status: final (2017/8/8)
macros is hard because they do not compose well: The arguments of a macro
expansion are not expanded. This SRFI defines an easy to comprehend
high-level system for writing powerful, composable (or eager)
macros, two of whose defining features are that its macro arguments are
(in general) eagerly expanded and that it can be portably implemented in
any Scheme implementation conforming to the R7RS.