Document and test 'let-alist' support for indexing

* etc/NEWS: Announce 'let-alist' support for indexing.
* test/lisp/emacs-lisp/let-alist-tests.el (let-alist-numbers):
Add a test for 'let-alist's support for indexing.
* doc/lispref/lists.texi (Association Lists): Document indexing
with 'let-alist'.  (Bug#66509)

1 files changed, 13 insertions, 0 deletions

diff --git a/doc/lispref/lists.texi b/doc/lispref/lists.texi
index 37a07421e94..81edcc63d5b 100644
--- a/doc/lispref/lists.texi
+++ b/doc/lispref/lists.texi
@@ -1934,6 +1934,19 @@ Nested association lists is supported:
 Nesting @code{let-alist} inside each other is allowed, but the code in
 the inner @code{let-alist} can't access the variables bound by the
 outer @code{let-alist}.
+
+Indexing into lists is also supported:
+
+@lisp
+(setq colors '((rose . red) (lily . (yellow pink))))
+(let-alist colors .lily.1)
+     @result{} pink
+@end lisp
+
+Note that forms like @samp{.0} or @samp{.3} are interpreted as numbers
+rather than as symbols, so they won't be bound to the corresponding
+values in ALIST.
+
 @end defmac
 
 @node Property Lists