From a8f2751fd471f96a662413580870debda747929a Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Fri, 5 Jun 2026 11:06:21 +0100
Subject: [PATCH 01/30] rename ParameterNode to DataNode

---
 examples/two_normal.ipynb                     | 12 +++++------
 src/causalprog/graph/__init__.py              |  2 +-
 src/causalprog/graph/graph.py                 | 10 ++++-----
 src/causalprog/graph/node/__init__.py         |  2 +-
 .../graph/node/{parameter.py => data.py}      | 21 +++++++------------
 tests/fixtures/graph.py                       | 20 ++++++++----------
 tests/test_algorithms/test_do.py              | 10 ++++-----
 .../test_associate_models_to_components.py    |  4 ++--
 tests/test_graph/test_model.py                | 10 ++++-----
 tests/test_graph/test_ordering.py             | 14 ++++++-------
 tests/test_graph/test_parameters.py           |  8 +++----
 11 files changed, 52 insertions(+), 61 deletions(-)
 rename src/causalprog/graph/node/{parameter.py => data.py} (62%)

diff --git a/examples/two_normal.ipynb b/examples/two_normal.ipynb
index 73fe43d..0123037 100644
--- a/examples/two_normal.ipynb
+++ b/examples/two_normal.ipynb
@@ -102,9 +102,9 @@
     "\n",
     "For each parameter and random variable (RV) in our causal problem, we need a node to represent it.\n",
     "\n",
-    "1. **Model Parameters** are represented with `ParameterNode`s. The model parameters are the set of variables that fully parametrise the (RVs that appear in the) DAG / causal problem.\n",
+    "1. **Model Parameters** are represented with `DataNode`s. The model parameters are the set of variables that fully parametrise the (RVs that appear in the) DAG / causal problem.\n",
     "   - In our example, these are the values $\\mu_X$ and $\\nu_Y$.\n",
-    "   - For each of these, we add a `ParameterNode`. \n",
+    "   - For each of these, we add a `DataNode`. \n",
     "   - Model parameters that are referenced in the `parameters` dictionary of a `DistributionNode` will be used when constructing the `DistributionNode`'s RV.\n",
     "\n",
     "2. **Derived (RV) Parameters** are parameters of RVs that are the result of sampling from a previous distribution, or take the value of a model parameter.\n",
@@ -126,9 +126,9 @@
    "source": [
     "from numpyro.distributions import Normal\n",
     "\n",
-    "from causalprog.graph import DistributionNode, ParameterNode\n",
+    "from causalprog.graph import DistributionNode, DataNode\n",
     "\n",
-    "graph.add_node(ParameterNode(label=\"mu_X\"))\n",
+    "graph.add_node(DataNode(label=\"mu_X\"))\n",
     "graph.add_node(\n",
     "    DistributionNode(\n",
     "        distribution=Normal,\n",
@@ -138,7 +138,7 @@
     "    )\n",
     ")\n",
     "\n",
-    "graph.add_node(ParameterNode(label=\"nu_Y\"))\n",
+    "graph.add_node(DataNode(label=\"nu_Y\"))\n",
     "graph.add_node(\n",
     "    DistributionNode(\n",
     "        distribution=Normal,\n",
@@ -162,7 +162,7 @@
     "\n",
     "Note that edges should be directed **into** the dependent RV.\n",
     "That is, `DistributionNode`s should have edges directed into them from the nodes referenced by their derived parameters.\n",
-    "These nodes may be either `ParameterNode`s; for example our RV $X$ will need an edge from the `ParameterNode` for $\\mu_X$ into the `DistributionNode` representing $X$.\n",
+    "These nodes may be either `DataNode`s; for example our RV $X$ will need an edge from the `DataNode` for $\\mu_X$ into the `DistributionNode` representing $X$.\n",
     "They may also be other `DistributionNode`s; for example, $Y$ has $X$ as a derived parameter since we know that $Y \\vert X \\sim \\mathcal{N}(X, \\nu_Y)$."
    ]
   },
diff --git a/src/causalprog/graph/__init__.py b/src/causalprog/graph/__init__.py
index f1358ab..1fa4396 100644
--- a/src/causalprog/graph/__init__.py
+++ b/src/causalprog/graph/__init__.py
@@ -1,4 +1,4 @@
 """Creation and storage of graphs."""
 
