>You have to use a different set of operators to get modular arithmetic semantics. So, the choice is not a flag you flip at build time, but a choice of operators.

Like Zig I think.

As for 'panic at overflow' I think that Erlang/Elixir is the same so there are probably a lot of 'design patterns'/libraries to get inspiration from there.

One note, your language allow usage of 'named parameters' as in "return File(handle => ptr);" so this means that the name of the parameter is part of the API and must be chosen carefully.. ptr isn't a very good name, handle would be a better name, but then of course you have "return File(handle => handle);" which is a classic problem of named parameters..