Modules give us a way to organize our functions (and other items that have names, such as data structures) into categories. This helps us keep things organized, and allows us to use the same name more than once, as long as we only use it once per module. It also lets us use shorter versions of a thing's name most of the time, but gives us a longer version we can use when those short names might be confusing or ambiguous.
Modules
Defining a module
Defining a module is easy. In any .rs file which the compiler is going to be looking at, we can use the mod keyword to start a new module. There are two different ways to use that keyword, though, depending on whether we want to define the module as a section of the current file...