code: func TransformComprehensions(x interface{}, f func(interface{}) (Value, error)) (interface{}, error) {
  	t := &GenericTransformer{func(x interface{}) (interface{}, error) {
  		switch x := x.(type) {
  		case *ArrayComprehension:
  			return f(x)
  		case *SetComprehension:
  			return f(x)
  		case *ObjectComprehension:
  			return f(x)
  		}
  		return x, nil
  	}}
  	return Transform(t, x)
  }
docs: // TransformComprehensions calls the functio nf on all comprehensions under x.