Common Lisp's Tripartite Type System: Types, Classes, and the Machine's Truth

This article delves into the unique aspects of Common Lisp's type system. It's not simply static or dynamic, but a sophisticated interplay of types, classes, and underlying machine implementation. Types govern function call compatibility, struct field compatibility, and compiler optimizations; classes dictate method dispatch and OO inheritance; while the machine hides implementation details like type tags. Through examples, the article shows how Common Lisp balances the fluidity of dynamic languages with runtime and compile-time type checking and optimization, ultimately boosting debuggability and performance.