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Re: [Scheme-reports] Fwd: Comments on draft 6 about call/cc
On Tue 21 Feb 2012 02:15, John Cowan <cowan@x> writes:
> An exceptional exit is simply a non-local exit from an exception handler.
> It's not particularly obvious when this is happening.
What's wrong with something like this?
(define (call-with-input-file filename proc)
(let ((port (open-input-file filename)))
(call-with-values (lambda () (proc port))
(apply values vals)))))))
> `Guard` works by capturing its continuation and setting a handler that
> captures the continuation at the point of raise. The guard continuation
> is then restored, which gives us the outer dynamic environment, and the
> cond-clauses are executed. If we fall off the end of the cond-clauses,
> the point-of-raise continuation is restored (giving us the inner dynamic
> environment) and the condition object is reraised.
This is expensive (reifying continuations for exceptional control-flow)
and error-prone (giving dynamic-wind workouts, and preventing exception
handling within run-once blocks).
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