From 244bb4ac72afb682c52e48a1308b569ce782174d Mon Sep 17 00:00:00 2001
From: Damien Cassou <damien@cassou.me>
Date: Sat, 3 Sep 2022 18:47:04 +0200
Subject: [PATCH] Add new function `seq-remove-at-position'

* doc/lispref/sequences.texi (Sequence Functions): Document it.

* lisp/emacs-lisp/seq.el (seq-remove-at-position): New function.

* lisp/emacs-lisp/shortdoc.el (sequence): Mention it.

* test/lisp/emacs-lisp/seq-tests.el (test-seq-remove-at-position):
Test it.
---
 doc/lispref/sequences.texi        | 18 ++++++++++++++++++
 etc/NEWS                          |  5 +++++
 lisp/emacs-lisp/seq.el            | 14 ++++++++++++++
 lisp/emacs-lisp/shortdoc.el       |  3 +++
 test/lisp/emacs-lisp/seq-tests.el |  8 ++++++++
 5 files changed, 48 insertions(+)

diff --git a/doc/lispref/sequences.texi b/doc/lispref/sequences.texi
index 1f6f80521c..e90502df3c 100644
--- a/doc/lispref/sequences.texi
+++ b/doc/lispref/sequences.texi
@@ -680,6 +680,24 @@ Sequence Functions
 @end example
 @end defun
 
+@defun seq-remove-at-position sequence n
+@cindex removing from sequences
+  This function returns a copy of @var{sequence} where the element at
+  (zero-based) index @var{n} got removed. The result is a sequence of
+  the same type as @var{sequence}.
+
+@example
+@group
+(seq-remove-at-position [1 -1 3 -3 5] 0)
+@result{} [-1 3 -3 5]
+@end group
+@group
+(seq-remove-at-position [1 -1 3 -3 5] 3)
+@result{} [1 -1 3 5]
+@end group
+@end example
+@end defun
+
 @defun seq-reduce function sequence initial-value
 @cindex reducing sequences
   This function returns the result of calling @var{function} with
diff --git a/etc/NEWS b/etc/NEWS
index cc4714e71c..2fdc63551f 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2734,6 +2734,11 @@ The default timeout value can be defined by the new variable
 ** New function 'seq-split'.
 This returns a list of sub-sequences of the specified sequence.
 
++++
+** New function 'seq-remove-at-position'.
+This function returns a copy of the specified sequence where the
+element at a given (zero-based) index got removed.
+
 +++
 ** 'plist-get', 'plist-put' and 'plist-member' are no longer limited to 'eq'.
 These function now take an optional comparison predicate argument.
diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
index b6f0f66e5b..4d05f2c589 100644
--- a/lisp/emacs-lisp/seq.el
+++ b/lisp/emacs-lisp/seq.el
@@ -346,6 +346,20 @@ seq-remove
   (seq-filter (lambda (elt) (not (funcall pred elt)))
               sequence))
 
+;;;###autoload
+(cl-defgeneric seq-remove-at-position (sequence n)
+  "Return a copy of SEQUENCE where the element at N got removed.
+
+N is the (zero-based) index of the element that should not be in
+the result.
+
+The result is a sequence of the same type as SEQUENCE."
+  (seq-concatenate
+   (let ((type (type-of sequence)))
+     (if (eq type 'cons) 'list type))
+   (seq-subseq sequence 0 n)
+   (seq-subseq sequence (1+ n))))
+
 ;;;###autoload
 (cl-defgeneric seq-reduce (function sequence initial-value)
   "Reduce the function FUNCTION across SEQUENCE, starting with INITIAL-VALUE.
diff --git a/lisp/emacs-lisp/shortdoc.el b/lisp/emacs-lisp/shortdoc.el
index 990dabe351..6a366ec0fc 100644
--- a/lisp/emacs-lisp/shortdoc.el
+++ b/lisp/emacs-lisp/shortdoc.el
@@ -888,6 +888,9 @@ sequence
    :eval (seq-filter #'numberp '(a b 3 4 f 6)))
   (seq-remove
    :eval (seq-remove #'numberp '(1 2 c d 5)))
+  (seq-remove-at-position
+   :eval (seq-remove-at-position '(a b c d e) 3)
+   :eval (seq-remove-at-position [a b c d e] 0))
   (seq-group-by
    :eval (seq-group-by #'cl-plusp '(-1 2 3 -4 -5 6)))
   (seq-union
diff --git a/test/lisp/emacs-lisp/seq-tests.el b/test/lisp/emacs-lisp/seq-tests.el
index 1a27467d29..6249e48617 100644
--- a/test/lisp/emacs-lisp/seq-tests.el
+++ b/test/lisp/emacs-lisp/seq-tests.el
@@ -137,6 +137,14 @@ test-seq-remove
   (with-test-sequences (seq '())
     (should (equal (seq-remove #'test-sequences-evenp seq) '()))))
 
+(ert-deftest test-seq-remove-at-position ()
+  (with-test-sequences (seq '(1 2 3 4))
+    (should (same-contents-p (seq-remove-at-position seq 2) '(1 2 4)))
+    (should (same-contents-p (seq-remove-at-position seq 0) '(2 3 4)))
+    (should (same-contents-p (seq-remove-at-position seq 3) '(1 2 3)))
+    (should (eq (type-of (seq-remove-at-position seq 2))
+                (type-of seq)))))
+
 (ert-deftest test-seq-count ()
   (with-test-sequences (seq '(6 7 8 9 10))
     (should (equal (seq-count #'test-sequences-evenp seq) 3))
-- 
2.36.2