DeferrableBlock.rb

class DeferrableBlock

  attr_reader :deferred
  attr_reader :binding

  def initialize(block, binding=nil)
    @code = block
    @binding = binding || Kernel.binding
    @deferred = false
  end

  def self._load(block)
    binding = Kernel.binding
    code, variables = Marshal.load(block)

    variables.each do |var,val|
      next if var == 'block' || var == 'binding'  
      binding.eval("#{var}=Marshal.load(#{val.inspect})")
    end

    new(code,binding)
  end

  def _dump( depth )
    @binding.eval('variables = Hash.new')
    @binding.eval('local_variables.each { |sym| variables[sym.to_s]=Marshal.dump(eval(sym.to_s)) if sym!=:variables}')
    a = [ @code, @binding.eval('variables') ]
    s = Marshal.dump(a)
  end

  def step_eval(code, start_line=0)
    @deferred = false
    code.each_index do |i|
      next if i < start_line 
      puts ">>"+@code[i] 
      if @code[i]=="pause"
        @binding.eval("line = #{i+1}")
        @deferred=true
        break
      end
      @binding.eval @code[i]
    end

  end
  
  def call(params={}) 
    params.each {|param,val| @binding.eval("#{param} = #{val}") }
    step_eval @code
  end

  def continue
    step_eval(@code, @binding.eval('line'))
  end

  def freeze(name)
    File.open(name, "w") { |file| Marshal.dump(self, file) }
  end   

  def self.unfreeze(name)
    File.open(name) { |file| Marshal.load(file) }
  end
  
  def self.resume(name)
    block = self.unfreeze(name)
    block.continue
  end

end

code = Array.new([
                    "a = 1",
                    "b = 2",
                    "puts b",
                    "pause",
                    "b += c",
                    "puts b"
                 ]);

block = DeferrableBlock.new(code)
block.call( {'c'=>5 } )
block.freeze("/tmp/block")

puts "And now for something different"

DeferrableBlock.resume("/tmp/block")