Before you understand how reloading works in Fennel, you need a little background regarding Lua’s module system, since Fennel is just a compiler that emits Lua code. Older versions of Lua had a module function which would declare the whole rest of the file as being part of a specific module and register that with the module system, and all functions that would normally be declared as global within that file would be exported as part of the module instead. But in version 5.1, that system was recognized as redundant: nowadays a module is just a file that returns a table1 with closures and other values in it. This is reflects the relentless simplicity behind the design of Lua; why have modules as their own concept when tables and closures can do just as good a job?