Scheme implementation of Ruse, a simple interpreted language based on
substitution rules. Evaluating an expression involves checking the expression
against a database of rules. Each rule specifies a pattern that must be
matched, and an expression specifying the result if the match is made. Pattern
matching can involve binding parts of the expression to variable names, which
can be referred to in the result

Tested under:
MzScheme v4.1.5 (Ubuntu Linux 9.10)