Am Do., 30. Apr. 2020 um 17:19 Uhr schrieb John Cowan <xxxxxx@ccil.org>:
>
> An important note is that the converter is called on the initial value of the parameter, on any new value set by invoking the parameter with one argument (in SRFI 39), and when the parameter is bound, but *not* when the binding is restored at the end of the `parameterize` expression.  This suits current-directory perfectly.  (Of course, if the directory being restored does not exist any more, an exception will be raised.)

How can restoring a parameter at the end of PARAMETERIZE raise an
exception? (Or, maybe, I didn't understand what you were saying?)