Scheme as an idea goes way back, but the version of Scheme used by SICP 2e is about as old (young?) as Python is -- both made their initial appearances in the v

Scheme as an idea goes way back, but the version of Scheme used by SICP 2e is about as old (young?) as Python is -- both made their initial appearances in the very early 90s. And just like Python hasn't stood still in those 25 years, neither has Scheme, having had three further updates to the definition and quite a lot of research in areas such as hygienic macros and composable continuations, among other things, which make appearances in various implementations (but especially Racket... those guys have a habit of implementing pretty much every paper about Scheme...)