I am going to make a PR myself for the main document. Using a custom
evaluator, as in Daphne's proposal, has the issue that some global
state (like the state of threads) is initialised anew for each
evaluation. Of course, it is possible to write a REPL that acts within
the dynamic extent of the `run' procedure but this is out of the scope
of SRFI 226. That said, I am fine with others adding code to this SRFI
in a `contrib/' subdirectory.