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Comment by strogonoff | Hacker News Reader

TypeScript is limiting for describing schema in my experience. Try requiring an array of certain length, for example.

Also, it’s Turing-complete, so you are enabling future developers or users to shoot themselves in the foot and write something that does not halt already at configuration stage.

To me the perfect language for configuration seems to be Dhall, but it doesn’t seem to have gained any traction.

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Dhall is too unfamiliar for most developers, IMO. Developers don’t want to have to grok an entirely new syntax just for config. I’m personally surprised no one has added type annotations to Starlark yet.

The Rust implementation has it as an experimental extension (https://github.com/facebookexperimental/starlark-rust/blob/m...)

Oooh, very cool! I'll check it out and maybe port to Go.

Everything is unfamiliar, until one adopts it.

I didn't think it needed to be explained, but not all things are equally unfamiliar nor equally easily adopted.

Depending on what you're looking to do, you can use a tuple type to get an array of a certain length.

[number, number, number]

I meant length that depends on another type, not length known beforehand (e.g., if N widgets are defined somewhere, [up to] N elements can exist somewhere else, or configuration should not compile). Naturally, this had to involve generics (similar to [0], except I don’t recall why but the `length` property workaround didn’t work or didn’t provide sufficient type safety in my use case). Eventually, after reading workarounds in a related issue[1], I gave up. TypeScript’s type system is great for its intended use, but when applied to expressing schema constraints it quickly falls short and runtime code execution is required to validate a given structure with all the corresponding drawbacks.

[0] https://stackoverflow.com/q/56034226/247441

[1] https://github.com/microsoft/TypeScript/issues/26223

> not length known beforehand

Is that a feature of other languages?

Haven’t had much exposure to other statically typed languages recently, so can’t say off the top of my head. Intuitively it looks like something modern generics should allow easily though, doesn’t it?

As to Dhall, for example, I could validate such a constraint (and more) using a function I can be reasonably sure is safe and won’t halt (i.e. without all the drawbacks of TS and other general-purpose languages).

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