In the 80s people were already developing multi-100kloc programs in Lisp. The operating system of the MIT Lisp Machine grew to something like 500kloc Lisp. Late

In the 80s people were already developing multi-100kloc programs in Lisp. The operating system of the MIT Lisp Machine grew to something like 500kloc Lisp. Later versions (end 80s) of it were more like 1.5MLOC of Lisp. Common Lisp was designed to be a successor of such a Lisp and was supposed to support both complex and/or large applications. Code density can be a bit higher than C++ (say, factor 3) for larger programs. In the end 80s / early 90s Evans&Sutherland developed a high-end 3d design software in mostly Lisp - the Conceptual Design and Rendering System (CDRS) - many of the cars at that time were designed with it (from Ford, Jaguar, German brands, ...). A designer work environment did cost most than a million USD per seat - including a high-end graphics system from E&S. The 3d software was written in atleast 150kloc C++ and 400kloc Lisp. Other CAD systems written in Lisp should have been much larger like iCAD or the design system from PTC (years ago to be said at 7MLOC Lisp). iCAD for example was used at Boeing for the development of turbines, wings, internal stuff - it's even said that there was a complete model of some Boeing in iCAD - which used kind of an object-oriented language on top of Lisp for the parametric construction of technical things. Similar applications and languages still exist - for example GenDL: https://gitlab.common-lisp.net/gendl/gendl https://gitlab.common-lisp.net/gendl/gendl There are a bunch of things which makes this possible: Lisp compilers with various compile-time warnings, extensive runtime error handling facilities, object-oriented programming, good development environments, ...