Lisp functions are generally not pure! Common lisp, the language this article is mostly talking about, is very comfortable with state. CL, like most lisps, ofte

Lisp functions are generally not pure! Common lisp, the language this article is mostly talking about, is very comfortable with state. CL, like most lisps, often encourages a functional style- everything is an expression, and usually you'll return data structures even if you mutate them. But big hash tables and arrays are definately in common lisp's wheelhouse. Even Clojure, which is largely pure when dealing only with itself, has full support for diving into the messy practicalities of mutation on the JVM.