One of the biggest complaints of Elm is the lack of typeclass. I'm not aware of a similar abstraction in OCaml. Does Reason have similar limitations, or are there ways to get around it?

OCaml has parametrized modules, confusingly called functors, a very nice feature along with first class modules that Haskell doesn’t have. It is roughly speaking used wherever one would use a Typeclass in Haskell http://ocamlgraph.lri.fr/index.en.html is one good example.

Noon question: what is a typeclass in the sense of the feature Elm lacks?

Does it mean the equivalent to `class` keyword in the OO sense?

From an OO perspective, Elm lacks interfaces. Typeclasses are probably the best way to handle the idea of interfaces in the functional programming model.

Since functions are first class, you can bodge this with an object that has functions in it, but since those don't serialize they don't play well with a lot of Elm idioms if you put them in your model.

I thought about this, and kinda came to a conclusion, than I would take a language that has generics, and doesn't have interfaces (i.e. Elm) over a language that has interfaces and doesn't have generics (i.e. Go)

typescript has both :D

Well, in my professional life, there is a lot of untyped Python on the horizon :P

And for side-projects I think I prefer PureScript anyway?

First class modules. And yes, not having typeclasses is a bit of a turn off too...