Merge pull request #1657 from Kodiologist/no-empty-exprs

Make empty expressions illegal at the top level

NEWS.rst

@@ -1,5 +1,12 @@
 .. default-role:: code
 
+Unreleased
+==============================
+
+Removals
+------------------------------
+* Empty expressions (`()`) are no longer legal at the top level.
+
 0.15.0
 ==============================
 

hy/compiler.py

@@ -1546,8 +1546,9 @@ class HyASTCompiler(object):
             # Go through compile again if the type changed.
             return self.compile(expression)
 
-        if expression == []:
+        if not expression:
-            return self.compile_atom(HyList().replace(expression))
+            raise HyTypeError(
+                expression, "empty expressions are not allowed at top level")
 
         fn = expression[0]
         func = None

tests/compilers/test_ast.py

@@ -67,6 +67,12 @@ def test_ast_bad_type():
         pass
 
 
+def test_empty_expr():
+    "Empty expressions should be illegal at the top level."
+    cant_compile("(print ())")
+    can_compile("(print '())")
+
+
 def test_ast_bad_if():
     "Make sure AST can't compile invalid if*"
     cant_compile("(if*)")

tests/native_tests/language.hy

@@ -1401,11 +1401,6 @@
   (assert (= y [5])))
 
 
-(defn test-empty-list []
-  "Evaluate an empty list to a []"
-  (assert (= () [])))
-
-
 (defn test-string []
   (assert (string? (string "a")))
   (assert (string? (string 1)))