code: func (s *Schema) Subscribe(ctx context.Context, queryString string, operationName string, variables map[string]interface{}) (<-chan interface{}, error) {
  	if s.res == nil {
  		return nil, errors.New("schema created without resolver, can not subscribe")
  	}
  	return s.subscribe(ctx, queryString, operationName, variables, s.res), nil
  }
docs: // Subscribe returns a response channel for the given subscription with the schema's
  // resolver. It returns an error if the schema was created without a resolver.
  // If the context gets cancelled, the response channel will be closed and no
  // further resolvers will be called. The context error will be returned as soon
  // as possible (not immediately).