set the value of empty hy expression to []

hy/macros.py

@@ -70,7 +70,12 @@ _wrappers = {
 
 def process(tree, module_name):
     if isinstance(tree, HyExpression):
-        fn = tree[0]
+        try:
+            fn = tree[0]
+        except IndexError:
+            ntree = HyList()
+            ntree.replace(tree)
+            return ntree
         if fn in ("quote", "quasiquote"):
             return tree
         ntree = HyExpression(

tests/native_tests/language.hy

@@ -755,3 +755,7 @@
       (continue)) 
     (.append y x))
   (assert (= y [5])))
+
+(defn test-empty-list []
+  "Evaluate an empty list to a []"
+  (assert (= () [])))