Frustration with HCL is why I wrote RCL (it now has a website, https://rcl-lang.org). It can generate HCL's json form for use with Terraform, and it has functions and sensible list comprehensions.
I also wrote BCL (https://github.com/wkhere/bcl) out of frustration with HCL :) (I didn't realize when starting it that the name "BCL" has some bad press for googlers though)
Your project looks very interesting, although we took quite different routes I guess, plus mine is at its quite early stage.