What does this bit of code do?

[Rob MacLachlan <RAM@>]

    Date: Monday, 2 March 1987  12:26-EST
    From: sandra%utah-orion at utah-cs.arpa (Sandra J Loosemore)
    To:   Kent M Pitman <KMP at scrc-stony-brook.arpa>
    Re:   What does this bit of code do?

    It occurs to me that one of the strangenesses of exiting from the cleanup
    forms of an unwind-protect is that CLtL requires throw to find a matching
    catch before proceeding to do anything, even though the throw might never
    actually return control to that catch!  Weird....

Actually this is required anyway, since in the case where the catch
tag is not found, the error is required to be signalled without having
processed any unwind protect cleanups or done any unwinding.  See the
Throw definition on page 142 in CLTL.

  Rob