Improve the semantic of seq-some

Update seq-some to return non-nil if the predicate returns non-nil for
any element of the seq, in which case the returned value is the one
returned by the predicate.

* lisp/emacs-lisp/seq.el (seq-some): Update the function and its
  docstring.
* test/automated/seq-tests.el (test-seq-some): Add a regression test.
* doc/lispref/sequences.texi (Sequence Functions): Update the
  documentation for seq-some.

doc/lispref/sequences.texi

@@ -558,18 +558,23 @@ calling @var{function}.
 @end defun
 
 @defun seq-some predicate sequence
-  This function returns the first member of sequence for which @var{predicate}
-returns non-@code{nil}.
+  This function returns non-@code{nil} if @var{predicate} returns
+non-@code{nil} for any element of @var{sequence}.  If so, the returned
+value is the value returned by @var{predicate}.
 
 @example
 @group
 (seq-some #'numberp ["abc" 1 nil])
-@result{} 1
+@result{} t
 @end group
 @group
 (seq-some #'numberp ["abc" "def"])
 @result{} nil
 @end group
+@group
+(seq-some #'null ["abc" 1 nil])
+@result{} t
+@end group
 @end example
 @end defun
 

lisp/emacs-lisp/seq.el

@@ -261,11 +261,13 @@ If SEQ is empty, return INITIAL-VALUE and FUNCTION is not called."
     t))
 
 (cl-defgeneric seq-some (pred seq)
-  "Return any element for which (PRED element) is non-nil in SEQ, nil otherwise."
+  "Return non-nil if (PRED element) is non-nil for any element in SEQ, nil otherwise.
+If so, return the non-nil value returned by PRED."
   (catch 'seq--break
     (seq-doseq (elt seq)
-      (when (funcall pred elt)
-        (throw 'seq--break elt)))
+      (let ((result (funcall pred elt)))
+        (when result
+          (throw 'seq--break result))))
     nil))
 
 (cl-defgeneric seq-count (pred seq)
@@ -280,8 +282,8 @@ If SEQ is empty, return INITIAL-VALUE and FUNCTION is not called."
   "Return the first element in SEQ that equals to ELT.
 Equality is defined by TESTFN if non-nil or by `equal' if nil."
   (seq-some (lambda (e)
-                (funcall (or testfn #'equal) elt e))
-              seq))
+              (funcall (or testfn #'equal) elt e))
+            seq))
 
 (cl-defgeneric seq-uniq (seq &optional testfn)
   "Return a list of the elements of SEQ with duplicates removed.

test/automated/seq-tests.el

@@ -131,11 +131,12 @@ Evaluate BODY for each created sequence.
 
 (ert-deftest test-seq-some ()
   (with-test-sequences (seq '(4 3 2 1))
-    (should (= (seq-some #'test-sequences-evenp seq) 4))
-    (should (= (seq-some #'test-sequences-oddp seq) 3))
+    (should (seq-some #'test-sequences-evenp seq))
+    (should (seq-some #'test-sequences-oddp seq))
     (should-not (seq-some (lambda (elt) (> elt 10)) seq)))
   (with-test-sequences (seq '())
-    (should-not (seq-some #'test-sequences-oddp seq))))
+    (should-not (seq-some #'test-sequences-oddp seq)))
+  (should (seq-some #'null '(1 nil 2))))
 
 (ert-deftest test-seq-contains ()
   (with-test-sequences (seq '(3 4 5 6))