code: func Uniq() Filter {
  	return FilterFunc(func(arg Arg) error {
  		first := true
  		last := ""
  		for s := range arg.In {
  			if first || last != s {
  				arg.Out <- s
  			}
  			last = s
  			first = false
  		}
  		return nil
  	})
  }
docs: // Uniq squashes adjacent identical items in arg.In into a single output.