It's a very big deal, especially if you're actually implementing commercial Prolog solutions rather than toy code for learning or academic papers. SWI is histor

It's a very big deal, especially if you're actually implementing commercial Prolog solutions rather than toy code for learning or academic papers. SWI is historically quite slow and SWI's model of explicit threading control and other choices tends to degenerate Prolog code for SWI into quasi-procedural, script-like execution. Also, while not Prolog proper, certain commercial Prolog engines do have much more powerful facilities for constraint logic programming over the reals which make them a preferred choice in eg (legacy) financial optimization models.