Allow customizing which exception types are show-stopping

lib/init-7.scm

@@ -1160,6 +1160,41 @@
 (define (raise-continuable exn)
   (raise (make-exception 'continuable "" exn #f #f)))
 
+;; Support continuing certain exception types at the top level, but
+;; still allow their subtypes to define themselves as serious and
+;; require exiting
+(define non-serious-exception-predicates '())
+(define serious-exception-predicates '())
+
+(define (register-non-serious-exception-predicate! pred)
+  (set! non-serious-exception-predicates (cons pred non-serious-exception-predicates)))
+(define (register-serious-exception-predicate! pred)
+  (set! serious-exception-predicates (cons pred serious-exception-predicates)))
+
+(define (default-exception-handler exn)
+  (%with-exception-handler
+   #f
+   (lambda ()
+     (define continuable-exception?
+       (and (exception? exn)
+            (eq? 'continuable (exception-kind exn))))
+     (define underlying-exn
+       (if continuable-exception?
+           (exception-irritants exn)
+           exn))
+     (if (and continuable-exception?
+              (find (lambda (f) (f underlying-exn))
+                    non-serious-exception-predicates))
+         (if (find (lambda (f) (f underlying-exn))
+                   serious-exception-predicates)
+             (raise underlying-exn)
+             (begin
+               (display "NON-SERIOUS EXCEPTION: " (current-error-port))
+               (write underlying-exn (current-error-port))
+               (display "\n" (current-error-port))))
+         (raise underlying-exn)))))
+(current-exception-handler default-exception-handler)
+
 (cond-expand
  (threads
   (define (%with-exception-handler handler thunk)

lib/srfi/35/internal.scm

@@ -204,6 +204,9 @@
 (define-condition-type/constructor &error &serious
   make-error error?)
 
+(register-non-serious-exception-predicate! condition?)
+(register-serious-exception-predicate! serious-condition?)
+
 ;; (chibi repl) support
 (define-method (repl-print-exception (exn condition?) (out output-port?))
   (define components (simple-conditions exn))

lib/srfi/35/internal.sld

@@ -6,7 +6,9 @@
           (scheme write)
           (only (chibi)
                 slot-ref
-                is-a?)
+                is-a?
+                register-non-serious-exception-predicate!
+                register-serious-exception-predicate!)
           (only (chibi repl) repl-print-exception)
           (only (chibi generic) define-method)
           ;; don’t let people go messing with a compound condition