Adding in a Threading macro (->)

hy/core/bootstrap.py

@@ -45,3 +45,15 @@ def cond_macro(tree):
         ret = n
 
     return root
+
+
+@macro("_>")
+def threading_macro(tree):
+    tree.pop(0)  # ->
+    tree.reverse()
+    ret = tree.pop(0)
+    root = ret
+    for node in tree:
+        ret.insert(1, node)
+        ret = node
+    return root

tests/native_tests/language.hy

@@ -131,3 +131,8 @@
   (def foo "3")
   (assert (= *foo* FOO))
   (assert (!= *foo* foo)))
+
+(defn test-threading []
+  "NATIVE: test threading macro"
+  (assert (= (-> (.upper "a b c d") (.replace "A" "X") (.split))
+             ["X" "B" "C" "D"])))