 from .graph import Graph
-from .node import ComponentNode, DistributionNode, Node, ParameterNode
+from .node import ComponentNode, DistributionNode, Node, DataNode
diff --git a/src/causalprog/graph/graph.py b/src/causalprog/graph/graph.py
index de565fd..e252bd0 100644
--- a/src/causalprog/graph/graph.py
+++ b/src/causalprog/graph/graph.py
@@ -209,7 +209,7 @@ def model(self, **parameter_values: npt.ArrayLike) -> dict[str, npt.ArrayLike]:
 
         The model created takes values of the nodes that are parameter as keyword
         arguments. Names of the keyword arguments should match the labels of the
-        `ParameterNode`s, and their values should be the values of those parameters.
+        `DataNode`s, and their values should be the values of those parameters.
 
         The method returns a dictionary recording the mode sites that are created.
         This means that the model can be 'extended' further by defining additional
@@ -217,18 +217,18 @@ def model(self, **parameter_values: npt.ArrayLike) -> dict[str, npt.ArrayLike]:
 
         Args:
             parameter_values: Names of the keyword arguments should match the labels
-                of the `ParameterNode`s, and their values should be the values of those
+                of the `DataNode`s, and their values should be the values of those
                 parameters.
 
         Returns:
-            Mapping of non-`ParameterNode` `Node` labels to the site objects created
+            Mapping of non-`DataNode` `Node` labels to the site objects created
                 for these nodes.
 
         """
-        # Confirm that all `ParameterNode`s have been assigned a value.
+        # Confirm that all `DataNode`s have been assigned a value.
         for node in self.parameter_nodes:
             if node.label not in parameter_values:
-                msg = f"ParameterNode '{node.label}' not assigned"
+                msg = f"DataNode '{node.label}' not assigned"
                 raise KeyError(msg)
 
         # Build model sequentially, using the node_order to inform the
diff --git a/src/causalprog/graph/node/__init__.py b/src/causalprog/graph/node/__init__.py
index 13e66b5..f2a1866 100644
--- a/src/causalprog/graph/node/__init__.py
+++ b/src/causalprog/graph/node/__init__.py
@@ -3,4 +3,4 @@
 from .base import Node
 from .component import ComponentNode
 from .distribution import DistributionNode
-from .parameter import ParameterNode
+from .data import DataNode
diff --git a/src/causalprog/graph/node/parameter.py b/src/causalprog/graph/node/data.py
similarity index 62%
rename from src/causalprog/graph/node/parameter.py
rename to src/causalprog/graph/node/data.py
index 1bcceb7..6b701d3 100644
--- a/src/causalprog/graph/node/parameter.py
+++ b/src/causalprog/graph/node/data.py
@@ -1,4 +1,4 @@
-"""Graph nodes representing parameters."""
+"""Graph nodes representing known of unknown data."""
 
 import jax
 import jax.numpy as jnp
@@ -8,18 +8,11 @@
 from .base import Node
 
 
-class ParameterNode(Node):
+class DataNode(Node):
     """
-    A node containing a parameter.
+    A node containing non-stochastic data.
 
-    `ParameterNode`s differ from `DistributionNode`s in that they do not have an
-    attached distribution, but rather represent a parameter that contributes
-    to the shape of one (or more) `DistributionNode`s.
-
-    The collection of parameters described by `ParameterNode`s forms the set of
-    variables that will be optimised over in the corresponding `CausalProblem`.
-
-    `ParameterNode`s should not be used to encode constant values used by
+    `DataNode`s should not be used to encode constant values used by
     `DistributionNode`s. Such constant values should be given to the necessary
     `DistributionNode`s directly as `constant_parameters`.
     """
@@ -44,17 +37,17 @@ def sample(
         rng_key: jax.Array,
     ) -> npt.ArrayLike:
         if self.label not in parameter_values:
-            msg = f"Missing input for parameter node: {self.label}."
+            msg = f"Missing input for node: {self.label}."
             raise ValueError(msg)
         return jnp.full(samples, parameter_values[self.label])
 
