lib: access special methods via special slot mechanism.

* ffi.c (ffi_flex_struct_in): Use get_special_slot to obtain
length method.

* lib.c (nullify_s, from_list_s, lambda_set_s): Definitions
removed from here.
(seq_info, car, cdr,  rplaca, rplacd, make_like, nullify,
replace_obj, length, empty, sub, ref, refset, dwim_set): Use
get_special_slot to obtain special method from object,
rather than maybe_slot.
(obj_init): Remove initializations of nullify_s, from_list_s
and lambda_set_s from here.

* struct.c (enum special_slot): Definition removed from here.
(nullify_s, from_list_s, lambda_set_s): Definitions moved here
from lib.c.
(special_sym): New static array.
(struct_init): Initializations of nullify_s, from_list_s
and lambda_set_s moved here from lib.c.
(get_special_slot): New function.

* struct.h (lambda_set_s): Declared.
(enum special_slot): Definition moved here.
(get_special_slot): Declared.

* txr.1: Added compat note, since get_special_slot behaves
like maybe_slot under 224 compatibility.

1 files changed, 10 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index 6bb2fc08..c2ee8823 100644
--- a/txr.1
+++ b/txr.1
@@ -69566,6 +69566,16 @@ of these version values, the described behaviors are provided if
 is given an argument which is equal or lower. For instance
 .code "-C 103"
 selects the behaviors described below for version 105, but not those for 102.
+.IP 224
+After \*(TX 224, the treatment of certain special structure functions
+has changed. Selecting 224 compatibility or lower restores that behavior.
+The specification given in the
+.B "Special Structure Functions"
+paragraph has always stated that special functions must be static slots,
+and that the behavior is unspecified if they are instance slots.
+The behavior of \*(TX 224 and earlier was that these functions worked anyway
+if they were instance slots; after \*(TX 224, they some special functions
+will no longer be recognized if bound to instance slots.
 .IP 222
 After \*(TX 222, the behavior of
 .code :vars