stream.go
func Contents(filters ...Filter) ([]string, error) {
	var result []string
	err := ForEach(Sequence(filters...), func(s string) {
		result = append(result, s)
	})
	if err != nil {
		result = nil // Discard results on error
	}
	return result, err
}
func Contents(filters ...Filter) ([]string, error) {
	var result []string
	err := ForEach(Sequence(filters...), func(s string) {
		result = append(result, s)
	})
	if err != nil {
		result = nil // Discard results on error
	}
	return result, err
}
// Contents returns a slice that contains all items that are
// the output of filters.