     @override
     def copy(self) -> Node:
-        return ParameterNode(label=self.label)
+        return DataNode(label=self.label)
 
     @override
     def __repr__(self) -> str:
-        return f'ParameterNode(label="{self.label}")'
+        return f'DataNode(label="{self.label}")'
 
     @override
     @property
diff --git a/tests/fixtures/graph.py b/tests/fixtures/graph.py
index 62143d6..f7e93ae 100644
--- a/tests/fixtures/graph.py
+++ b/tests/fixtures/graph.py
@@ -8,19 +8,17 @@
 import pytest
 from numpyro.distributions import Normal
 
-from causalprog.graph import DistributionNode, Graph, ParameterNode
+from causalprog.graph import DistributionNode, Graph, DataNode
 
 NormalGraphNodeNames: TypeAlias = Literal["mean", "cov", "outcome"]
-NormalGraphNodes: TypeAlias = dict[
-    NormalGraphNodeNames, DistributionNode | ParameterNode
-]
+NormalGraphNodes: TypeAlias = dict[NormalGraphNodeNames, DistributionNode | DataNode]
 
 
 @pytest.fixture
 def normal_graph() -> Callable[[float, float], Graph]:
     """Creates a graph with one normal distribution X.
 
-    Parameter nodes are included if no values are given for the mean and covariance.
+    Data nodes are included if no values are given for the mean and covariance.
     """
 
     def _inner(mean: float | None = None, cov: float | None = None):
@@ -28,12 +26,12 @@ def _inner(mean: float | None = None, cov: float | None = None):
         parameters = {}
         constant_parameters = {}
         if mean is None:
-            graph.add_node(ParameterNode(label="mean"))
+            graph.add_node(DataNode(label="mean"))
             parameters["loc"] = "mean"
         else:
             constant_parameters["loc"] = mean
         if cov is None:
-            graph.add_node(ParameterNode(label="cov"))
+            graph.add_node(DataNode(label="cov"))
             parameters["scale"] = "cov"
         else:
             constant_parameters["scale"] = cov
@@ -61,7 +59,7 @@ def two_normal_graph() -> Callable[[float, float, float], Graph]:
     where UX is a normal distribution with mean `mean` and covariance `cov`, and X is
     a normal distrubution with mean UX and covariance `cov2`.
 
-    Parameter nodes are included if no values are given for the mean and covariances.
+    Data nodes are included if no values are given for the mean and covariances.
 
     """
 
@@ -75,17 +73,17 @@ def _inner(
         ux_parameters = {}
         ux_constant_parameters = {}
         if mean is None:
-            graph.add_node(ParameterNode(label="mean"))
+            graph.add_node(DataNode(label="mean"))
             ux_parameters["loc"] = "mean"
         else:
             ux_constant_parameters["loc"] = mean
         if cov is None:
-            graph.add_node(ParameterNode(label="cov"))
+            graph.add_node(DataNode(label="cov"))
             ux_parameters["scale"] = "cov"
         else:
             ux_constant_parameters["scale"] = cov
         if cov2 is None:
-            graph.add_node(ParameterNode(label="cov2"))
+            graph.add_node(DataNode(label="cov2"))
             x_parameters["scale"] = "cov2"
         else:
             x_constant_parameters["scale"] = cov2
diff --git a/tests/test_algorithms/test_do.py b/tests/test_algorithms/test_do.py
index a13f496..1599ffe 100644
--- a/tests/test_algorithms/test_do.py
+++ b/tests/test_algorithms/test_do.py
@@ -1,7 +1,7 @@
 """Tests for the do algorithm."""
 
