Safe With Handler
;; From the chapter "Condition system" in "The Nearly Complete
;; Scheme48 Reference Manual" by Taylor Campbell:
;; *Warning:* `With-handler' is potentially very dangerous. If an
;; exception occurs and a condition is raised in the handler, the
;; handler itself will be called with that new condition!
;; Furthermore, the handler may accidentally return to an unexpecting
;; signaller, which can cause very confusing errors. Be careful with
;; `with-handler'; to be perfectly safe, it might be a good idea to
;; throw back out to where the handler was initially installed before
;; doing anything.
;; The following is what he then suggests.
;; ,open handle
(define (with-handler/safe handler thunk)
(lambda (kond propagate)
(k (lambda () (handler kond propagate))))
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