Throw an error on unbalanced expressions

hy/lex/states.py

@@ -161,6 +161,9 @@ class ListeyThing(State):
         if char == self.end_char:
             return Idle
 
+        if char in ")]}":
+            raise LexException("Unexpected closing character: `%s'" % (char))
+
         if char in WHITESPACE:
             self.commit()
             return

tests/lex/test_lex.py

@@ -44,6 +44,21 @@ def test_lex_exception():
         pass
 
 
+def test_unbalanced_exception():
+    """Ensure the tokenization fails on unbalanced expressions"""
+    try:
+        tokenize("(bar))")
+        assert True is False
+    except LexException:
+        pass
+
+    try:
+        tokenize("(baz [quux]])")
+        assert True is False
+    except LexException:
+        pass
+
+
 def test_lex_expression_symbols():
     """ Make sure that expressions produce symbols """
     objs = tokenize("(foo bar)")