - 1)) + (5 * 5))
puts expr.to_s

# 30
puts expr.evaluate