[comex]

Technically, it’s not just Scheme-like but literally a Scheme interpreter (TinyScheme). However, the Scheme isn’t being executed to make individual sandboxing decisions. It’s just executed once while parsing the config, to build up a binary sandbox definition which is what the kernel ultimately uses to make decisions (using a much more limited-purpose, non-Turing-complete execution engine).

[selridge]

Do we know that engine is not Turing-complete for sure?

[VogonPoetry]

The runtime engine is not known to be turning complete. It has no expressions and cannot loop, only forward jumps are permitted.