http://srfi.schemers.org/srfi-34/srfi-34.html
Askemos did not have any exception handling system for quite some
time, because exception handling is not strictly nessesary.
But it is a practical thing and hence it's there.
Beginers beware: use exceptions with care.
Never have the normal computation raise any exceptions.
Normal cases should be handled with normal code.
Exceptions are intented to mark parts of the code
(the exception handler) as "seldom used"
and optimize the body part.