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The problem with turing-complete config languages, is not that it might take long to evaluate them. The problem is they are hard to modify by programs. A purely data-driven configuration, e.g. an ini-style config file, json, or xml is relatively easy to parse, transform and unparse again. Doing that with a config file written in a Turing-complete language is substantially harder, theoretically even impossible. But in practice most configuration are evaluated from a subset of all programs. A language like Dhall tries to formalize that subset and and thereby enables better processing of such programs.