There is no effect on performance based on function visibility. There were some reports that having a lot of public functions in a module slows down compilation time, but it actually has no effect on runtime performace, and if it does, it is a result of some limitation in current compiler implementation
Oh and
That type of optimizations is out of scope of current type-system work, I asked about that some time ago on the forum. I hope that at least the dot (.) operator will finally be optimized
