Dynamic properties in Typed Racket

[hanwenguo]

Consider the following Python Code:

class Node:
    def __init__(self) -> None:
        self.wins: int = 0
        # self.losses: int = 0
        self.parent: None | Node = None

    def score1(self) -> int:
        n = 0
        if self.parent is not None:
            n += self.parent.wins
        if self.parent is not None:
            n += self.parent.losses
        return n

    @property
    def losses(self):
        self.wins = 0
        self.parent = None
        return 0

    def score2(self) -> int:
        n = 0
        if self.parent is not None:
            n += self.losses
            n += self.parent.wins # no type error !?
        return n

n = Node()
m = Node()
n.parent = m
print(n.score2())

It suggests a unsound hole in the type system of Pyright and mypy (both of them suggest no type error as of 2024-10-22) due to dynamic properties performing operations on other properties. Does Racket has similar issues?

[bennn]

note: Static Python succeeds, it does report a type error in the score2 method

[bennn]

I can't think of a nice way to do this in TR.

A class contract might work: impersonate the class & use get-field in the body & field access should be able to run arbitrary code. But impersonators are detectable (with eq?).
https://docs.racket-lang.org/reference/Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29

class-field-accessor and class-field-mutator might work somehow, but I don't see how to call those during a field access.
https://docs.racket-lang.org/reference/ivaraccess.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class-field-accessor%29%29

For now, let's say this is not possible in TR. (It's definitely not standard.)

[bennn]

Matthew can't think of a way either. Good!