:- Yet Another Prolog



YAP is a high-performance Prolog compiler developed at LIACC/Universidade do Porto and at COPPE Sistemas/UFRJ. Its Prolog engine is based in the WAM (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 has been developed since 1985. The original version was written in assembly, C and Prolog, and achieved high performance on m68k based machines. The assembly code was used to implement the WAM emulators. Later emulators supported the VAX, SPARC, and MIPS architectures. Work on the more recent version of YAP strives at several goals:

YAP 4.0 and early versions of YAP 4.1 were distributed under a license that enables free use in academic environments. From Yap4.1.15 onwards YAP is distributed under Perls's Artistic license. We would like to follow an open development model: sources to the system are always made available from the home page, and contributions from users are most welcome!

Mirrors of this page are available at sourceforge, at Universidade do Porto, and at Universidade Federal do Rio de Janeiro (the one in Rio currently has problems).