From ec6a85fcb588dc095f02a433499d3c3fec0d7367 Mon Sep 17 00:00:00 2001
From: Magnar Sveen <magnars@gmail.com>
Date: Sun, 21 Oct 2012 18:45:42 +0200
Subject: [PATCH] Add threading macro !!-> with `it` as placeholder.

---
 README.md   | 16 +++++++++++++++-
 bang.el     | 11 +++++++++++
 examples.el | 10 ++++++++--
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 8cbfadd..5441fd2 100644
--- a/README.md
+++ b/README.md
@@ -27,6 +27,7 @@ Or you can just dump `bang.el` in your load path somewhere.
 * [!rpartial](#rpartial-fn-rest-args) `(fn &rest args)`
 * [!->](#x-optional-form-rest-more) `(x &optional form &rest more)`
 * [!->>](#x-form-rest-more) `(x form &rest more)`
+* [!!->](#x-form-rest-more) `(x form &rest more)`
 * [!difference](#difference-list-list2) `(list list2)`
 * [!intersection](#intersection-list-list2) `(list list2)`
 * [!distinct](#distinct-list) `(list)`
@@ -179,8 +180,8 @@ through the `rep` function.
 
 ```cl
 (!replace-where 'even? 'square '(1 2 3 4)) ;; => '(1 4 3 16)
-(!replace-where (lambda (n) (= n 3)) (lambda (n) 0) '(1 2 3 4)) ;; => '(1 2 0 4)
 (!!replace-where (> it 2) (* it it) '(1 2 3 4)) ;; => '(1 2 9 16)
+(!!replace-where (= it 2) 17 '(1 2 3 4)) ;; => '(1 17 3 4)
 ```
 
 ### !first `(fn list)`
@@ -247,6 +248,19 @@ last item in second form, etc.
 (!->> 5 (- 8)) ;; => 3
 ```
 
+### !!-> `(x form &rest more)`
+
+Threads the expr through the forms. Inserts `x` at the position
+signified by the token `it` in the first form. If there are more
+forms, inserts the first form at the position signified by `it`
+in in second form, etc.
+
+```cl
+(!!-> "def" (concat "abc" it "ghi")) ;; => "abcdefghi"
+(!!-> "def" (concat "abc" it "ghi") (upcase it)) ;; => "ABCDEFGHI"
+(!!-> "def" (concat "abc" it "ghi") upcase) ;; => "ABCDEFGHI"
+```
+
 ### !difference `(list list2)`
 
 Return a new list with only the members of `list` that are not in `list2`.
diff --git a/bang.el b/bang.el
index 065662d..4f5c404 100644
--- a/bang.el
+++ b/bang.el
@@ -215,6 +215,17 @@ last item in second form, etc."
         (list form x))
     `(!->> (!->> ,x ,form) ,@more)))
 
+(defmacro !!-> (x form &rest more)
+  "Threads the expr through the forms. Inserts X at the position
+signified by the token `it' in the first form. If there are more
+forms, inserts the first form at the position signified by `it'
+in in second form, etc."
+  (if (null more)
+      (if (listp form)
+          (!!replace-where (eq it 'it) x form)
+        (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 6bfec6f..d894a4d 100644
--- a/examples.el
+++ b/examples.el
@@ -65,8 +65,9 @@
 
 (defexamples !replace-where
   (!replace-where 'even? 'square '(1 2 3 4)) => '(1 4 3 16)
-  (!replace-where (lambda (n) (= n 3)) (lambda (n) 0) '(1 2 3 4)) => '(1 2 0 4)
-  (!!replace-where (> it 2) (* it it) '(1 2 3 4)) => '(1 2 9 16))
+  (!!replace-where (> it 2) (* it it) '(1 2 3 4)) => '(1 2 9 16)
+  (!!replace-where (= it 2) 17 '(1 2 3 4)) => '(1 17 3 4)
+  (!replace-where (lambda (n) (= n 3)) (lambda (n) 0) '(1 2 3 4)) => '(1 2 0 4))
 
 (defexamples !first
   (!first 'even? '(1 2 3)) => 2
@@ -95,6 +96,11 @@
   (!->> 5 (- 8)) => 3
   (!->> 5 (- 3) square) => 4)
 
+(defexamples !!->
+  (!!-> "def" (concat "abc" it "ghi")) => "abcdefghi"
+  (!!-> "def" (concat "abc" it "ghi") (upcase it)) => "ABCDEFGHI"
+  (!!-> "def" (concat "abc" it "ghi") upcase) => "ABCDEFGHI")
+
 (defexamples !difference
   (!difference '() '()) => '()
   (!difference '(1 2 3) '(4 5 6)) => '(1 2 3)