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/struct.h b/struct.h
index d67ce3d7..385d8dd4 100644
--- a/struct.h
+++ b/struct.h
@@ -28,7 +28,16 @@
 extern val struct_type_s, meth_s, print_s, make_struct_lit_s;
 extern val init_k, postinit_k;
 extern val slot_s, derived_s;
+extern val lambda_set_s;
+
 extern struct cobj_ops struct_inst_ops;
+
+enum special_slot {
+  equal_m, nullify_m, from_list_m, lambda_m, lambda_set_m,
+  length_m, car_m, cdr_m, rplaca_m, rplacd_m,
+  num_special_slots
+};
+
 val make_struct_type(val name, val super,
                      val static_slots, val slots,
                      val static_initfun, val initfun, val boactor,
@@ -77,5 +86,6 @@ val slot_types(val slot);
 val static_slot_types(val slot);
 val slot_type_reg(val slot, val strct);
 val static_slot_type_reg(val slot, val strct);
+val get_special_slot(val obj, enum special_slot spidx);
 INLINE int obj_struct_p(val obj) { return obj->co.ops == &struct_inst_ops; }
 void struct_init(void);