Refinement typing (the TS way) is relatively common in type systems that sit on top of dynamic languages because basically they have no choice. Binding to a new

Refinement typing (the TS way) is relatively common in type systems that sit on top of dynamic languages because basically they have no choice. Binding to a new variable, however, is a heck of a lot easier to analyse so tends to be done in languages that don’t need to implement refinement typing. A couple of interesting exceptions: explicit interfaces make it impractical in C#, and there’s a project called liquid Haskell that adds refinement typing on top of an already strong type system.