А в самом r5rs что-нибудь есть об этом
Вот что нашел. Scheme, as defined in R5RS, does not have a full module system. However it does define the concept of a top-level environment. Such an environment maps identifiers (symbols) to Scheme objects such as procedures and lists. In other words, it implements a set of bindings.
Environments in R5RS can be passed as the second argument to eval