search, rsearch: rewrite using seq_info and bugfix.

* lib.c (seq_getpos, seq_setpos): New functions.

* lib.h (seq_getpos, seq_setpos): Declared.
(search_list, rsearch_list): Static functions removed.
(search_common): New static function.
(search, contains, rsearch): These functions are now trivial
wrappers around search_common. A requirement problem is fixed
in rsearch: when the key is empty, the length of sequence is
returned rather than zero, because zero is obviously not the
right most place where an empty key matches.

* txr.1: Documentation updated.

1 files changed, 16 insertions, 4 deletions

diff --git a/txr.1 b/txr.1
index 1afe9b7c..5b531ab5 100644
--- a/txr.1
+++ b/txr.1
@@ -29782,12 +29782,11 @@ The arguments
 .meta haystack
 and
 .meta needle
-are sequences: lists, vectors
-or strings, in any combination.
+are sequences. They may not be hash tables.
 
 If
 .meta needle
-is not empty, then occurs at some position N within
+is not empty, then it occurs at some position N within
 .meta haystack
 if
 the first element of
@@ -29865,7 +29864,9 @@ The
 .code rsearch
 function is like
 .code search
-except that if
+except for two differences.
+
+Firstly, if
 .meta needle
 matches
 .meta haystack
@@ -29874,6 +29875,17 @@ in multiple places,
 returns the right-most matching position rather than
 the leftmost.
 
+Secondly, if
+.meta needle
+is an empty sequence, then
+.code rsearch
+returns the length of
+.codn haystack ,
+thereby effectively declaring that the rightmost match for an empty
+.meta needle
+key occurs at the imaginary position past the element of
+.metn haystack .
+
 .coNP Functions @ ref and @ refset
 .synb
 .mets (ref < seq << index )