code: func serviceFunc(b *Brain, used, missing *dep.Set) func(...string) ([]*dep.HealthService, error) {
  	return func(s ...string) ([]*dep.HealthService, error) {
  		result := []*dep.HealthService{}
  
  		if len(s) == 0 || s[0] == "" {
  			return result, nil
  		}
  
  		d, err := dep.NewHealthServiceQuery(strings.Join(s, "|"))
  		if err != nil {
  			return nil, err
  		}
  
  		used.Add(d)
  
  		if value, ok := b.Recall(d); ok {
  			return value.([]*dep.HealthService), nil
  		}
  
  		missing.Add(d)
  
  		return result, nil
  	}
  }
docs: // serviceFunc returns or accumulates health service dependencies.