[eru]

Indeed. Getting these text based configuration tools work requires a lot of experience in language design.

Lots of tools become accidentally Turing complete, like Make. You need to plan these things from the start. If you want any computation possible at all, you need to be extremely vigilant, and base your language on firm foundations. See eg Dhall, a non-Turing complete configuration language (http://www.haskellforall.com/2016/12/dhall-non-turing-comple...).

If you are happy to get Turing completeness, you might want to write your tool as an embedded DSL and piggy-bank on an existing language, declarative or otherwise.