[hocuspocus]

> The thing is, it takes a bit of experience to appreciate why HKT are important, and typically you can only get this experience using Haskell.

They're fairly common in Scala too, and I believe in OCaml through modules.

[gpderetta]

And C++ if you squint hard enough.

[FrustratedMonky]

and F# with computations Seems common with functional programming, that it takes a mind-set change before seeing the need.