I would say that ATL is a domain-specific language (DSL). To be more accurate, I would refer to it as a horizontal DSL (as opposed to typical DSLs, which are usually focused on some vertical subject domain or industry). Another thought is that, if I were writing HPC-focused software today (and, especially, tomorrow), I would definitely much prefer Julia to ATL or similar niche solutions. Thanks to (likely) not much of, if any, loss of performance, but an incomparably wider spectrum of potential applications and covered domains. Plus, an additional benefit of lack of the two-language problem.