ProXL is an interface between Quintus Prolog and the X Window System (Version 11 Release 2 or later). ProXL permits the rapid development of X-based applications using Prolog's interactive development facilities. Essentially all functionality of X is made available through Prolog calls and callbacks. ProXL is built directly on the standard Xlib interface, and ProXL code is inter-operable with Xlib C code.

ProXL is not available under Windows.