High-performance Prolog compiler developed at LIACC/Universidade do Porto and at COPPE Sistemas/UFRJ. The YAP Prolog engine is based in the Warren Abstract Machine, with several optimizations for better performance. YAP follows the Edinburgh tradition, and is largely compatible with the ISO-Prolog standard and with Quintus and SICStus Prolog.

YAP features a constraint solver over real numbers, and support for constraint handling rules (CHR).