On: Open-sourcing Sorbet: a fast, powerful type checker for Ruby

[keithlfrost]

Clojure allows one to start with essentially untyped code, then add type declarations for efficiency and safety.

[kyllo → keithlfrost]

core.typed never really caught on though, what seems more popular is Schema which focuses on annotating and validating the structure of lists and maps: https://github.com/plumatic/schema

[Scarbutt → kyllo]

And Schema died in favor of Spec, which is still in flux.

[cutler → Scarbutt]

Spec isn't finalised but I wouldn't say it's in flux. It's 95% there.