stack.rb

# A very basic Stack implemented with an array  
# Makes use of the built in #pop and # push methods that exist for arrays.
class Stack
  def initialize
    @store = []
  end

  def push(x)
    @store.push x
  end

  def pop
    raise "Stack Underflow - The stack is empty" if self.empty?
    @store.pop
  end

  def peek
    @store.last
  end

  def empty?
    @store.empty?
  end
end