Add -annotate

README.md

@@ -134,6 +134,7 @@ Operations dual to reductions, building lists from seed value rather than consum
 * [-interleave](#-interleave-rest-lists) `(&rest lists)`
 * [-zip-with](#-zip-with-fn-list1-list2) `(fn list1 list2)`
 * [-zip](#-zip-rest-lists) `(&rest lists)`
+* [-annotate](#-annotate-fn-list) `(fn list)`
 * [-first](#-first-pred-list) `(pred list)`
 * [-last](#-last-pred-list) `(pred list)`
 * [-first-item](#-first-item-list) `(list)`
@@ -1103,6 +1104,17 @@ of cons cells. Otherwise, return the groupings as a list of lists.
 (-zip '(1 2 3 4) '(4 5 6)) ;; => '((1 . 4) (2 . 5) (3 . 6))
 ```
 
+#### -annotate `(fn list)`
+
+Returns a list of cons cells where each cell is `fn` applied to each
+element of `list` paired with the unmodified element of `list`.
+
+```cl
+(-annotate '1+ '(1 2 3)) ;; => '((2 . 1) (3 . 2) (4 . 3))
+(-annotate 'length '(("h" "e" "l" "l" "o") ("hello" "world"))) ;; => '((5 "h" "e" "l" "l" "o") (2 "hello" "world"))
+(--annotate (< 1 it) '(0 1 2 3)) ;; => '((nil . 0) (nil . 1) (t . 2) (t . 3))
+```
+
 #### -first `(pred list)`
 
 Returns the first x in `list` where (`pred` x) is non-nil, else nil.
@@ -1669,7 +1681,7 @@ Change `readme-template.md` or `examples-to-docs.el` instead.
  - [Emanuel Evans](https://github.com/shosti) contributed `-if-let`, `-when-let` and `-insert-at`.
  - [Johan Andersson](https://github.com/rejeep) contributed `-sum`, `-product` and `-same-items?`
  - [Christina Whyte](https://github.com/kurisuwhyte) contributed `-compose`
- - [Steve Lamb](https://github.com/steventlamb) contributed an n-ary version of `-zip`
+ - [Steve Lamb](https://github.com/steventlamb) contributed `-annotate` and an n-ary version of `-zip`
 
 Thanks!
 

dash.el

@@ -818,6 +818,16 @@ of cons cells. Otherwise, return the groupings as a list of lists. "
         (--map (cons (car it) (cadr it)) results)
       results)))
 
+(defun -annotate (fn list)
+  "Returns a list of cons cells where each cell is FN applied to each
+element of LIST paired with the unmodified element of LIST."
+  (-zip (-map fn list) list))
+
+(defmacro --annotate (form list)
+  "Anaphoric version of `-annotate'."
+  (declare (debug (form form)))
+  `(-annotate (lambda (it) ,form) ,list))
+
 (defun -partial (fn &rest args)
   "Takes a function FN and fewer than the normal arguments to FN,
 and returns a fn that takes a variable number of additional ARGS.

dev/examples.el

@@ -439,6 +439,11 @@
     (-zip '(1 2 3) '(4 5 6) '(7 8 9)) => '((1 4 7) (2 5 8) (3 6 9))
     (-zip '(1 2) '(3 4 5) '(6)) => '((1 3 6)))
 
+  (defexamples -annotate
+    (-annotate '1+ '(1 2 3)) => '((2 . 1) (3 . 2) (4 . 3))
+    (-annotate 'length '(("h" "e" "l" "l" "o") ("hello" "world"))) => '((5 . ("h" "e" "l" "l" "o")) (2 . ("hello" "world")))
+    (--annotate (< 1 it) '(0 1 2 3)) => '((nil . 0) (nil . 1) (t . 2) (t . 3)))
+
   (defexamples -first
     (-first 'even? '(1 2 3)) => 2
     (-first 'even? '(1 3 5)) => nil

readme-template.md

@@ -174,7 +174,7 @@ Change `readme-template.md` or `examples-to-docs.el` instead.
  - [Emanuel Evans](https://github.com/shosti) contributed `-if-let`, `-when-let` and `-insert-at`.
  - [Johan Andersson](https://github.com/rejeep) contributed `-sum`, `-product` and `-same-items?`
  - [Christina Whyte](https://github.com/kurisuwhyte) contributed `-compose`
- - [Steve Lamb](https://github.com/steventlamb) contributed an n-ary version of `-zip`
+ - [Steve Lamb](https://github.com/steventlamb) contributed `-annotate` and an n-ary version of `-zip`
 
 Thanks!