[treyd]

You can express a lot of concepts just through types in languages with richer type systems.

[shiandow]

Even without a rich type system you can express a lot of things just through naming.

You just can't enforce those assumptions.

[eyelidlessness]

You can enforce them (statically) by other means if you’re determined enough, eg by using lint rules which enforce type-like semantics which the type system itself doesn’t express.

[treyd]

This does rely on the language having a sophisticated-enough type system to be able to extract enough type information for the rules to work in the first place.