add as-> macro

hy/core/macros.hy

@@ -30,6 +30,15 @@
         [hy.models.symbol [HySymbol]]
         [hy._compat [PY33 PY34]])
 
+(defmacro as-> [head name &rest rest]
+  "Becomes ordered assignments to the provided name. The previous result
+  is thus available in each form. Returns the final result, and leaves the name
+  bound to it in the local scope. This behaves like the threading macros, but
+  requires you to specify the threading point per form via the name."
+  `(do (setv
+         ~name ~head
+         ~@(interleave (repeat name) rest))
+     ~name))
 
 (defmacro with [args &rest body]
   "shorthand for nested with* loops: