Add subclass checks to ProperSequence

Author: brandonwillard

cons/core.py

@@ -172,7 +172,7 @@ def __init__(self):
         raise NotImplementedError()
 
 
-class ProperSequenceType(ABCMeta):
+class ProperSequenceType(MaybeConsType):
     """An abstract type that can be used as an instance check for proper sequences.
 
     A proper sequence is a sequence according to `cons` but not a `ConsPair`.

tests/test_cons.py

@@ -87,6 +87,12 @@ def test_proper_sequence_type():
     assert isinstance([], ProperSequence)
     assert isinstance((1, 2, 3), ProperSequence)
 
+    assert not issubclass(ConsPair, ProperSequence)
+    assert not issubclass(str, ProperSequence)
+    assert not issubclass(int, ProperSequence)
+    assert issubclass(list, ProperSequence)
+    assert issubclass(tuple, ProperSequence)
+
 
 def test_cons_join():