It seems that FIRRTL is designed to be the LLVM of hardware programming. If Scala is not your cup of tea, the co-designer of FIRRTL, Patrick Li has designed a new optionally type programming language Stanza that is more expressive for this kind of work. FYI, the designers of FIRRTL then went to start Jitx, a circuit design automation company using Stanza to perform circuit design automation. Alternatively, if you prefer a more established language than Stanza, dlang can be a great substitute for Scala: https://dconf.org/2017/talks/marques.html