Add -interleave

README.md

@@ -28,6 +28,7 @@ Or you can just dump `dash.el` in your load path somewhere.
 * [-split-at](#split-at-n-list) `(n list)`
 * [-split-with](#split-with-fn-list) `(fn list)`
 * [-interpose](#interpose-sep-list) `(sep list)`
+* [-interleave](#interleave-rest-lists) `(&rest lists)`
 * [-replace-where](#replace-where-pred-rep-list) `(pred rep list)`
 * [-first](#first-fn-list) `(fn list)`
 * [-difference](#difference-list-list2) `(list list2)`
@@ -244,6 +245,16 @@ Returns a new list of all elements in `list` separated by `sep`.
 (-interpose "-" '("a" "b" "c")) ;; => '("a" "-" "b" "-" "c")
 ```
 
+### -interleave `(&rest lists)`
+
+Returns a new list of the first item in each list, then the second etc.
+
+```cl
+(-interleave '(1 2) '("a" "b")) ;; => '(1 "a" 2 "b")
+(-interleave '(1 2) '("a" "b") '("A" "B")) ;; => '(1 "a" "A" 2 "b" "B")
+(-interleave '(1 2 3) '("a" "b")) ;; => '(1 "a" 2 "b")
+```
+
 ### -replace-where `(pred rep list)`
 
 Returns a new list where the elements in `list` that does not match the `pred` function

dash.el

@@ -217,6 +217,14 @@ Thus function FN should return a collection."
       (setq list (cdr list)))
     (nreverse result)))
 
+(defun -interleave (&rest lists)
+  "Returns a new list of the first item in each list, then the second etc."
+  (let (result)
+    (while (--all? (not (null it)) lists)
+      (--each lists (setq result (cons (car it) result)))
+      (setq lists (-map 'cdr lists)))
+    (nreverse result)))
+
 (defmacro --replace-where (pred rep list)
   "Anaphoric form of `-replace-where'."
   (let ((l (make-symbol "list"))

examples.el

@@ -94,6 +94,12 @@
   (-interpose "-" '("a")) => '("a")
   (-interpose "-" '("a" "b" "c")) => '("a" "-" "b" "-" "c"))
 
+(defexamples -interleave
+  (-interleave '(1 2) '("a" "b")) => '(1 "a" 2 "b")
+  (-interleave '(1 2) '("a" "b") '("A" "B")) => '(1 "a" "A" 2 "b" "B")
+  (-interleave '(1 2 3) '("a" "b")) => '(1 "a" 2 "b")
+  (-interleave '(1 2 3) '("a" "b" "c" "d")) => '(1 "a" 2 "b" 3 "c"))
+
 (defexamples -replace-where
   (-replace-where 'even? 'square '(1 2 3 4)) => '(1 4 3 16)
   (--replace-where (> it 2) (* it it) '(1 2 3 4)) => '(1 2 9 16)