infer polymorphism

[KotlinIsland]

def f(a):  # def f[T](a: T) -> T
    return a

def find(data: list, predicate: "(...) -> ..."):  # find[T](data: list[T], predicate: (T) -> T) -> T
    for item in data:
        if predicate(item):
            return item
     raise ValueError

probs many more cases, and maybe we can use ... in the type position to mean "this must be inferable"