def traceback_array
      trace = []
      traceback do |i,j,flags|
        trace << [i,j,flags]
      end
      trace
    end
def traceback_array
      trace = []
      traceback do |i,j,flags|
        trace << [i,j,flags]
      end
      trace
    end
traceback
 Like traceback, but returns an array of the traceback instead of
 yielding blocks.