From 4205e58d7ea98096d2e7ca7e2a7ff750da66f514 Mon Sep 17 00:00:00 2001
From: Magnar Sveen <magnars@gmail.com>
Date: Sat, 20 Oct 2012 09:55:25 +0200
Subject: [PATCH] Add clojure threading macros, !-> and !->>

---
 bang.el     | 23 +++++++++++++++++++++++
 examples.el | 13 +++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/bang.el b/bang.el
index b8879c1..81c2350 100644
--- a/bang.el
+++ b/bang.el
@@ -154,6 +154,29 @@ args first and then ARGS."
   `(closure (t) (&rest args)
             (apply ',fn (append args ',args))))
 
+(defmacro !-> (x &optional form &rest more)
+  "Threads the expr through the forms. Inserts X as the second
+item in the first form, making a list of it if it is not a list
+already. If there are more forms, inserts the first form as the
+second item in second form, etc."
+  (cond
+   ((null form) x)
+   ((null more) (if (listp form)
+                    `(,(car form) ,x ,@(cdr form))
+                  (list form x)))
+   (:else `(!-> (!-> ,x ,form) ,@more))))
+
+(defmacro !->> (x form &rest more)
+  "Threads the expr through the forms. Inserts X as the last item
+in the first form, making a list of it if it is not a list
+already. If there are more forms, inserts the first form as the
+last item in second form, etc."
+  (if (null more)
+      (if (listp form)
+          `(,(car form) ,@(cdr form) ,x)
+        (list form x))
+    `(!->> (!->> ,x ,form) ,@more)))
+
 (defun !distinct (list)
   "Return a new list with all duplicates removed.
 The test for equality is done with `equal',
diff --git a/examples.el b/examples.el
index a57af86..2fcd990 100644
--- a/examples.el
+++ b/examples.el
@@ -71,6 +71,19 @@
   (funcall (!rpartial '- 5) 8) => 3
   (funcall (!rpartial '- 5 2) 10) => 3)
 
+(defexamples !->
+  (!-> "Abc") => "Abc"
+  (!-> "Abc" (concat "def")) => "Abcdef"
+  (!-> "Abc" (concat "def") (concat "ghi")) => "Abcdefghi"
+  (!-> 5 square) => 25
+  (!-> 5 (+ 3) square) => 64)
+
+(defexamples !->>
+  (!->> "Abc" (concat "def")) => "defAbc"
+  (!->> "Abc" (concat "def") (concat "ghi")) => "ghidefAbc"
+  (!->> 5 (- 8)) => 3
+  (!->> 5 (- 3) square) => 4)
+
 (defexamples !difference
   (!difference '() '()) => '()
   (!difference '(1 2 3) '(4 5 6)) => '(1 2 3)