Just to add a bit to that, since not many people know this part... Joe Armstrong and S.R. Virding wrote a case study chapter for the book, "Strand: New Concept

Just to add a bit to that, since not many people know this part... Joe Armstrong and S.R. Virding wrote a case study chapter for the book, "Strand: New Concepts in Parallel Programming," and it has a section explaining the history of Erlang up to 1990. The first Erlang prototype, written in Prolog, ran into performance problems with backtracking and emulated concurrency, so it was ported to a Parlog system (a parallel Prolog) written by S.R. Virding. The Parlog implementation was still too slow, so a third implementation was created that compiled Erlang into Strand88, a commercial product from Strand Software Technologies, Inc. which claimed to be the first commercial parallel logic programming language. That implementation was finally fast enough that Erlang could be used outside of the Computer Science Lab at Ericson. Presumably at some point after that it was re-written at least one more time...