Abdulaziz Ghuloum and R. Kent Dybvig, Implicit Phasing for R6RS Libraries, Proc.
ICFP 2007.
The forthcoming Revised Report on Scheme differs from previous reports in that the language it describes is structured as a set of libraries.
It also provides a syntax for defining new portable libraries. The same library may export both procedure and hygienic macro definitions, which allows procedures and syntax to be freely intermixed, hidden, and exported.