Gotta update() expression too.

If type vars get into the espression you have to keep them in sync with
the unification or you can lose information.


Some combinators can put symbols on the expression, you have to convert
those to type checkers or, as a hack, just look them up and run them.
This lets definitions work(-ish), ...

test/test_type_inference.py

@@ -90,11 +90,27 @@ class TestCombinators(TestMixin, unittest.TestCase):
   def test_nullary(self):
     expression = n1, n2, (mul, s2), (stack, s3), dip, infra, first
     f = [
-      (s1, (f1, (n1, (n2, s2)))),  # (-- n2 n1 f1)
-      (s1, (i1, (n1, (n2, s2)))),  # (-- n2 n1 i1)
+      (s1, (f1, (f2, (f3, s1)))),  # (-- f3 f2 f1)
+      (s1, (f1, (f2, (i1, s1)))),  # (-- i1 f2 f1)
+      (s1, (f1, (i1, (f2, s1)))),  # (-- f2 i1 f1)
+      (s1, (i1, (i2, (i3, s1)))),  # (-- i3 i2 i1)
       ]
     self.assertEqualTypeStructure(infr(expression), f)
 
+    expression = n1, n2, (mul, s2), nullary
+    self.assertEqualTypeStructure(infr(expression), f)
+
+  def test_nullary_too(self):
+    expression = (stack, s3), dip, infra, first
+    f = ((s1, (a1, s2)), (a1, (a1, s2)))  # (a1 [...1] -- a1 a1)
+    self.assertEqualTypeStructure(infr(expression), [f])
+
+    expression = nullary,
+    f = ((s1, (a1, s2)), (a1, (a1, s2)))  # (a1 [...1] -- a1 a1)
+    # Something's not quite right here...
+    e = infr(expression)
+    self.assertEqualTypeStructure(infr(expression), [f])
+
   def test_x(self):
     expression = (a1, (swap, ((dup, s2), (dip, s0)))), x
     f = (s0, ((a0, (swap, ((dup, s1), (dip, s2)))), (a1, (a1, s0))))
@@ -168,4 +184,4 @@ class TestYin(TestMixin, unittest.TestCase):
 
 
 if __name__ == '__main__':
-    unittest.main()
+    unittest.main() #defaultTest='TestCombinators.test_nullary_too')