I outfitted `rest` with some error reporting and tried out exception
handling. So far so good.
One issue is that the dictionary is not a persistent datastructure, so
if there was an "inscribe" command (it's not yet implemented for this
Scheme implementation) that might be slightly problematical. (If an
error were to occur in an evaluation that had already entered new
definitions into the dict then those definitions would "survive" into
the rest of the REPL session (or whatever.))
I'll look into persistent dict for Scheme.
b116c2c98b