[BWStearns]

> I consider [having a big benefit at 100% vs an 80/20 rule] a characteristic of type systems in general; a type system that you can rely on is vastly more useful than a type system you can almost rely on, and it doesn’t take much “almost” to greatly diminish the utility of a given type system.

This! This is why I don't particularly care for gradual typing in languages like Python. It's a lot of extra overhead but you still can't really rely on it for much. Typescript types are just barely over the hump in terms of being "always" enough reliable to really lean on it.

[dimal]

I agree with the 100% rule. The problem with Typescript is how many teams allow “any”. They’ll say, “We’re using TypeScript! The autocomplete is great!” And on the surface, it feels safe. You get some compiler errors when you make a breaking change. But the any’s run through the codebase like holes in Swiss cheese, and you never know when you’ll hit one, until you’ve caused a bug in production. And then they try to deal with it by writing more tests. Having 100% type coverage is far more important.

[klabb3]

In my rather small code base I’ve been quite happy with ”unknown” instead of any. It makes me use it less because of the extra checks, and catches the occasional bug, while still having an escape hatch in cases of extensive type wrangling.

The other approach, having an absolutist view of types, can be very constraining and complex even for relatively simple domain problems. Rust for instance is imo in diminishing returns territory. Enums? Everyone loves them, uses them daily and even write their own out of joy. OTOH, it took years of debate to get GATs implemented (is it now? I haven’t checked), and not because people like and need them, but because they are a necessary technicality to do fundamental things (especially with async).

[WorldMaker]

Typescript's --strict is sometimes a very different ballgame from default. I appreciate why in a brownfield you start with the default, but I don't understand how any project starts greenfield work without strict in 2025. (But also I've fought to get brownfield projects to --strict as fast as possible. Explicit `any` at least is code searchable with the most basic grep skills and gives you a TODO burndown chart for after the fastest conversion to --strict.)

Typescript's --strict still isn't technically Sound, in the functional programming sense, but that gets back to the pragmatism mentioned in the article of trying to get that 80/20 benefit of enough FP purity to reap as many benefits without insisting on the investment to get 100% purity. (Arguably why Typescript beat Flow in the marketplace.)

[sevensor]

> you still can't really rely on it for much

And yet, type annotations in Python are a tremendous improvement and they catch a lot of bugs before they ever appear. Even if I could rely on the type system for nothing it would still catch the bugs that it catches. In fact, there are places where I rely on the type system because I know it does a good job: pure functions on immutable data. And this leads to a secondary benefit: because the type checker is so good at finding errors in pure functions on immutable data, you end up pushing more of your code into those functions.

[d0mine]

It may be the exact opposite. You can't express (at least you shouldn't try to avoid Turing tarpit-like issues) all the desired constraints for your problem domain using just the type system (you need a readable general purpose programming language for that).

If you think your type system is both readable and powerful then why would you need yet another programming language? (Haskell comes to mind as an example of such language--don't know how true it is). The opposite (runtime language used at compile time) may also be successful eg Zig.

Gradual typing in Python provides the best of both worlds: things that are easy to express as types you express as types. On the other hand, you don't need to bend over backwards and refactor half your code just to satisfy your compiler (Rust comes to mind). You can choose the trade off suitable for your project and be dynamic where it is beneficial. Different projects may require a different boundary. There is no size fits all.

P.S. As I understand it, the article itself is about "pragmatism beats purity."

[aabhay]

On the other hand, if you think of a programming language as a specialized tool then you choose the tool for the job and don’t reach for your swiss army knife to chop down a tree.

The problem with gradually typed languages is that there are few such trees that should be chopped by their blunt blades. At least Rust is the best for a number of things instead of mediocre at all of them.

One counterpoint to this is local self exploratory programming. For that a swiss army knife is ideal, but in those cases who cares about functional programming or abstractions?