# File lib/sfl.rb, line 81
    def redirection_ast(v, what_for = :out)
      case v
      when Integer
        raise NotImplementedError, "Redirection to integer FD not yet implemented"
      when :close
        nil
      when :in, :out, :err
        REDIRECTION_MAPPING[v]
      when String # filename
        [File, :open, v, (what_for == :in ? 'r' : 'w')]
      when Array # filename with option
        [File, :open, v[0], v[1]]
      when IO
        v
      end
    end