The code is nice, but putting it in a BEGIN block probably won't work. Just put it in the body of the module.

You want to have actually compiled your module before running that code (so the functions are defined), and run that before the person using your module imports stuff. Well the order of compilation is that they hit the use in their code, they call require, your code is compiled, your code is run, then they call import, then they continue compiling. So from their point of view, ordinary code in your module already is in a BEGIN block. :-)