diff --git a/interp.py b/interp.py
index 31ff90b..38f447e 100644
--- a/interp.py
+++ b/interp.py
@@ -69,3 +69,10 @@
     else:
         print("Unknown command %s" % (ast))
         return None
+
+def run_ast(ast):
+    env = {
+        "System": system_module,
+    }
+    for command in ast:
+        run_command(env, command)
diff --git a/main.py b/main.py
index 98c776d..3a06c06 100755
--- a/main.py
+++ b/main.py
@@ -14,11 +14,7 @@
     ast = parse.parse_file(args[1])
     if not ast:
         return 1
-    env = {
-        "System": interp.system_module,
-    }
-    for command in ast:
-        interp.run_command(env, command)
+    interp.run_ast(ast)
     return 0
 
 if __name__ == "__main__":