extract_source.rb

def extract_source(parent)
  $source ||= File.readlines(__FILE__)
  if parent.first_lineno == parent.last_lineno
    src = $source[parent.first_lineno][parent.first_column..parent.last_column]
  else
    src = ' ' * parent.first_column + $source[parent.first_lineno][parent.first_column..]
    ((parent.first_lineno + 1)...(parent.last_lineno)).each do |lineno|
      src << $source[lineno]
    end
    src << $source[parent.last_lineno][0..parent.last_column]
  end

  src
end