Use NotImplementedError for backend limitations.

src/pydiverse/transform/core/expressions/translator.py

@@ -35,7 +35,10 @@ def translate(self, expr, **kwargs) -> T:
         try:
             return bottom_up_replace(expr, lambda e: self._translate(e, **kwargs))
         except Exception as e:
-            raise ValueError(
+            etype = ValueError
+            if isinstance(e, NotImplementedError):
+                etype = NotImplementedError
+            raise etype(
                 "An exception occured while trying to translate the expression"
                 f" '{expr}':\n{e}"
             ) from e

src/pydiverse/transform/eager/pandas_table.py

@@ -444,7 +444,7 @@ def _translate(self, expr, **kwargs):
                     return ((c1, c2),)
                 if expr.name == "__and__":
                     return tuple(itertools.chain(*expr.args))
-            raise Exception(
+            raise NotImplementedError(
                 f"Invalid ON clause element: {expr}. Only a conjunction of equalities"
                 " is supported by pandas (ands of equals)."
             )

tests/test_backend_equivalence.py

@@ -23,6 +23,7 @@
     collect,
     filter,
     group_by,
+    inner_join,
     join,
     left_join,
     mutate,
@@ -559,6 +560,25 @@ def self_join_3(t):
 
         assert_result_equal(df3_x, df3_y, self_join_3)
 
+    @tables(["df1", "df2"], expect_not_implemented=["pandas"])
+    def test_inequality_join(self, df1_x, df1_y, df2_x, df2_y):
+        assert_result_equal(
+            (df1_x, df2_x),
+            (df1_y, df2_y),
+            lambda t, u: t
+            >> select()
+            >> inner_join(u, (t.col1 >= u.col1) & (t.col1 <= u.col1))
+            >> full_sort(),
+        )
+
+        assert_result_equal(
+            (df1_x, df2_x),
+            (df1_y, df2_y),
+            lambda t, u: t
+            >> inner_join(u >> select(), ~((t.col1 < u.col1) | (t.col1 > u.col1)))
+            >> full_sort(),
+        )
+
 
 class TestFilter:
     @tables(["df2"])