parse/print libraries

doc/libraries.org

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+#+title: on libraries
+
+R⁷RS leaves it unspecified how exactly libraries correspond to files:
+
+#+begin_quote
+Programs and libraries are typically stored in files, although in some implementations they can be entered interactively into a running Scheme system. Other paradigms are possible. Implementations which store libraries in files should document the mapping from the name of a library to its location in the file system.
+#+end_quote
+
+thus the implementation of ~define-library~ is open to much interpretation. we could possibly define libraries as first-class objects, or deal with them statically. the former case is appealing to me, as it could massively simplify interactive use.