3.1.1.1 File Name Extensions

The first consideration is what extension to use for the source files. Tradition calls for .pl, but conflicts with Perl force the use of another extension on systems where extensions have global meaning, such as MS-Windows. On such systems .pro is the common alternative. On MS-Windows, the alternative extension is stored in the registry key HKEY_CURRENT_USER/Software/SWI/Prolog/fileExtension or HKEY_LOCAL_MACHINE/Software/SWI/Prolog/fileExtension. All versions of SWI-Prolog load files with the extension .pl as well as with the registered alternative extension without explicitly specifying the extension. For portability reasons we propose the following convention:

If there is no conflict

because you do not use a conflicting application or the system does not force a unique relation between extension and application, use .pl.

With a conflict

choose .pro and use this extension for the files you want to load through your file manager. Use .pl for all other files for maximal portability.