def consume(n)
      position = self.pos
      slice_str = @str.scan(@re_cache[n])
      slice = Parslet::Slice.new(
        position, 
        slice_str,
        @line_cache)

      return slice
    end
def consume(n)
      position = self.pos
      slice_str = @str.scan(@re_cache[n])
      slice = Parslet::Slice.new(
        position, 
        slice_str,
        @line_cache)

      return slice
    end
Consumes n characters from the input, returning them as a slice of the
 input.