class RRPN

# File lib/rrpn.rb, line 12
def self.calc(queue)
  stack = []

  until queue.empty?
    v = queue.shift
    stack << v

    if %i(+ - * / ** << >> % & ^ |).include?(stack.last)
      receiver, arg, op = stack.pop(3).map { |e| e.instance_of?(String) ? eval(e) : e }
      stack << receiver.send(op, arg)
    elsif %i(~ -@ +@).include?(stack.last)
      receiver, op = stack.pop(2).map { |e| e.instance_of?(String) ? eval(e) : e }
      stack << receiver.send(op)
    end
  end

  stack.pop
end

# File lib/rrpn.rb, line 31
def initialize(formula)
  @formula = formula
  stree = Ripper.sexp(@formula)
  @queue = parse(stree[1..-1]).flatten
end

# File lib/rrpn.rb, line 66
def calc
  RRPN.calc(queue.dup)
end

# File lib/rrpn.rb, line 37
def parse(tree)
  queue = []

  case tree[0]
    when :paren
      queue << parse(tree[1..-1])
    when :binary
      return [parse(tree[1]), parse(tree[3]), tree[2]]
    when :unary
      return [parse(tree[2]), tree[1]]
    when :@int
      return tree[1].to_i
    when :@float
      return tree[1].to_f
    when :@rational
      return tree[1]
    when :@imaginary
      return tree[1]
    else
      if tree[0].instance_of?(Array)
        queue << parse(tree[0])
      else
        raise "Parse failed. '#{@formula}' - #{tree.inspect}"
      end
  end

  queue
end

# File lib/rrpn.rb, line 70
def to_s
  queue.join(' ')
end