zl:1 - FTP

607
unwind-protect-case
(unwi nd-protect protected-form
cleanup-form1
cleanup-form2
... )
protected-form is evaluated, and when it returns or when it attempts to quit
out of the unwind-protect, the cleanup-forms are evaluated. To ensure
that unwind-protect does not return without completely executing its
cleanup forms, macro sys:without-aborts is automatically and atomically
wrapped around all cleanup-forms, preventing them from being aborted by
user action.
unwind-protect catches exits caused by return-from or go as well as .those
caused by throw. The value of the unwind-protect is the value of
protected-form. Multiple values returned by the protected-form are
propagated back through the unwind-protect.
The cleanup forms are run in the variable-binding environment that you
would expect: that is, variables bound outside the scope of the
unwind-protect special form can be accessed, but variables bound inside
the protected-form cannot be. In other words, the stack is unwound to the
point just outside the protected-form, then the cleanup handler is run, and
then the stack is unwound some more .
. Note: It is almost never adequate to do something of the form
(unwind-protect (progn (faa) ... code ... )
(undo-faa»
Nearly always you should write
(let «old-faa-state (read-faa-state»)
(unwind-protect (progn (faa) ... code ... )
(set-faa-state old-faa-state»)
You should also consider that other processes may see your data structure
in the modified state. If you have a shared structure, you may need to use
a lock to only allow one process to use it while it is modified.
For a table of related items: See the section "N onlocal Exit Functions" in
Symbolics Common Lisp: Language Concepts.
unwind-protect-case (&optional aborted-p-var) body-form &rest Macro
cleanup-clauses
body-form is executed inside an unwind-protect form. The cleanup forms of
the unwind-protect are generated from cleanup-clauses. Each cleanupclause
is considered in order of appearance and has the form (keyword
forms ... J. keyword can be :normal, :abort or : always. The forms in a
:normal clause are executed only if body-form finished normally. The
I