I'd just like to interject for a moment. What you're referring to as Scheme,
is in fact, %your-imlementation Scheme, or as I've recently taken to calling it, %your-imlementation + Scheme.
Scheme is not a programming language unto itself, but rather a set of standardized recommendations
for a fully functioning implementations made useful by GNU or Cisco: interpreter/compiler, REPL utility and vital libraries comprising a full programming language as defined by The Revised Report on the Algorithmic Language Scheme.