3 ms·

Imagine ... 1. a -> b :: Function(a)[b] (a, k1=t1, k2=t2) -> b :: Function(a, k1=t1, k2=t2)[b] 2. JSON = RecTypeVar('JSON', lambda Self: Union[None, bool,

• throwaway894345 6y ago
  In fairness I find (1) to even less readable than the existing Callable syntax, but yeah, it would be cool if Python could express callables with kwargs and recursive types.
• duckerude 6y ago
  > 2. JSON = RecTypeVar('JSON', lambda Self: Union[None, bool, int, float, str, List[Self], Dict[str, Self]]) You don't actually need this workaround—the problem is typechecker support, not syntax. You can use strings for forward definitions, like this: JSON = Union[str, int, None, bool, List["JSON"], Dict[str, "JSON"]] What happens next depends on your typechecker. Mypy says this: error: Cannot resolve name "JSON" (possible cyclic definition) Pytype says this: Recursive type annotations not supported yet But Pyre accepts it and correctly uses it for typechecking.