 from causalprog import algorithms
-from causalprog.graph import Graph, ParameterNode
+from causalprog.graph import Graph, DataNode
 
 max_samples = 10**5
 
@@ -56,10 +56,10 @@ def test_do_edges(two_normal_graph):
 
 def test_do_error(raises_context):
     graph = Graph(label="ABC")
-    graph.add_node(ParameterNode(label="A"))
-    graph.add_node(ParameterNode(label="B1"))
-    graph.add_node(ParameterNode(label="B2"))
-    graph.add_node(ParameterNode(label="C"))
+    graph.add_node(DataNode(label="A"))
+    graph.add_node(DataNode(label="B1"))
+    graph.add_node(DataNode(label="B2"))
+    graph.add_node(DataNode(label="C"))
     graph.add_edge("A", "B1")
     graph.add_edge("A", "B2")
     graph.add_edge("B1", "C")
diff --git a/tests/test_causal_problem/test_associate_models_to_components.py b/tests/test_causal_problem/test_associate_models_to_components.py
index 631f44b..caac467 100644
--- a/tests/test_causal_problem/test_associate_models_to_components.py
+++ b/tests/test_causal_problem/test_associate_models_to_components.py
@@ -21,7 +21,7 @@
     Constraint,
     HandlerToApply,
 )
-from causalprog.graph import Graph, ParameterNode
+from causalprog.graph import Graph, DataNode
 
 
 @pytest.fixture
@@ -30,7 +30,7 @@ def underlying_graph() -> Graph:
     so we just return a single node graph.
     """
     g = Graph(label="Placeholder")
-    g.add_node(ParameterNode(label="p"))
+    g.add_node(DataNode(label="p"))
     return g
 
 
diff --git a/tests/test_graph/test_model.py b/tests/test_graph/test_model.py
index 26e0b04..db44ec0 100644
--- a/tests/test_graph/test_model.py
+++ b/tests/test_graph/test_model.py
@@ -2,7 +2,7 @@
 import numpyro
 import pytest
 
-from causalprog.graph import DistributionNode, Graph, ParameterNode
+from causalprog.graph import DistributionNode, Graph, DataNode
 
 
 @pytest.mark.parametrize(
@@ -21,7 +21,7 @@ def test_model(
 ) -> None:
     """Test the `Graph.model` method.
 
-    `Graph.model` takes values for the `ParameterNode`s (parameters of the model)
+    `Graph.model` takes values for the `DataNode`s (parameters of the model)
     as its arguments. It is designed to be able to be used just like any other
     function defining a model, namely that `Graph.model(**parameter_values)`
     is a function that creates the appropriate model sites, given values for the
@@ -52,14 +52,14 @@ def test_model_missing_parameter(
     seed: int,
 ) -> None:
     """`Graph.model` will raise a `KeyError` when a value is not passed for
-    a `ParameterNode`.
+    a `DataNode`.
     """
     graph = two_normal_graph(cov=1.0)
 
     # Deliberately leave out the "cov2" variable.
     parameter_values = {"mean": 0.0}
     # Which should result in the error below.
-    expected_exception = KeyError("ParameterNode 'cov2' not assigned")
+    expected_exception = KeyError("DataNode 'cov2' not assigned")
 
     # Not passing enough parameters should be picked up by the model.
     with raises_context(expected_exception), numpyro.handlers.seed(rng_seed=seed):
@@ -77,7 +77,7 @@ def test_model_extension(
     parameter_values = {"mean": 0.0, "cov2": 1.0}
 
     # Build the graph, but without the X-node.
-    mean = ParameterNode(label="mean")
+    mean = DataNode(label="mean")
     x = DistributionNode(
         numpyro.distributions.Normal,
         label="UX",
diff --git a/tests/test_graph/test_ordering.py b/tests/test_graph/test_ordering.py
index 57ba0a1..2ef804d 100644
--- a/tests/test_graph/test_ordering.py
+++ b/tests/test_graph/test_ordering.py
@@ -1,17 +1,17 @@
 """Tests for ordering of nodes in a graph."""
 
