Dump code to be eval'd in a file so as to get a useful traceback if/when it fails.

eval_in_file.rb

def eval_in_file(source, options={})
  suffix = options[:suffix] || Time.now.strftime("%s%N")
  path = options[:path] || "/tmp/"
  result = nil
  filename = "#{path}eval-#{suffix}.rb"
  file = File.new(filename, 'w+')
  file.write(source)
  file.rewind

  begin
    result = binding.eval(file.read, file.path)
  rescue
    raise
  else
    File.unlink(filename)
  ensure
    file.close
  end
  result

end