[unboxed_type]

> it's arguably better to work from a framework which guarantees that it won't be by construction... rather than attempting a game-of-operation where minor modifications to your program might seemingly randomly knock into undecidable-land.

I presume that a programming language is a compromise between expressiveness and decidability. Cost estimation feature is definitely a good one until having that feature stops you from being able to develop your business logic in a convenient-enough manner. Regarding the latter, I am not convinced that Simplicity is a nice fit.