Add -splice and -splice-list

README.md

@@ -44,6 +44,8 @@ Include this in your emacs settings to get syntax highlighting:
 * [-map-when](#-map-when-pred-rep-list) `(pred rep list)`
 * [-replace](#-replace-old-new-list) `(old new list)`
 * [-map-indexed](#-map-indexed-fn-list) `(fn list)`
+* [-splice](#-splice-pred-fun-list) `(pred fun list)`
+* [-splice-list](#-splice-list-pred-new-list-list) `(pred new-list list)`
 * [-flatten](#-flatten-l) `(l)`
 * [-flatten-n](#-flatten-n-num-list) `(num list)`
 * [-concat](#-concat-rest-lists) `(&rest lists)`
@@ -309,6 +311,33 @@ In the anaphoric form `--map-indexed`, the index is exposed as `it-index`.
 (--map-indexed (- it it-index) '(1 2 3 4)) ;; => '(1 1 1 1)
 ```
 
+#### -splice `(pred fun list)`
+
+Splice lists generated by `fun` in place of elements matching `pred` in `list`.
+
+`fun` takes the element matching `pred` as input.
+
+This function can be used as replacement for `,@` in case you
+need to splice several lists at marked positions (for example
+with keywords).
+
+```cl
+(-splice 'even? (lambda (x) (list x x)) '(1 2 3 4)) ;; => '(1 2 2 3 4 4)
+(--splice 't (list it it) '(1 2 3 4)) ;; => '(1 1 2 2 3 3 4 4)
+(--splice (equal it :magic) '((list of) (magical) (code)) '((foo) (bar) :magic (baz))) ;; => '((foo) (bar) (list of) (magical) (code) (baz))
+```
+
+#### -splice-list `(pred new-list list)`
+
+Splice `new-list` in place of elements matching `pred` in `list`.
+
+See also more general version: `-splice`.
+
+```cl
+(-splice-list 'keywordp '(a b c) '(1 :foo 2)) ;; => '(1 a b c 2)
+(-splice-list 'keywordp nil '(1 :foo 2)) ;; => '(1 2)
+```
+
 #### -flatten `(l)`
 
 Takes a nested list `l` and returns its contents as a single, flat list.

dash.el

@@ -301,6 +301,36 @@ Elements are compared using `equal'."
 Thus function FN should return a list."
   (--mapcat (funcall fn it) list))
 
+(defun -splice (pred fun list)
+  "Splice lists generated by FUN in place of elements matching PRED in LIST.
+
+FUN takes the element matching PRED as input.
+
+This function can be used as replacement for `,@' in case you
+need to splice several lists at marked positions (for example
+with keywords)."
+  (let (r)
+    (--each list
+      (if (funcall pred it)
+          (let ((new (funcall fun it)))
+            (--each new (!cons it r)))
+        (!cons it r)))
+    (nreverse r)))
+
+(defmacro --splice (pred form list)
+  "Anaphoric form of `-splice'."
+  `(-splice (lambda (it) ,pred) (lambda (it) ,form) ,list))
+
+(defun -splice-list (pred new-list list)
+  "Splice NEW-LIST in place of elements matching PRED in LIST.
+
+See also more general version: `-splice'."
+  (-splice pred (lambda (_) new-list) list))
+
+(defun --splice-list (pred new-list list)
+  "Anaphoric form of `-splice-list'."
+  `(-splice-list (lambda (it) ,pred) ,new-list ,list))
+
 (defun -cons* (&rest args)
   "Makes a new list from the elements of ARGS.
 
@@ -1471,6 +1501,10 @@ structure such as plist or alist."
                              "--keep"
                              "-map-indexed"
                              "--map-indexed"
+                             "-splice"
+                             "--splice"
+                             "-splice-list"
+                             "--splice-list"
                              "-map-when"
                              "--map-when"
                              "-replace-where"

dev/examples.el

@@ -48,6 +48,15 @@
     (-map-indexed (lambda (index item) (- item index)) '(1 2 3 4)) => '(1 1 1 1)
     (--map-indexed (- it it-index) '(1 2 3 4)) => '(1 1 1 1))
 
+  (defexamples -splice
+    (-splice 'even? (lambda (x) (list x x)) '(1 2 3 4)) => '(1 2 2 3 4 4)
+    (--splice 't (list it it) '(1 2 3 4)) => '(1 1 2 2 3 3 4 4)
+    (--splice (equal it :magic) '((list of) (magical) (code)) '((foo) (bar) :magic (baz))) => '((foo) (bar) (list of) (magical) (code) (baz)))
+
+  (defexamples -splice-list
+    (-splice-list 'keywordp '(a b c) '(1 :foo 2)) => '(1 a b c 2)
+    (-splice-list 'keywordp nil '(1 :foo 2)) => '(1 2))
+
   (defexamples -flatten
     (-flatten '((1))) => '(1)
     (-flatten '((1 (2 3) (((4 (5))))))) => '(1 2 3 4 5)