In computer science, a module is a self-contained subunit of a program that interacts with other modules via a well-defined interface. Modules in C++ typically consist of a pair of code files, named such as foo.cc and foo.h. Arachne is no exception: its source code consists almost completely of modules defined in this way. Some modules are executable, meaning they can be run at a command line or in script modules. Modularity is the principal design feature of Arachne.
Each module name (e.g., Module) corresponds to a file of the form Module.cc in one of the directories of the Arachne code package. In the case of executable modules, the name also corresponds to the name of a compiled executable in ARACHNE_BIN_DIR, which can be run on the command line.