-from causalprog.graph import Graph, ParameterNode
+from causalprog.graph import Graph, DataNode
 
 
 def test_roots_down_to_outcome() -> None:
     graph = Graph(label="G0")
 
-    graph.add_node(ParameterNode(label="U"))
-    graph.add_node(ParameterNode(label="V"))
-    graph.add_node(ParameterNode(label="W"))
-    graph.add_node(ParameterNode(label="X"))
-    graph.add_node(ParameterNode(label="Y"))
-    graph.add_node(ParameterNode(label="Z"))
+    graph.add_node(DataNode(label="U"))
+    graph.add_node(DataNode(label="V"))
+    graph.add_node(DataNode(label="W"))
+    graph.add_node(DataNode(label="X"))
+    graph.add_node(DataNode(label="Y"))
+    graph.add_node(DataNode(label="Z"))
 
     edges = [
         ["V", "W"],
diff --git a/tests/test_graph/test_parameters.py b/tests/test_graph/test_parameters.py
index 589ddbe..8712ee9 100644
--- a/tests/test_graph/test_parameters.py
+++ b/tests/test_graph/test_parameters.py
@@ -2,13 +2,13 @@
 
 import jax.numpy as jnp
 
-from causalprog.graph import ParameterNode
+from causalprog.graph import DataNode
 
 
-def test_parameter_node(rng_key, raises_context):
-    node = ParameterNode(label="mu")
+def test_data_node(rng_key, raises_context):
+    node = DataNode(label="mu")
 
-    with raises_context(ValueError("Missing input for parameter")):
+    with raises_context(ValueError("Missing input for node")):
         node.sample({}, {}, 1, rng_key=rng_key)
 
     assert jnp.allclose(

From df6bf524073e348093ced4d825041693863955d0 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Fri, 5 Jun 2026 11:31:47 +0100
Subject: [PATCH 02/30] add evaluate method

---
 src/causalprog/graph/node/base.py         | 16 ++++++++++++++++
 src/causalprog/graph/node/component.py    |  7 +++++++
 src/causalprog/graph/node/data.py         | 18 ++++++++++++++++++
 src/causalprog/graph/node/distribution.py |  8 ++++++++
 tests/test_algorithms/test_evaluate.py    | 14 ++++++++++++++
 5 files changed, 63 insertions(+)
 create mode 100644 tests/test_algorithms/test_evaluate.py

diff --git a/src/causalprog/graph/node/base.py b/src/causalprog/graph/node/base.py
index f0d74b8..ce5318d 100644
--- a/src/causalprog/graph/node/base.py
+++ b/src/causalprog/graph/node/base.py
@@ -127,6 +127,22 @@ def sample(
 
         """
 
+    @abstractmethod
+    def evaluate(
+        self,
+        **given_values: dict[str, float | npt.NDArray[float]],
+    ) -> float | npt.NDArray[float]:
+        """
+        Evaluate the node.
+
+        Args:
+            given_values: Values for data nodes and values of parents
+
+        Returns:
+            Value of this node given the given values
+
+        """
+
     @abstractmethod
     def copy(self) -> Node:
         """
diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index f5d7ca1..ea8aa07 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -48,6 +48,13 @@ def sample(
     ) -> npt.NDArray[float]:
         return sampled_dependencies[self._parent_node_label][:, *self._component]
 
+    @override
+    def evaluate(
+        self,
+        **given_values: dict[str, float | npt.NDArray[float]],
+    ) -> float | npt.NDArray[float]:
+        return given_values[self._parent_node_label][*self.component]
+
     @override
     def copy(self) -> Node:
         return ComponentNode(
diff --git a/src/causalprog/graph/node/data.py b/src/causalprog/graph/node/data.py
index 6b701d3..ac92887 100644
--- a/src/causalprog/graph/node/data.py
+++ b/src/causalprog/graph/node/data.py
@@ -41,6 +41,24 @@ def sample(
             raise ValueError(msg)
         return jnp.full(samples, parameter_values[self.label])
 
