So, let's give Elm a try... and it's not available on OpenBSD. Luckily it seems to just be a big old Haskell program. A program that can be build with Cabal. Ah yes, Haskell and Cabal... Yeah I don't know either.
Anyway, how hard can it be to build. Browsing around the net suggests that the following should build Elm.
$ doas pkg_add ghc $ doas pkg_add cabal-install $ git clone -b 0.19.1 https://github.com/elm/compiler.git $ cd compiler $ rm worker/elm.cabal $ cabal new-update $ cabal new-configure $ cabal new-build $ ./dist-newstyle/build/x86_64-openbsd/ghc-8.10.3/elm-0.19.1/x/elm/build/elm/elm --version 0.19.1
It seems to work, now I just need to learn Elm.