A multi-language programming environment, which includes the languagesPop-11, ML, Common Lisp and Prolog. It supports mixed-language programming and {incremental compilation} and includes a comprehensive {X Window system} interface. It is built on top of a two-stack {virtual machine}, PVM. POPLOG was developed at the University of sussex, Brighton, UK. ["POPLOG' s Two-Level Virtual Machine support for Interactive Languages", R. smith et al, in Research Directions in Cognitive science, v.5 (1992)].