SWI-Prolog 9.2.9 Reference Manual: Section B.10

## B.10 Hooks for loading files

All loading of source files is achieved by load_files/2. The hook prolog_load_file/2 can be used to load Prolog code from non-files or even load entirely different information, such as foreign files.

prolog_load_file(+Spec, +Options)
  Load a single object. If this call succeeds, load_files/2 assumes the action has been taken care of. This hook is only called if Options does not contain the `stream(Input)` option. The hook must be defined in the module `user`.

  This can be used to load from unusual places as well as dealing with Prolog code that is not represented as a Prolog source text (for example some binary representation). For example, library `library(http/http_load)` loads Prolog directly from an HTTP server. See also prolog:open_source_hook/3, which merely allows for changing how a physical file is opened.

prolog:open_source_hook(+Path, -Stream, +Options)
  This hooks is called by the compiler to overrule the default open/3 call `open(Path, read, Stream)`. Options provide the options as provided to load_files/2. If the hook succeeds compilation continues by loading from the returned (input) stream. This hook is particularly suited to support running the code to a preprocessor. See also prolog_load_file/2.
prolog:comment_hook(+Comments, +Pos, +Term)
  This hook allows for processing comments encountered by the compiler. If this hook is defined, the compiler calls read_term/2 with the option `comments(Comments)`. If the list of comments returned by read_term/2 is not empty it calls this comment hook with the following arguments.

  - Comments is the non-empty list of comments. Each comment is a pair Position-String, where String is a string object (see section 5.2) that contains the comment including delimiters. Consecutive line comments are returned as a single comment.
  - Pos is a stream-position term that describes the starting position of Term
  - Term is the term read.

  This hook is exploited by the documentation system. See stream_position_data/3. See also read_term/3.