In OOP, your basic unit of organization for code is the class. A frequently used methodology in Java, C# and similar languages is to organize your code around having one file for each class with the file name following the class name.

You can consider each of these class as a unit of organization to group a single concept.

These classes are in in namespaces which often follow the directory structure of the files in the solution/project. Namespaces are another level of organization.

How are large projects in functional languages typically organized?

How to you determine how to split your functions into different files?

Are other units of grouping beside files used?

How is code typically organized within a single file?