The HOPL series produces accurate historical records and descriptions of programming language design, development, and philosophy. HOPL-IV wll be only the 4th HOPL. Previous HOPLs occurred in 1978, 1993, and 2007. HOPL papers can be quite long. As the HOPL-IV call for papers says, “Because of the complex nature of the history of programming languages, there is no upper bound on the length of submitted papers—authors should strive for completeness”. HOPL papers are often authored by the original designers of an important language or individuals who have made significant contributions to the evolution of a language.