Update serialization of cf variables

Author: cthoyt

src/y0/dsl.py

@@ -345,7 +345,12 @@ def to_latex(self) -> str:
 
     def to_y0(self) -> str:
         """Output this counterfactual variable instance as y0 internal DSL code."""
-        prefix = "~" if self.star else ""
+        if self.star is None:
+            prefix = ""
+        elif self.star:
+            prefix = "+"
+        else:
+            prefix = "-"
         if len(self.interventions) == 1:
             return f"{prefix}{self.name} @ {self.interventions[0].to_y0()}"
         else:

tests/test_dsl.py

@@ -119,13 +119,34 @@ def test_counterfactual_variable(self):
     def test_star_counterfactual(self):
         """Tests for generalized counterfactual variables."""
         for expr, expected in [
+            # Single variable
             (P(Y @ X), "P(Y @ X)"),
-            (P(~Y @ X), "P(~Y @ X)"),
+            (P(Y @ -X), "P(Y @ X)"),
             (P(Y @ ~X), "P(Y @ ~X)"),
-            (P(~Y @ ~X), "P(~Y @ ~X)"),
+            (P(Y @ +X), "P(Y @ ~X)"),
+            #
+            (P(-Y @ X), "P(-Y @ X)"),
+            (P(-Y @ -X), "P(-Y @ X)"),
+            (P(-Y @ ~X), "P(-Y @ ~X)"),
+            (P(-Y @ +X), "P(-Y @ ~X)"),
+            #
+            (P(~Y @ X), "P(+Y @ X)"),
+            (P(~Y @ -X), "P(+Y @ X)"),
+            (P(~Y @ ~X), "P(+Y @ ~X)"),
+            (P(~Y @ +X), "P(+Y @ ~X)"),
+            #
+            (P(+Y @ X), "P(+Y @ X)"),
+            (P(+Y @ -X), "P(+Y @ X)"),
+            (P(+Y @ ~X), "P(+Y @ ~X)"),
+            (P(+Y @ +X), "P(+Y @ ~X)"),
+            #
             (P(Y @ X | ~X, ~Y), "P(Y @ X | ~X, ~Y)"),
-            (P(~(Y @ ~X) | X, Y), "P(~Y @ ~X | X, Y)"),
-            (P(~Y @ ~X | X, Y), "P(~Y @ ~X | X, Y)"),  # should be same as above
+            (P(Y @ -X | ~X, ~Y), "P(Y @ X | ~X, ~Y)"),
+            (P(Y @ +X | ~X, ~Y), "P(Y @ ~X | ~X, ~Y)"),
+            (P(Y @ ~X | ~X, ~Y), "P(Y @ ~X | ~X, ~Y)"),
+            #
+            (P(~(Y @ ~X) | X, Y), "P(+Y @ ~X | X, Y)"),
+            (P(~Y @ ~X | X, Y), "P(+Y @ ~X | X, Y)"),  # should be same as above
         ]:
             with self.subTest(expr=expected):
                 self.assert_exp(expr, expected)