[fulafel]

Another option besides types is using a schema library. You can do more things, like define custom validation rules over eg several fields, publish the schema as data (eg at an API endpint, openapi or json schema etc), reuse it in another language (depending on schema system), version it explicitly, and machine generate it if it comes from some external spec (like a db schema).

Also great for property testing / fuzzing. And other fun meta datamodel stuff like eg inferring schema from example data.

In general programming language type systems are pretty weak in comparison because they're not very programmable. (In most languages, for most people, etc .. there are fancy level type systems approaching formal proof toolkits but they're hard to use)