If it is not Turing complete, your sandbox/interpreter/whatever can be certain that the code does not do anything "surprising". Basically, you can know at compi

If it is not Turing complete, your sandbox/interpreter/whatever can be certain that the code does not do anything "surprising". Basically, you can know at compile time that the program fulfills certain constraints. For practical examples, see the newish virtual machine inside of the linux kernel used to execute constraint "scripts" to control the firewall (https://lwn.net/Articles/740157/ https://lwn.net/Articles/740157/) Proving the same constraints and having the same trust in a Turing complete language is basically the halting problem, which is not computable.