INPUT
T_STRING_OR_NULL
    $var = SvPOK($arg) ? SvPV_nolen($arg) : NULL;

T_STRING_NON_NULL
    $var = SvPOK($arg) ? SvPV_nolen($arg) : (croak(\"$var cannot be undef\"), NULL);

T_GOBJECT_WRAPPER
    $var = ($type)gperl_get_object($arg);

T_XMLNODE
    $var = pv_to_xmlnode($arg);

T_GLIST_STRING
    $var = array_to_glist_string((AV*)SvRV($arg));

T_GLIST_GOBJECT
    $var = array_to_glist_gobject((AV*)SvRV($arg));
