Add !split-with

README.md

@@ -22,6 +22,7 @@ Or you can just dump `bang.el` in your load path somewhere.
 * [!mapcat](#mapcat-fn-list) `(fn list)`
 * [!take-while](#take-while-fn-list) `(fn list)`
 * [!drop-while](#drop-while-fn-list) `(fn list)`
+* [!split-with](#split-with-fn-list) `(fn list)`
 * [!interpose](#interpose-sep-list) `(sep list)`
 * [!replace-where](#replace-where-pred-rep-list) `(pred rep list)`
 * [!first](#first-fn-list) `(fn list)`
@@ -184,6 +185,16 @@ Returns the tail of `list` starting from the first item for which (`fn` item) re
 (!!drop-while (< it 4) '(1 2 3 4 3 2 1)) ;; => '(4 3 2 1)
 ```
 
+### !split-with `(fn list)`
+
+Returns a list of ((!take-while `fn` `list`) (!drop-while `fn` `list`))
+
+```cl
+(!split-with 'even? '(1 2 3 4)) ;; => '(nil (1 2 3 4))
+(!split-with 'even? '(2 4 5 6)) ;; => '((2 4) (5 6))
+(!!split-with (< it 4) '(1 2 3 4 3 2 1)) ;; => '((1 2 3) (4 3 2 1))
+```
+
 ### !interpose `(sep list)`
 
 Returns a new list of all elements in `list` separated by `sep`.

bang.el

@@ -171,6 +171,15 @@ Thus function FN should return a collection."
   "Returns the tail of LIST starting from the first item for which (FN item) returns nil."
   (!!drop-while (funcall fn it) list))
 
+(defmacro !!split-with (form list)
+  "Anaphoric form of `!split-with'."
+  `(list (!!take-while ,form ,list)
+         (!!drop-while ,form ,list)))
+
+(defun !split-with (fn list)
+  "Returns a list of ((!take-while FN LIST) (!drop-while FN LIST))"
+  (!!split-with (funcall fn it) list))
+
 (defun !interpose (sep list)
   "Returns a new list of all elements in LIST separated by SEP."
   (let (result)

examples.el

@@ -68,6 +68,11 @@
   (!drop-while 'even? '(2 4 5 6)) => '(5 6)
   (!!drop-while (< it 4) '(1 2 3 4 3 2 1)) => '(4 3 2 1))
 
+(defexamples !split-with
+  (!split-with 'even? '(1 2 3 4)) => '(() (1 2 3 4))
+  (!split-with 'even? '(2 4 5 6)) => '((2 4) (5 6))
+  (!!split-with (< it 4) '(1 2 3 4 3 2 1)) => '((1 2 3) (4 3 2 1)))
+
 (defexamples !interpose
   (!interpose "-" '()) => '()
   (!interpose "-" '("a")) => '("a")