Add -each-while

README.md

@@ -25,6 +25,7 @@ Or you can just dump `dash.el` in your load path somewhere.
 * [-all?](#-all-fn-list) `(fn list)`
 * [-none?](#-none-fn-list) `(fn list)`
 * [-each](#-each-list-fn) `(list fn)`
+* [-each-while](#-each-while-list-pred-fn) `(list pred fn)`
 * [-take](#-take-n-list) `(n list)`
 * [-drop](#-drop-n-list) `(n list)`
 * [-take-while](#-take-while-fn-list) `(fn list)`
@@ -227,6 +228,16 @@ Calls `fn` with every item in `list`. Returns nil, used for side-effects only.
 (let (s) (--each '(1 2 3) (setq s (cons it s))) s) ;; => '(3 2 1)
 ```
 
+### -each-while `(list pred fn)`
+
+Calls `fn` with every item in `list` while (`pred` item) is non-nil.
+Returns nil, used for side-effects only.
+
+```cl
+(let (s) (-each-while '(2 4 5 6) 'even? (lambda (item) (!cons item s))) s) ;; => '(4 2)
+(let (s) (--each-while '(1 2 3 4) (< it 3) (!cons it s)) s) ;; => '(2 1)
+```
+
 ### -take `(n list)`
 
 Returns a new list of the first `n` items in `list`, or all items if there are fewer than `n`.

dash.el

@@ -48,6 +48,22 @@
   "Calls FN with every item in LIST. Returns nil, used for side-effects only."
   (--each list (funcall fn it)))
 
+(defmacro --each-while (list pred form)
+  "Anaphoric form of `-each-while'."
+  (let ((l (make-symbol "list"))
+        (c (make-symbol "continue")))
+    `(let ((,l ,list)
+           (,c t))
+       (while (and ,l ,c)
+         (let ((it (car ,l)))
+           (if ,pred ,form (setq ,c nil)))
+         (!cdr ,l)))))
+
+(defun -each-while (list pred fn)
+  "Calls FN with every item in LIST while (PRED item) is non-nil.
+Returns nil, used for side-effects only."
+  (--each-while list (funcall pred it) (funcall fn it)))
+
 (defun -map (fn list)
   "Returns a new list consisting of the result of applying FN to the items in LIST."
   (mapcar fn list))

examples.el

@@ -83,6 +83,10 @@
   (let (s) (--each '(1 2 3) (setq s (cons it s))) s) => '(3 2 1)
   (let (s) (--each (reverse (three-letters)) (setq s (cons it s))) s) => '("A" "B" "C"))
 
+(defexamples -each-while
+  (let (s) (-each-while '(2 4 5 6) 'even? (lambda (item) (!cons item s))) s) => '(4 2)
+  (let (s) (--each-while '(1 2 3 4) (< it 3) (!cons it s)) s) => '(2 1))
+
 (defexamples -take
   (-take 3 '(1 2 3 4 5)) => '(1 2 3)
   (-take 17 '(1 2 3 4 5)) => '(1 2 3 4 5))