prolog-system

prolog-system is a variable defined in `prolog.el'.
Its value is

nil

• Automatically becomes buffer-local when set.

Documentation:
Prolog interpreter/compiler used.
The value of this variable is nil or a symbol.
If it is a symbol, it determines default values of other configuration
variables with respect to properties of the specified Prolog
interpreter/compiler.

Currently recognized symbol values are:
eclipse - Eclipse Prolog
mercury - Mercury
sicstus - SICStus Prolog
swi - SWI Prolog
gnu - GNU Prolog

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.