I had heard of it, but never checked until you mentioned it in this context. It seems that Elm is an entirely new language written atop JS (or maybe not, and targets JS?). A DSL.

DSLs also usually are an incomplete solution. Unless they themselves allow adhoc language creation using the DSL as a base. Common Lisp with its macros allows writing DSLs quite off-handedly as you program. You grow your program and language together as you get deeper into your problem.