+    @override
+    def evaluate(
+        self,
+        **given_values: dict[str, float | npt.NDArray[float]],
+    ) -> float | npt.NDArray[float]:
+        if self.label not in given_values:
+            msg = f"Missing input for node: {self.label}."
+            raise ValueError(msg)
+        value = given_values[self.label]
+        if self.shape == ():
+            if not isinstance(value, float):
+                msg = f"Invalid value for note: {self.label}"
+                raise ValueError(msg)
+        elif isinstance(value, float) or self.shape != value.shape:
+            msg = f"Invalid value for nose: {self.label}"
+            raise ValueError(msg)
+        return value
+
     @override
     def copy(self) -> Node:
         return DataNode(label=self.label)
diff --git a/src/causalprog/graph/node/distribution.py b/src/causalprog/graph/node/distribution.py
index 555672f..18f5abf 100644
--- a/src/causalprog/graph/node/distribution.py
+++ b/src/causalprog/graph/node/distribution.py
@@ -70,6 +70,14 @@ def sample(
             else self.shape,
         )
 
+    @override
+    def evaluate(
+        self,
+        **given_values: dict[str, float | npt.NDArray[float]],
+    ) -> float | npt.NDArray[float]:
+        msg = "Cannot evaluate a DistributionNode"
+        raise RuntimeError(msg)
+
     @override
     def copy(self) -> Node:
         return DistributionNode(
diff --git a/tests/test_algorithms/test_evaluate.py b/tests/test_algorithms/test_evaluate.py
new file mode 100644
index 0000000..105eb3b
--- /dev/null
+++ b/tests/test_algorithms/test_evaluate.py
@@ -0,0 +1,14 @@
+"""Tests for evaluate algorithms."""
+
+import numpy as np
+import jax.numpy as jnp
+import pytest
+from causalprog.graph import DataNode
+
+
+def test_evaluate_node(raises_context):
+    node = DataNode(label="A")
+    assert np.isclose(node.evaluate(A=2.0), 2.0)
+
+    with raises_context(ValueError("Missing input for node: A")):
+        node.evaluate()

From 1d0738df1b518507183ea23c7dc513846ad38f49 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Fri, 5 Jun 2026 11:45:12 +0100
Subject: [PATCH 03/30] mypy?

---
 src/causalprog/graph/node/component.py | 5 ++++-
 src/causalprog/graph/node/data.py      | 3 ++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index ea8aa07..71120ef 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import numpy as np
 import typing
 
 from typing_extensions import override
@@ -53,7 +54,9 @@ def evaluate(
         self,
         **given_values: dict[str, float | npt.NDArray[float]],
     ) -> float | npt.NDArray[float]:
-        return given_values[self._parent_node_label][*self.component]
+        parent_value = given_values[self._parent_node_label]
+        assert isinstance(parent_value, np.ndarray)
+        return parent_value[*self.component]
 
     @override
     def copy(self) -> Node:
diff --git a/src/causalprog/graph/node/data.py b/src/causalprog/graph/node/data.py
index ac92887..dbe0d43 100644
--- a/src/causalprog/graph/node/data.py
+++ b/src/causalprog/graph/node/data.py
@@ -2,6 +2,7 @@
 
 import jax
 import jax.numpy as jnp
+import numpy as np
 import numpy.typing as npt
 from typing_extensions import override
 
@@ -54,7 +55,7 @@ def evaluate(
             if not isinstance(value, float):
                 msg = f"Invalid value for note: {self.label}"
                 raise ValueError(msg)
-        elif isinstance(value, float) or self.shape != value.shape:
+        elif not isinstance(value, np.ndarray) or self.shape != value.shape:
             msg = f"Invalid value for nose: {self.label}"
             raise ValueError(msg)
         return value

From cbb10ea64ddc081e5bb825bd46f7fd0e2a247d40 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Fri, 5 Jun 2026 14:45:21 +0100
Subject: [PATCH 04/30] ruff

---
 src/causalprog/graph/node/component.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index 71120ef..e433bdc 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -55,7 +55,9 @@ def evaluate(
         **given_values: dict[str, float | npt.NDArray[float]],
     ) -> float | npt.NDArray[float]:
         parent_value = given_values[self._parent_node_label]
-        assert isinstance(parent_value, np.ndarray)
+        if not isinstance(parent_value, np.ndarray):
+            msg = f"Invalid data in node: {self._parent_node_label}"
+            raise ValueError(msg)
         return parent_value[*self.component]
 
