cat-str/join/join-with: allow nested sequences

The measure/allocate/catenate functions which underlie
the cat-str implementation are streamlined, simplifying
the code. At the same time, they handle nested sequences
of string/character items.

* lib.c (struct cat_str): New member, seen_one. This flips
from 0 to 1 after the first item has been seen in the
cat_str_measure pass or cat_str_append pass. Each item
other than the first is preceded by a separator.
(cat_str_measure, cat_str_append): The more_p argument
is dropped. We account for the separator with the help
of the new seen_one flag, which allows us to easily
recurse over items that are sequences.
(cat_str_alloc): Reset the seen_one flag in preparation
for the cat_str_append pass.
(cat_str, vscat, scat2, scat3, join_with): Simplified.

* tests/015/split.tl: New tests.

* txr.1: Redocumented.

1 files changed, 13 insertions, 0 deletions

diff --git a/tests/015/split.tl b/tests/015/split.tl
index 15b3f2a7..1cb13647 100644
--- a/tests/015/split.tl
+++ b/tests/015/split.tl
@@ -298,3 +298,16 @@
   (spln 2 "," "a,b,c") ("a" "b" "c")
   (spln 3 "," "a,b,c") ("a" "b" "c")
   (spln 4 "," "a,b,c") ("a" "b" "c"))
+
+(mtest
+  (cat-str '()) ""
+  (cat-str '() "-") ""
+  (cat-str '(()) "-") ""
+  (cat-str '((()) ()) "-") ""
+  (cat-str '((()) #()) "-") ""
+  (cat-str '((("a" ("b")) #(#\c))) "-") "a-b-c")
+
+(mtest
+  (join-with "--" '()) ""
+  (join-with "--" '(("b"))) "b"
+  (join-with "--" '("b" #(("c") ()) "d")) "b--c--d")