#
# $Id: lazy.rb,v 1.5 2003/02/23 18:19:57 fukumoto Exp $
#

require 'thread'

def Lazy(*param, &p)
  Lazy.new(*param, &p)
end

class Lazy
  def initialize(*params, &block)
    super()
    @mutex = Mutex.new
    @done = false
    @value = nil
    @block = block
    @params = params
  end

  def __eval__
    @mutex.synchronize do
      if not @done
	@value = @block.yield(*@params)
	@done = true
	@block = nil		# to garbage collect
	@params = nil
      end
    end
  end

  def inspect
    if @done
      # sprintf("#<Lazy:0x%x @value=%s>", self.id, @value.inspect)
      @value.inspect
    else
      sprintf("#<Lazy:0x%x>", self.id)
    end
  end

  def to_a
    if not @done then __eval__ end
    @value.to_a
  end

  def to_s
    if not @done then __eval__ end
    @value.to_s
  end

  def ==(other)
    if not @done then __eval__ end
    @value == other
  end

  def =~(other)
    if not @done then __eval__ end
    @value =~ other
  end

  def ===(other)
    if not @done then __eval__ end
    @value === other
  end

  def method_missing(name, *args, &p)
    if not @done then __eval__ end
    @value.__send__ name, *args, &p
  end

end # end of class Lazy