with-exception-handler

(with-exception-handler handler thunk)

Calls thunk with no arguments, with handler installed, and answers its value. An object raised inside thunk is passed to handler, which runs with the handlers outside this one in effect. For raise-continuable the handler's value is returned to the raise; for anything else the handler must leave by a continuation (call/cc) or raise, and returning is a secondary error.

Deviation: for an error a built-in procedure signals ((+ 1 'a)), the handler runs after thunk has been left -- the after thunks of the dynamic-winds inside it have run -- on every backend; R7RS runs it where the error happened. raise, raise-continuable and error call it where they stand.