The author realized their mental model of setf was incorrect, as Lisp allows for defining new setf forms for assignment, utilizing a macro structure that accesses the structure of its arguments but not their values. This flexibility allows for defining new specializations, such as setting the head of a list or specializing based on the type of the new value. Additionally, the author discusses constructing setf-like macros using generic functions and synthesizing function names, showcasing the power and flexibility of Lisp without the need for special machinery. Overall, the article provides a deeper understanding of setf and its underlying mechanisms.
https://simondobson.org/2024/07/27/my-mental-model-of-setf-was-wrong/