## 9.1 Overview of the Interface

A special include file called `SWI-Prolog.h` should be included with each C-source file that is to be loaded via the foreign interface. The installation process installs this file in the directory `include` in the SWI-Prolog home directory (`?- current_prolog_flag(home, Home).`). This C-header file defines various data types, macros and functions that can be used to communicate with SWI-Prolog. Functions and macros can be divided into the following categories:

- Analysing Prolog terms
- Constructing new terms
- Unifying terms
- Returning control information to Prolog
- Registering foreign predicates with Prolog
- Calling Prolog from C
- Recorded database interactions
- Global actions on Prolog (halt, break, abort, etc.)