It sounds like, with a little over two pages of Prolog, he had a prototype of a multi-threaded, message-passing DSL. With 1,100 lines of Prolog, he had the oth

It sounds like, with a little over two pages of Prolog, he had a prototype of a multi-threaded, message-passing DSL. With 1,100 lines of Prolog, he had the other Erlang elements such as process supervision groups, error trapping, tracing, etc. They eventually rewrote it in C to make it faster, to remove some counterproductive aspects of Prolog's semantics (in particular, logic variables were being instantiated across the threads), and to change the syntax a bit. There's a good interview with him on SE-Radio (http://se-radio.net/podcast/2008-03/episode-89-joe-armstrong-erlang http://se-radio.net/podcast/2008-03/episode-89-joe-armstrong...) that discusses the original implementation, as well.