?- A = point{x:1, y:2}.put(x, 3).
A = point{x:3, y:2}.

This predicate can also be accessed by using the functional notation, in which case Key can also be a *path* of keys. For example:

?- Dict = _{}.put(a/b, c).
Dict = _6096{a:_6200{b:c}}.