Return error codes correctly (see #1)

def_main.py

@@ -10,7 +10,9 @@ def def_main(f: Callable) -> Callable:
     MAINS.append((f, s.filename, s.lineno))
 
     if f.__module__ == '__main__':
-        f(*sys.argv[1:])
+        result = f(*sys.argv[1:])
+        if result:
+            sys.exit(result)
 
     return f
 

test_main.py

@@ -2,5 +2,17 @@
 
 
 @def_main
-def main(*argv):
-    print('test_main says hello!, to', *argv)
+def main(message='you!', *rest):
+    print('test_main says hello!, to', message, *rest)
+
+
+@def_main
+def error(*argv):
+    print('error!')
+    return 1
+
+
+@def_main
+def never_reached(*argv):
+    print('This is never reached')
+    return 0