Say I have a function that takes a value and a arbitrary number of functions, let's call the function for chain_call. Without types a simple naive implementation would be: def chain_call(input_value, *args): for function in args: input_value = function(input_value) return input_value As you imagine, input_value could be anything really but it's always the same as the first and only required argument of the first Callable in *args: List[Callable]. From here and forward the Callable´s first and only required argument is the same type as the previous items return-type. So far I've managed to define a quite generic type but it's too loose. def chain_call(input_value: Any, *args: List[Callable[Any], Any]) -> Any: ... What I'd really like is something like T = TypeVar('T') def chain_call(input_value: T, *args: List[Callable[T, ...], tr]) -> tr: ... Where T for Callable n+1 is tr of Callable n and the final return-type is tr of Callable n_max. I'm not sure how to express this with the type system and would love any guidance. Continue reading...
