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Comment by pansa2 | Hacker News Reader

> It seems every scripting language does duck/dynamic typing (as far as I can tell this applies to Koto).

It looks like Koto supports type hints - not sure if these are checked at compile-time, run-time, or both.

> I don’t understand why… inferred typing is nearly as easy to use while being more robust.

Is it (nearly as easy to use)? Every static type system seems to have special cases and exceptions which are avoided by dynamic typing. I'd love to find one that's actually simple.

Also, it's definitely not nearly as easy to implement - which is important for a language being designed and built by a small team and targeting a lightweight runtime.

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> Also, it's definitely not nearly as easy to implement

I think this is the real reason why there are so many dynamic language implementations. If you want to implement a dynamic language, you just slap a type tag on your runtime objects and boom, your "type system" is done.

Dynamic languages get a lot of expressiveness "for free", whereas having a really expressive static type system requires a lot of work. It's not that hard to get a type system on the level of C, but if the language is interpreted, it's still going to be pretty slow.

I do think there can be benefits to having typing in a scripting language (and not a bolted-on type system like typescript or mypy). It's much easier to work with an FFI if the type system of the scripting language maps closely to the implementation language. It also does make it much easier to optimize the language down the line, if that becomes a priority. Making a fully dynamic language efficient is very, very difficult.

> not sure if these are checked at compile-time, run-time, or both

It looks like Koto only checks types at run-time. That means its type annotations are essentially shorthand for something like Python's `if not isinstance(...): raise TypeError`.

Yes that's right, they're checked at runtime (with the option to disable the checks if the performance cost is a concern) and failed checks simply throw exceptions.

The hints aren't used for other purposes at compile time yet, but they could enable some warnings.

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