[geokon]

I'm not familiar with Haskell so it's hard for me to say. A cursory look at the wiki.. I get the impression you'd need to explicitly create a new type class? In a dynamic language you can just "dynamically" extend the record (which is sort of like a "class) with new interfaces without making a new class type.

Hopefully that helps.. Sorry if it's not exactly helpful

The protocol example at the end shows how it's done

https://eli.thegreenplace.net/2016/the-expression-problem-an...

If you write something like

    (extend-type BinaryPlus
      Evaluatable
        (evaluate [this] (+ (evaluate (:lhs this)) (evaluate (:rhs this)))))

Then you are adding (and defining) the Evaluatable interface to a record BinaryPlus (which can be coming from a different library and already be implementing other interfaces)

BinaryPlus records can still be used where they were used previously, but you can also use them with the enhancement you added

[wtetzner]

Clojure's protocols are basically the dynamic language equivalent of type classes.

> I get the impression you'd need to explicitly create a new type class?

In the same way you need to use defprotocol in Clojure. You can implement existing type classes on types without defining a new type class.