Add macro seq-setq.

* doc/lispref/sequences.texi (seq-setq): Document this macro.

* lisp/emacs-lisp/seq.el (seq-setq): New macro.

* test/lisp/emacs-lisp/seq-tests.el (test-seq-setq):
Test this macro (bug#50053).

doc/lispref/sequences.texi

@@ -1111,6 +1111,23 @@ The @code{pcase} patterns provide an alternative facility for
 destructuring binding, see @ref{Destructuring with pcase Patterns}.
 @end defmac
 
+@defmac seq-setq var-sequence val-sequence
+@cindex sequence destructuring
+  This macro works similarly to @code{seq-let}, except that values are
+assigned to variables as if by @code{setq} instead of as in a
+@code{let} binding.
+
+@example
+@group
+(let ((a nil)
+      (b nil))
+  (seq-setq (_ a _ b) '(1 2 3 4))
+  (list a b))
+@result{} (2 4)
+@end group
+@end example
+@end defmac
+
 @defun seq-random-elt sequence
   This function returns an element of @var{sequence} taken at random.
 

lisp/emacs-lisp/seq.el

@@ -93,6 +93,14 @@ name to be bound to the rest of SEQUENCE."
   (declare (indent 2) (debug (sexp form body)))
   `(pcase-let ((,(seq--make-pcase-patterns args) ,sequence))
      ,@body))
+
+(defmacro seq-setq (args sequence)
+  "Assign to the variables in ARGS the elements of SEQUENCE.
+
+ARGS can also include the `&rest' marker followed by a variable
+name to be bound to the rest of SEQUENCE."
+  (declare (debug (sexp form)))
+  `(pcase-setq ,(seq--make-pcase-patterns args) ,sequence))
 
 
 ;;; Basic seq functions that have to be implemented by new sequence types

test/lisp/emacs-lisp/seq-tests.el

@@ -383,6 +383,30 @@ Evaluate BODY for each created sequence.
       (should (null b))
       (should (null c)))))
 
+(ert-deftest test-seq-setq ()
+  (with-test-sequences (seq '(1 2 3 4))
+    (let (a b c d e)
+      (seq-setq (a b c d e) seq)
+      (should (= a 1))
+      (should (= b 2))
+      (should (= c 3))
+      (should (= d 4))
+      (should (null e)))
+    (let (a b others)
+      (seq-setq (a b &rest others) seq)
+      (should (= a 1))
+      (should (= b 2))
+      (should (same-contents-p others (seq-drop seq 2)))))
+  (let ((a)
+        (seq '(1 (2 (3 (4))))))
+    (seq-setq (_ (_ (_ (a)))) seq)
+    (should (= a 4)))
+  (let (seq a b c)
+    (seq-setq (a b c) seq)
+    (should (null a))
+    (should (null b))
+    (should (null c))))
+
 (ert-deftest test-seq-min-max ()
   (with-test-sequences (seq '(4 5 3 2 0 4))
     (should (= (seq-min seq) 0))