Code should be reusable. An expression traversing a data structure shouldn’t be written multiple times, it should be pulled out into a generic traversal function. At a larger scale, a random number generator shouldn’t be written multiple times, but rather pulled out into a module that can be used by others. It is important that such abstractions must be done carefully. Often times a type is visible to the caller, and if the type is not handled carefully the abstraction can leak. For examp...
