# different version of PosRational, more suitable for unit testing

class PosRational 

  # initialize is special; immediately called on result 
  # of PosRational.new
  def initialize(num,den=1) # default arguments
    if num < 0 || den <= 0
      raise "PosRational received an inappropriate argument"
    end
    @num = num # fields created when you assign to them
    @den = den
    reduce
  end

  def to_s  # override the standard to_s (to_string) method
    ans = @num.to_s
    if @den != 1 # everything true except false _and_ nil objects
      ans = ans + "/" + @den.to_s
    end
    return ans
  end

  # the documentation claims that the default version of inspect
  # uses to_s, but it doesn't seem to work that way ....
  def inspect
    to_s
  end

  def add r
    a = r.num # only works b/c of protected methods below
    b = r.den # only works b/c of protected methods below
    c = @num
    d = @den
    @num = (a * d) + (b * c)
    @den = b * d
    reduce
    self # convenient for stringing calls
  end

  # a functional addition, dynamic typing means now + works on rationals
  def + r
    ans = PosRational.new(@num,@den)
    ans.add(r)
    ans
  end
    
  attr_reader :num, :den
  protected :num, :den

private
  def gcd(x,y)
    if x == y
      x
    elsif x < y
      gcd(x,y-x)
    else
      gcd(y,x)
    end
  end

  def reduce 
    d = gcd(@num,@den)
    @num = @num / d
    @den = @den / d
  end
end