seq_build: convert list buiding to list_collect.

We want to use the list_collect functions for consistency.
For instance, these functions allow an atom to be added
to an improper list if the terminating atom is a sequence.
(append '(1 . "abc") "d") yields (1 . "abcd").

* lib.h (struct seq_build): New member, tail.

* lib.c (seq_build_list_add): Use list_collect.
(seq_build_list_pend): Use list_collect_nconc.
(seq_build_list_finish): Nothing to do here, except
call seq_build_convert_to_finished since bu->obj
is the head of the list at all times now.
(seq_build_improper_add, seq_build_improper_pend):
Functions removed.
(sb_improper_ops): Structure removed.
(seq_build_convert_to_improper): Function removed.
(seq_build_convert_to_list): Different strategy needed
here now. The list just goes into bu->obj, and we have
to set up the tail to either point to the last cons
cell's cdr, or else to bu->obj if the list is empty.
(seq_build_init): Initialize bu->tail in the three cases
that set up list collection.

1 files changed, 1 insertions, 0 deletions

diff --git a/lib.h b/lib.h
index a6e4869e..f254ce6b 100644
--- a/lib.h
+++ b/lib.h
@@ -471,6 +471,7 @@ struct seq_iter_ops {
 
 typedef struct seq_build {
   val obj;
+  loc tail;
   val self;
   union {
     val from_list_meth;