Fixed subtyping bug, if supertype is an Intersection

bcls/subtypes.py

@@ -56,9 +56,9 @@ def _check_subtype_rec(self, subtypes: deque[Type], supertype: Type) -> bool:
                     and self._check_subtype_rec(casted_r, r2)
                 )
             case Intersection(l, r):
-                return self._check_subtype_rec(subtypes, l) and self._check_subtype_rec(
-                    subtypes, r
-                )
+                return self._check_subtype_rec(
+                    subtypes.copy(), l
+                ) and self._check_subtype_rec(subtypes, r)
             case _:
                 raise TypeError(f"Unsupported type in check_subtype: {supertype}")
 

tests/test_subtype.py

@@ -0,0 +1,28 @@
+import logging
+import unittest
+from bcls import Constructor
+from bcls.subtypes import Subtypes
+from bcls.types import Intersection
+
+
+class TestSubtype(unittest.TestCase):
+    logger = logging.getLogger(__name__)
+    logging.basicConfig(
+        format="%(module)s %(levelname)s: %(message)s",
+        # level=logging.INFO,
+    )
+
+    def test_constructor_refl(self) -> None:
+        a = Constructor("A")
+        subtypes = Subtypes({})
+        self.assertTrue(subtypes.check_subtype(a, a))
+
+    def test_idempotence_right(self) -> None:
+        a = Constructor("A")
+
+        subtypes = Subtypes({})
+        self.assertTrue(subtypes.check_subtype(a, Intersection(a, a)))
+
+
+if __name__ == "__main__":
+    unittest.main()