I'm a big believer in 'Perlis languages', where you learn a language for new perspectives and approaches rather than needing it for a specific domain.
The tricky bit is: when can you say you've acquired those new perspectives?
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Delighted to see that TOML has released a new version! TOML is overall a great standard but I understand they had limited people with the power to cut a new release.
https://github.com/toml-lang/toml/releases/tag/1.1.0
The niche of short, environment-specific scripts, and the consequences for programming language design choices: https://brrt-to-the-future.blogspot.com/2021/03/why-bother-with-scripting.html
I've heard of 'blub languages', where you don't realise that other languages have better abstractions until you've experienced them.
I think the same thing happens with individual features. I've seen several C++ folks miss variadic generics in Rust, but I've not written enough C++ to feel it.