When operating on rows one can add, remove, and update fields. A good syntax for this can be tricky to come up with.
I'm thinking that for object extension I can use an operator like @, ++, {+}, ɸ, or Ͼ.
Another good option would be to have an alternative syntax within { }'s, like {x + y} to concatenate two objects or {x + {...}} to extend an object with more fields. The interpretation of the curly brackets would thus depend on the operator inside.