use union

main.py

@@ -1,6 +1,7 @@
 import ast
 import os
 import sys
+from typing import Union
 
 
 def generate_error(kind, node):
@@ -245,8 +246,8 @@ def generate_function_def_body(indent, node):
 def generate_if_then_else(
     indent,
     condition: ast.expr,
-    success: ast.expr | list[ast.stmt],
-    error: ast.expr | list[ast.stmt],
+    success: Union[ast.expr, list[ast.stmt]],
+    error: Union[ast.expr, list[ast.stmt]],
 ):
     return generate_indent(indent) + "(* if *)\n" + \
         generate_indent(indent) + "M.if_then_else (|\n" + \