Add seq-intersection and seq-difference to the seq library

* lisp/emacs-lisp/seq.el (seq-intersection, seq-difference): New
functions.

* test/automated/seq-tests.el: Add tests for seq-intersection and
seq-difference.

* doc/lispref/sequences.texi: Add documentation for seq-intersection
and seq-difference.

1 files changed, 29 insertions, 1 deletions

diff --git a/doc/lispref/sequences.texi b/doc/lispref/sequences.texi
index 1af353590cf..334b3478cb6 100644
--- a/doc/lispref/sequences.texi
+++ b/doc/lispref/sequences.texi
@@ -723,6 +723,35 @@ contain less elements than @var{n}.  @var{n} must be an integer.  If
 @end example
 @end defun
 
+@defun seq-intersection sequence1 sequence2 &optional function
+  This function returns a list of the elements that appear both in
+@var{sequence1} and @var{sequence2}.  If the optional argument
+@var{function} is non-@code{nil}, it is a function of two arguments to
+use to compare elements instead of the default @code{equal}.
+
+@example
+@group
+(seq-intersection [2 3 4 5] [1 3 5 6 7])
+@result {} (3 5)
+@end group
+@end example
+@end defun
+
+
+@defun seq-difference sequence1 sequence2 &optional function
+  This function returns a list of the elements that appear in
+@var{sequence1} but not in @var{sequence2}.  If the optional argument
+@var{function} is non-@code{nil}, it is a function of two arguments to
+use to compare elements instead of the default @code{equal}.
+
+@example
+@group
+(seq-difference '(2 3 4 5) [1 3 5 6 7])
+@result {} (2 4)
+@end group
+@end example
+@end defun
+
 @defun seq-group-by function sequence
   This function separates the elements of @var{sequence} into an alist
 whose keys are the result of applying @var{function} to each element
@@ -761,7 +790,6 @@ of type @var{type}.  @var{type} can be one of the following symbols:
 @end example
 @end defun
 
-
 @defmac seq-doseq (var sequence [result]) body@dots{}
 @cindex sequence iteration
   This macro is like @code{dolist}, except that @var{sequence} can be a list,