> From: Jim Blandy <xxxxxx@redhat.com>

    >   Another issue is that, if a collection could occur at any time, the
    >   values returned by macros like SCHEME_EXTRACT_VALUE_POINTER and
    >   EXTRACT_STRING can't be trusted long enough to be useful.  This can
    >   be solved in various ways; one idea is sketched in:

    >     http://sources.redhat.com/ml/guile/1999-01/msg00093.html

That (having a distinct free function and leaving sharing unspecified)
is a better idea than SCHEME_ALLOCATE_COPY_OF_* (and
SCHEME_EXTRACT_*).   It can be very efficient on systems where sharing
is easy.

-t