Oberon-F on classic Mac OS was really productive, and I imagine its descendant, BlackBox Component Pascal on Windows is so as well: one of the great features wa

Oberon-F on classic Mac OS was really productive, and I imagine its descendant, BlackBox Component Pascal on Windows is so as well: one of the great features was the ability to extend the IDE while running it: you could compile an extension and test it in seconds. Wirth knows how to design efficient languages and systems, and his students (most of the founders of Oberon microsystems, the developers of BlackBox, were such) carry on the tradition.