[badfrog]

From that chapter: "In general, a method for combining data values satisfies the closure property if the result of combination can itself be combined using the same method."

It sounds like they're just describing recursive data structures? When most people talk about closures, aren't they referring to this (from Wikipedia)?

"In programming languages, a closure, also lexical closure or function closure, is a technique for implementing lexically scoped name binding in a language with first-class functions. Operationally, a closure is a record storing a function[a] together with an environment."

EDIT: My SICP quote was actually from somebody's notes, not the book itself. But the point remains.