Stripe has released a static gradual type system for Ruby! https://sorbet.org/blog/2019/06/20/open-sourcing-sorbet
Perhaps the moral here is to worry about a building a great runtime, and only worry about the type system if your language gains traction?
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UUIDs are acceptable for APIs, but I really like Stripe's 'hungarian notation' approach. It's obvious what 'cus_123abc' is (a customer!).
"One of your test API keys has been filled into the examples, so you can test out any example right away." Stripe, I'm impressed.