Simplify -non-nil

* dash.el (-non-nil): Use --filter for speed.
* dev/examples.el (-non-nil): Extend tests.

* README.md:
* dash.texi: Regenerate docs.

README.md

@@ -586,10 +586,12 @@ The comparison is done with `equal`.
 
 #### -non-nil `(list)`
 
-Return all non-nil elements of `list`.
+Return a copy of `list` with all nil items removed.
 
 ```el
-(-non-nil '(1 nil 2 nil nil 3 4 nil 5 nil)) ;; => '(1 2 3 4 5)
+(-non-nil '(nil 1 nil 2 nil nil 3 4 nil 5 nil)) ;; => '(1 2 3 4 5)
+(-non-nil '((nil))) ;; => '((nil))
+(-non-nil '()) ;; => '()
 ```
 
 #### -slice `(list from &optional to step)`

dash.el

@@ -530,9 +530,9 @@ If you want to select the original items satisfying a predicate use `-filter'."
   (--keep (funcall fn it) list))
 
 (defun -non-nil (list)
-  "Return all non-nil elements of LIST."
+  "Return a copy of LIST with all nil items removed."
   (declare (pure t) (side-effect-free t))
-  (-remove 'null list))
+  (--filter it list))
 
 (defmacro --map-indexed (form list)
   "Anaphoric form of `-map-indexed'."

dash.texi

@@ -603,13 +603,21 @@ The comparison is done with @code{equal}.
 
 @anchor{-non-nil}
 @defun -non-nil (list)
-Return all non-nil elements of @var{list}.
+Return a copy of @var{list} with all nil items removed.
 
 @example
 @group
-(-non-nil '(1 nil 2 nil nil 3 4 nil 5 nil))
+(-non-nil '(nil 1 nil 2 nil nil 3 4 nil 5 nil))
     @result{} '(1 2 3 4 5)
 @end group
+@group
+(-non-nil '((nil)))
+    @result{} '((nil))
+@end group
+@group
+(-non-nil '())
+    @result{} '()
+@end group
 @end example
 @end defun
 

dev/examples.el

@@ -209,7 +209,12 @@ new list."
     (let ((l (list 1 2))) (setcar (-remove-item 2 l) 0) l) => '(1 2))
 
   (defexamples -non-nil
-    (-non-nil '(1 nil 2 nil nil 3 4 nil 5 nil)) => '(1 2 3 4 5))
+    (-non-nil '(nil 1 nil 2 nil nil 3 4 nil 5 nil)) => '(1 2 3 4 5)
+    (-non-nil '((()))) => '((()))
+    (-non-nil '()) => '()
+    (let ((l (list 1 2))) (setcar (-non-nil l) 0) l) => '(1 2)
+    (let ((l (list nil 1))) (setcar (-non-nil l) 0) l) => '(nil 1)
+    (let ((l (list 1 nil))) (setcar (-non-nil l) 0) l) => '(1 nil))
 
   (defexamples -slice
     (-slice '(1 2 3 4 5) 1) => '(2 3 4 5)