Comment by chrisshroba

This seems like more of an issue with porting an existing language than creating a new one. With the “can write to the file system” example, you would only need one version of a “writeJSON” function, for example, because writing without write access is nonsensical. Then you’d specify exactly what you need through these constraints, and if they weren’t met, you couldn’t call the function. This already exists and works well when it comes to const-correctness in a language like C++. You can’t call a non-const method from a const one, for example, and this doesn’t lead to multiple versions of each function, because if a function mutates state, you know that it will never be able to be called from a const method.