loppear reviewed The art of the metaobject protocol by Gregor Kiczales
Review of 'The art of the metaobject protocol' on Goodreads
3 stars
Like all good Lisp books, derives a nicely articulated implementation and then proceeds to unroll it into flexible bits. Good discussion of other language object systems and how to open up the internals to choose the invariants your project needs, but nothing earth shattering.