The answer I’ve seen is “just pass structs of functions around”, which is just one step more explicit than the implicit version we’re all use to, but honestly I kinda like it to free ourselves of all the ceremony around generics.

Gleam has first class functions, so it has dynamic dispatch.

Both of type classes and interfaces desugar to high order functions, so anything you write with them can be written with first class functions, though with a less concise API.