# ==============================================================================
# 
# 	RubyFORTH -- Copyright (C) 2007-8, Marc Simpson (GPL). 
# 
#	Stack module
# 
# ==============================================================================

class Stack
  def initialize(size)
    @contents = Array.new(size)
    @offset = -1
  end
  def nth(n)
    @contents[@offset - n]
  end
  def tos
    if @offset < 0
      puts "Error: stack underflow"
      false
    else 
      @contents[@offset]
    end
  end
  def push(n)
    @offset += 1
    @contents[@offset] = n
  end
  def pop
    if @offset < 0
      puts "Error: stack underflow"
      @offset = -1
      throw("toplevel")
      return
    end
    @offset -= 1
    @contents[@offset + 1]
  end
  def _contents
    0.upto(@offset) do |i| 
      elt = @contents[i]
      elt = "'#{elt}'" if elt.class == String
      print "#{elt} " 
    end
    print "\n"
  end
  def depth
    @offset + 1
  end 
  def contents
    print "<#{@offset + 1}> "
    self._contents
  end
  def swap
    x = self.pop ; y = self.pop
    self.push(x) ; self.push(y)
  end
  def reset
    @offset = -1 
  end 
  def each
    0.upto(@offset) { |i| yield @contents[i] }
  end
end