The recommended practice is to define macros or functions in modules and then call the macro or function. It is not good practice to use module includes as function calls. Including a module should not do more than defining functions and macros and discovering programs, libraries, and paths. The actual include command should not define or modify variables and the reason for this is that a repeated include, which may be accidental, should not introduce any unwanted side effects. In Recipe 5, Redefining functions and macros, we will create a guard against accidental includes.