Warren Abstract Machine

In 1983, David H. D. Warren designed an abstract machine for the execution of Prolog consisting of a memory architecture and an instruction set [War83]. This design became known as the Warren Abstract Machine (WAM) and has become the de facto standard for implementing Prolog compilers. In [War83], Warren describes the WAM in a minimalist s style, making understanding very difficult for the average reader, even with a foreknowledge of Prolog s operations. Too much is left untold, and very little is justified in clear terms.1 This has resulted in a very scant number of WAM aficionados who could boast understanding the details of its workings.