New: protocol for iteration with structs.

* lib.c (seq_iterable): Return t if argument is a structure
supporting the iter-begin method.
(seq_iter_get_oop, seq_iter_peek_oop, seq_iter_get_fast_oop,
seq_iter_peek_fast_oop): New static functions.
(seq_iter_init_with_info): Handle COBJ case. If the COBJ is a
structure which suports the iter-begin method, then retrieve
the iterator object by calling it, and then prepare the
iterator structure for either the fast or the canonical
protocol based on whether the iterator supports iter-more.
(seq_iter_mark): Mark the iter member if the iterator is a
struct object.
(iter_begin): Rearrange tests here to check object type first
before sequence kind. If the object is a structure supporting
the iter-begin method, then call it and return its value.
(iter_more, iter_step): Check for struct object with
corresponding special methods and return.
(iter_reset): Similar change like in iter_begin. We check for
the iter-reset special method and try to use it, otherwise
fall back on the regular iter_begin logic.

* lib.h (struct seq_iter): New member next of the ul union
for caching the result of a peek operation.

* struct.c (iter_begin_s, iter_more_s, iter_item_s,
iter_step_s, iter_reset_s): New symbol variables;
(special_sym): Pointers to new symbol variables added to
array.
(struct_init): New symbol variables initialized.
(get_special_required_slot): New function.

* struct.h (iter_begin_s, iter_more_s, iter_item_s,
iter_step_s, iter_reset_s): Declared.
(enum special_slot): New enum members iter_begin_m,
iter_more_m, iter_item_m, iter_step_m, iter_reset_m.
(get_special_required_slot): Declared.

* txr.1: Documented.

* tests/012/oop-seq.expected: New file.

* tests/012/oop-seq.tl: New file.

1 files changed, 21 insertions, 1 deletions

diff --git a/struct.c b/struct.c
index e12ffcec..2b76c510 100644
--- a/struct.c
+++ b/struct.c
@@ -105,9 +105,12 @@ val slot_s, derived_s;
 
 val nullify_s, from_list_s, lambda_set_s;
 
+val iter_begin_s, iter_more_s, iter_item_s, iter_step_s, iter_reset_s;
+
 static val *special_sym[num_special_slots] = {
   &equal_s, &nullify_s, &from_list_s, &lambda_s, &lambda_set_s,
-  &length_s, &car_s, &cdr_s, &rplaca_s, &rplacd_s
+  &length_s, &car_s, &cdr_s, &rplaca_s, &rplacd_s,
+  &iter_begin_s, &iter_more_s, &iter_item_s, &iter_step_s, &iter_reset_s
 };
 
 static val struct_type_hash;
@@ -141,6 +144,12 @@ void struct_init(void)
   nullify_s = intern(lit("nullify"), user_package);
   from_list_s = intern(lit("from-list"), user_package);
   lambda_set_s = intern(lit("lambda-set"), user_package);
+  iter_begin_s = intern(lit("iter-begin"), user_package);
+  iter_more_s = intern(lit("iter-more"), user_package);
+  iter_item_s = intern(lit("iter-item"), user_package);
+  iter_step_s = intern(lit("iter-step"), user_package);
+  iter_reset_s = intern(lit("iter-reset"), user_package);
+
   struct_type_hash = make_hash(nil, nil, nil);
   slot_hash = make_hash(nil, nil, t);
   slot_type_hash = make_hash(nil, nil, nil);
@@ -1932,6 +1941,17 @@ val get_special_slot(val obj, enum special_slot spidx)
   return get_special_static_slot(si->type, spidx, slot);
 }
 
+val get_special_required_slot(val obj, enum special_slot spidx)
+{
+  val content = get_special_slot(obj, spidx);
+  if (content == nil) {
+    val slot = *special_sym[spidx];
+    uw_throwf(error_s, lit("~s is missing required ~s slot"),
+              obj, slot, nao);
+  }
+  return content;
+}
+
 val get_special_slot_by_type(val stype, enum special_slot spidx)
 {
   struct struct_type *st = coerce(struct struct_type *, stype->co.handle);