Add -iteratefn

README.md

@@ -198,6 +198,7 @@ These combinators require Emacs 24 for its lexical scope. So they are offered in
 * [-not](#-not-pred) `(pred)`
 * [-orfn](#-orfn-rest-preds) `(&rest preds)`
 * [-andfn](#-andfn-rest-preds) `(&rest preds)`
+* [-iteratefn](#-iteratefn-fn-n) `(fn n)`
 
 ## Anaphoric functions
 
@@ -1665,6 +1666,27 @@ In types: [a -> Bool] -> a -> Bool
 (-filter (-andfn (-not 'even?) (-cut >= 5 <>)) '(1 2 3 4 5 6 7 8 9 10)) ;; => '(1 3 5)
 ```
 
+#### -iteratefn `(fn n)`
+
+Return a function `fn` composed `n` times with itself.
+
+`fn` is a unary function.  If you need to use a function of higher
+arity, use `-applify` first to turn it into an unary function.
+
+With n = 0, this acts as identity function.
+
+In types: (a -> a) -> Int -> a -> a.
+
+This function satisfies the following law:
+
+  (funcall (-iteratefn fn n) init) = (-last-item (-iterate fn init (1+ n))).
+
+```cl
+(funcall (-iteratefn (lambda (x) (* x x)) 3) 2) ;; => 256
+(funcall (-iteratefn '1+ 3) 1) ;; => 4
+(funcall (-iteratefn 'cdr 3) '(1 2 3 4 5)) ;; => '(4 5)
+```
+
 
 ## Contribute
 

dash-functional.el

@@ -60,7 +60,7 @@ each fn to the result of applying the previous fn to
 the arguments (right-to-left)."
   (lambda (&rest args)
     (car (-reduce-r-from (lambda (fn xs) (list (apply fn xs)))
-			 args fns))))
+                         args fns))))
 
 (defun -applify (fn)
   "Changes an n-arity function FN to a 1-arity function that
@@ -120,6 +120,21 @@ PREDS returns non-nil on x.
 In types: [a -> Bool] -> a -> Bool"
   (lambda (x) (-all? (-cut funcall <> x) preds)))
 
+(defun -iteratefn (fn n)
+  "Return a function FN composed N times with itself.
+
+FN is a unary function.  If you need to use a function of higher
+arity, use `-applify' first to turn it into an unary function.
+
+With n = 0, this acts as identity function.
+
+In types: (a -> a) -> Int -> a -> a.
+
+This function satisfies the following law:
+
+  (funcall (-iteratefn fn n) init) = (-last-item (-iterate fn init (1+ n)))."
+  (lambda (x) (--dotimes n (setq x (funcall fn x))) x))
+
 (provide 'dash-functional)
 
 ;;; dash-functional.el ends here

dev/examples.el

@@ -712,4 +712,17 @@
       (funcall (-andfn (-cut < <> 10) 'even?) 6) => t
       (funcall (-andfn (-cut < <> 10) 'even?) 12) => nil
       (-filter (-andfn (-not 'even?) (-cut >= 5 <>)) '(1 2 3 4 5 6 7 8 9 10)) => '(1 3 5))
+
+    (defexamples -iteratefn
+      (funcall (-iteratefn (lambda (x) (* x x)) 3) 2) => 256
+      (funcall (-iteratefn '1+ 3) 1) => 4
+      (funcall (-iteratefn 'cdr 3) '(1 2 3 4 5)) => '(4 5)
+      (let ((init '(1 2 3 4 5))
+            (fn 'cdr))
+        (and (equal (funcall (-iteratefn fn 0) init)
+                    (-last-item (-iterate fn init (1+ 0))))
+             (equal (funcall (-iteratefn fn 3) init)
+                    (-last-item (-iterate fn init (1+ 3))))
+             (equal (funcall (-iteratefn fn 5) init)
+                    (-last-item (-iterate fn init (1+ 5)))))))
     ))