seq_iter: support reverse iteration for ranges.

* lib.h (seq_iter_t): Add some union members to ui and ul for
use with ranges. The purpose of this is to have separate
naming for the iteration variables for ranges.

* lib.c (seq_iter_get_range_cnum, seq_iter_peek_range_cnum,
seq_iter_get_range_chr, seq_iter_peek_range_chr,
seq_iter_get_range_bignum, seq_iter_peek_range_bignum): Use
new union member names for clarity.
(seq_iter_get_rev_range_cnum, seq_iter_peek_rev_range_cnum,
seq_iter_get_rev_range_chr, seq_iter_peek_rev_range_chr,
seq_iter_get_rev_range_bignum,
seq_iter_peek_rev_range_bignum): New static functions.
(seq_iter_with_init_info): Drop obj argument since the si
argument has the object. Add handling for empty and reversed
ranges. Also convert unbounded ranges like N..t and N..: to
just N, recursively. Use new union member names.
(seq_iter_init, seq_iter_init_with_rewind, iter_begin,
iter_reset): Follow elimination of argument in
seq_iter_init_with_info.

1 files changed, 4 insertions, 1 deletions

diff --git a/lib.h b/lib.h
index 9eb0510b..770fefc7 100644
--- a/lib.h
+++ b/lib.h
@@ -390,10 +390,13 @@ typedef struct seq_iter {
   union {
     val iter;
     cnum index;
+    val vn;
+    cnum cn;
   } ui;
   union {
-    val lim;
     cnum len;
+    val vbound;
+    cnum cbound;
   } ul;
   int (*get)(struct seq_iter *, val *pval);
   int (*peek)(struct seq_iter *, val *pval);