Takeshi Abe scripsit:

> Just a minor point, but can the idiom code be:
> (let ((key (ephemeron-key ephemeron)))
>   (if (ephemeron-broken? ephemeron-broken)
>       ... broken case ...
>       (let ((datum (ephemeron-datum ephemeron)))
>         ... code using key and datum ...)))
> in order to spare the useless access to datum when the ephemeron
> has already been broken?

Unfortunately the answer is no.  In a system where GC runs in a separate
thread, the ephemeron may break after calling ephemeron-broken? and
before calling ephemeron-datum.  You really do have to capture both
key and datum first.

--
John Cowan          http://www.ccil.org/~cowan        xxxxxx@ccil.org
I now introduce Professor Smullyan, who will prove to you that either
he doesn't exist or you don't exist, but you won't know which.
                               --Melvin Fitting