C.2.1.1 Loading XSB source files

SWI-Prolog's emulation of XSB depends on the XSB preferred file name extension .P. This extension is used by library(dialect/xsb/source) to initiate a two phase loading process based on term_expansion/2 of the virtual term begin_of_file.

1. In the first phase the file is read with XSB compatible operator declarations and all directives (:- Term) are extracted. The directives are used to determine that the file defines a module (iff the file contains an export/1 directive) and construct a SWI-Prolog compatible module declaration. As XSB has a two phase compiler where SWI has a single phase compiler, this is also used to move some directives to the start of the file.

2. The second phase loads the file as normal.

To load a project in both XSB and SWI-Prolog it is advised to make sure all source files use the .P file name extension. Next, write a SWI-Prolog loader in a .pl file that contains e.g.,

:- use_module(library(dialect/xsb/source)).

:- [main_file].

It is also possible to put the able use_module/1 directive in your personal initialization file (see section 2.2), after which XSB files can be loaded as normal SWI-Prolog files using

% swipl file.P

XSB code may depend on the gpp preprocessor. We do not provide gpp. It is however possible to send XSB source files through gpp by loading library(library/dialect/xsb/gpp). This require gpp to be accessible through the environment variable PATH or the file_search_path/2 alias path. We refer to the gpp library for details.