func activeCriteria(filter []string) string {
	expr := ""
	for i, name := range filter {
		if i > 0 {
			expr += " && "
		}
		expr += fmt.Sprintf("criteria[%q] != nil", name)
	}

	return expr
}
func activeCriteria(filter []string) string {
	expr := ""
	for i, name := range filter {
		if i > 0 {
			expr += " && "
		}
		expr += fmt.Sprintf("criteria[%q] != nil", name)
	}

	return expr
}
// Return an expression evaluating if a filter should be used (based on active
// criteria).