def flatten_sequence(list)
      foldl(list.compact) { |r, e|        # and then merge flat elements
        merge_fold(r, e)
      }
    end
def flatten_sequence(list)
      foldl(list.compact) { |r, e|        # and then merge flat elements
        merge_fold(r, e)
      }
    end
Flatten results from a sequence of parslets.

 @api private