/proc/testing()
world.xyzzy = 99
world.loop_checks = 42
return
The second line throws a compile error since xyzzy is not defined, but the third line will only error at runtime.
Considering the compiler knows about const-ness in some way, and already checks all var accesses with "." to make sure they're defined, would it be feasible to check if they're consts there as well?