@dcz late to the thread, but I am a recent follower of Prolog. https://www.swi-prolog.org seems to have threaded execution, not sure whether it is implicitly parallel under the hood. But why not gorge on bountiful free/open software? Write Prolog that generates a Makefile and run it with 'make -j $CORES' ? Or run many Prolog instances (pengines?) designed in a control hierarchy?