Tests aren’t enough: Case study after adding type hints to urllib3

Post by munificent » Mon, Oct 18, 2021, 10:10 PM UTC

slaymaker1907 wrote: post #113

tetha wrote: post #97

Earlier quoted context omitted.

Hm, growing somewhat experienced, I find myself adapating an old quote more and more: Sufficiently advanced static typing is indistinguishable from dynamic typing. Now, I know, it's not true. It's entirely possible to build weird things in python that are provably impossible to typecheck statically. But modern language servers and their type inference capabilities in rust, terraform, or even straight up python are ve…

Please write a type for the following function: def compose(start, *args): def helper(x): for func in reversed(args): x = func(x) return start(x) return helper There is no mainstream typed language which can write a fully general type for the vararg compose function. TypeScript is probably the one that comes closest, but last I checked it still was unable to write a sufficiently powerful array type. You can write a t…

Post by albrewer » Mon, Oct 18, 2021, 10:12 PM UTC

slaymaker1907 wrote: post #113

tetha wrote: post #97

Earlier quoted context omitted.

Hm, growing somewhat experienced, I find myself adapating an old quote more and more: Sufficiently advanced static typing is indistinguishable from dynamic typing. Now, I know, it's not true. It's entirely possible to build weird things in python that are provably impossible to typecheck statically. But modern language servers and their type inference capabilities in rust, terraform, or even straight up python are ve…

Please write a type for the following function: def compose(start, *args): def helper(x): for func in reversed(args): x = func(x) return start(x) return helper There is no mainstream typed language which can write a fully general type for the vararg compose function. TypeScript is probably the one that comes closest, but last I checked it still was unable to write a sufficiently powerful array type. You can write a t…

  from typing import Callable, Any

  def compose(start: Callable[[Any], Any], *args: Callable[[Any], Any] -> Callable[[Any], Any]:
    def helper(x: Any) -> Any:
      for func in reversed(args):
        x = func(x)
      return start(x)
    return helper

Post by jayd16 » Mon, Oct 18, 2021, 10:14 PM UTC

jfabre wrote: post #64

malfist wrote: post #32

Earlier quoted context omitted.

How in the world does type checking lower the ceiling on excellence?

Tbh I'm conflating multiple things, I've heard a lot of good things about Haskell. But in C# for example, if the system was not designed with dependency injection and everything being an interface it's very hard to build a test harness since you can't mock anything. Which means everything has to be tested manually. (I haven't done any C# in a long time, maybe it's not the case anymore) So you have to create an interf…

Post by slaymaker1907 » Mon, Oct 18, 2021, 10:18 PM UTC

albrewer wrote: post #133

slaymaker1907 wrote: post #113

Earlier quoted context omitted.

Please write a type for the following function: def compose(start, *args): def helper(x): for func in reversed(args): x = func(x) return start(x) return helper There is no mainstream typed language which can write a fully general type for the vararg compose function. TypeScript is probably the one that comes closest, but last I checked it still was unable to write a sufficiently powerful array type. You can write a t…

I took a stab at it, there's not enough information to figure out anything more specific: from typing import Callable, Any def compose(start: Callable[[Any], Any], *args: Callable[[Any], Any] -> Callable[[Any], Any]: def helper(x: Any) -> Any: for func in reversed(args): x = func(x) return start(x) return helper

Post by slaymaker1907 » Mon, Oct 18, 2021, 10:21 PM UTC

monocasa wrote: post #125

slaymaker1907 wrote: post #113

Earlier quoted context omitted.

Please write a type for the following function: def compose(start, *args): def helper(x): for func in reversed(args): x = func(x) return start(x) return helper There is no mainstream typed language which can write a fully general type for the vararg compose function. TypeScript is probably the one that comes closest, but last I checked it still was unable to write a sufficiently powerful array type. You can write a t…

I think you can in rust as long as args is a slice. Rust doesn't have varargs except for c interop. A slice or Vec of function pointers is the idiomatic way to do the same thing. Something like: fn compose (start: Box X>, args: Vec T>>) -> Fn(T) -> X { move |x: X| { let mut x = x; for func in args.iter(). reversed() { x = func(x); } start(x) } }