symbol_stack.rb

class SymbolStack
  class Error < StandardError
  end

  def initialize(max_size = 10)
    @stack = []
    @max_size = max_size
  end

  def size
    @stack.size
  end

  def pop
    if @stack.size <= 0
      raise SymbolStack::Error, "stack is empty"
    else
      @stack.pop
    end
  end

  def push(elem)
    if !elem.kind_of? Symbol
      raise SymbolStack::Error, "argument should be symbol"
    elsif @stack.size >= @max_size
      raise SymbolStack::Error, "stack is full"
    else
      @stack.push(elem)
    end
  end
end