Merge pull request #28 from shosti/master

Add -insert-at

README.md

@@ -39,6 +39,7 @@ Or you can just dump `dash.el` in your load path somewhere.
 * [-take-while](#-take-while-pred-list) `(pred list)`
 * [-drop-while](#-drop-while-pred-list) `(pred list)`
 * [-split-at](#-split-at-n-list) `(n list)`
+* [-insert-at](#-insert-at-n-x-list) `(n x list)`
 * [-split-with](#-split-with-pred-list) `(pred list)`
 * [-separate](#-separate-pred-list) `(pred list)`
 * [-partition](#-partition-n-list) `(n list)`
@@ -392,6 +393,15 @@ Returns a list of ((-take `n` `list`) (-drop `n` `list`)), in no more than one p
 (-split-at 17 '(1 2 3 4 5)) ;; => '((1 2 3 4 5) nil)
 ```
 
+### -insert-at `(n x list)`
+
+Returns a list with `x` inserted into `list` at position `n`.
+
+```cl
+(-insert-at 1 'x '(a b c)) ;; => '(a x b c)
+(-insert-at 12 'x '(a b c)) ;; => '(a b c x)
+```
+
 ### -split-with `(pred list)`
 
 Returns a list of ((-take-while `pred` `list`) (-drop-while `pred` `list`)), in no more than one pass through the list.

dash.el

@@ -411,6 +411,11 @@ FROM or TO may be negative."
         (!cdr list)))
     (list (nreverse result) list)))
 
+(defun -insert-at (n x list)
+  "Returns a list with X inserted into LIST at position N."
+  (let ((split-list (-split-at n list)))
+    (append (car split-list) (cons x (cadr split-list)))))
+
 (defmacro --split-with (pred list)
   "Anaphoric form of `-split-with'."
   (let ((l (make-symbol "list"))
@@ -843,6 +848,7 @@ Returns nil if N is less than 1."
                            "--drop-while"
                            "-drop-while"
                            "-split-at"
+                           "-insert-at"
                            "--split-with"
                            "-split-with"
                            "-partition"

dev/examples.el

@@ -150,6 +150,10 @@
   (-split-at 3 '(1 2 3 4 5)) => '((1 2 3) (4 5))
   (-split-at 17 '(1 2 3 4 5)) => '((1 2 3 4 5) nil))
 
+(defexamples -insert-at
+  (-insert-at 1 'x '(a b c)) => '(a x b c)
+  (-insert-at 12 'x '(a b c)) => '(a b c x))
+
 (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))