     @override

From a956b83bcabeaf1715eb192fe58ef56983f3706f Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Fri, 5 Jun 2026 14:47:39 +0100
Subject: [PATCH 05/30] typeerror

---
 src/causalprog/graph/node/component.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index e433bdc..c32dc56 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -57,7 +57,7 @@ def evaluate(
         parent_value = given_values[self._parent_node_label]
         if not isinstance(parent_value, np.ndarray):
             msg = f"Invalid data in node: {self._parent_node_label}"
-            raise ValueError(msg)
+            raise TypeError(msg)
         return parent_value[*self.component]
 
     @override

From b7b3332c6011a284a09ffbd659778b59c7582596 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Fri, 5 Jun 2026 14:49:20 +0100
Subject: [PATCH 06/30] rufff

---
 examples/two_normal.ipynb                                      | 2 +-
 src/causalprog/graph/__init__.py                               | 2 +-
 src/causalprog/graph/node/__init__.py                          | 2 +-
 src/causalprog/graph/node/component.py                         | 2 +-
 tests/fixtures/graph.py                                        | 2 +-
 tests/test_algorithms/test_do.py                               | 2 +-
 tests/test_algorithms/test_evaluate.py                         | 3 +--
 .../test_causal_problem/test_associate_models_to_components.py | 2 +-
 tests/test_graph/test_model.py                                 | 2 +-
 tests/test_graph/test_ordering.py                              | 2 +-
 10 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/examples/two_normal.ipynb b/examples/two_normal.ipynb
index 0123037..8697c8d 100644
--- a/examples/two_normal.ipynb
+++ b/examples/two_normal.ipynb
@@ -126,7 +126,7 @@
    "source": [
     "from numpyro.distributions import Normal\n",
     "\n",
-    "from causalprog.graph import DistributionNode, DataNode\n",
+    "from causalprog.graph import DataNode, DistributionNode\n",
     "\n",
     "graph.add_node(DataNode(label=\"mu_X\"))\n",
     "graph.add_node(\n",
diff --git a/src/causalprog/graph/__init__.py b/src/causalprog/graph/__init__.py
index 1fa4396..20832aa 100644
--- a/src/causalprog/graph/__init__.py
+++ b/src/causalprog/graph/__init__.py
@@ -1,4 +1,4 @@
 """Creation and storage of graphs."""
 
 from .graph import Graph
-from .node import ComponentNode, DistributionNode, Node, DataNode
+from .node import ComponentNode, DataNode, DistributionNode, Node
diff --git a/src/causalprog/graph/node/__init__.py b/src/causalprog/graph/node/__init__.py
index f2a1866..a58bfc4 100644
--- a/src/causalprog/graph/node/__init__.py
+++ b/src/causalprog/graph/node/__init__.py
@@ -2,5 +2,5 @@
 
 from .base import Node
 from .component import ComponentNode
-from .distribution import DistributionNode
 from .data import DataNode
+from .distribution import DistributionNode
diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index c32dc56..39aaccd 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -2,9 +2,9 @@
 
 from __future__ import annotations
 
-import numpy as np
 import typing
 
+import numpy as np
 from typing_extensions import override
 
 from .base import Node
diff --git a/tests/fixtures/graph.py b/tests/fixtures/graph.py
index f7e93ae..d707f5b 100644
--- a/tests/fixtures/graph.py
+++ b/tests/fixtures/graph.py
@@ -8,7 +8,7 @@
 import pytest
 from numpyro.distributions import Normal
 
-from causalprog.graph import DistributionNode, Graph, DataNode
+from causalprog.graph import DataNode, DistributionNode, Graph
 
 NormalGraphNodeNames: TypeAlias = Literal["mean", "cov", "outcome"]
 NormalGraphNodes: TypeAlias = dict[NormalGraphNodeNames, DistributionNode | DataNode]
diff --git a/tests/test_algorithms/test_do.py b/tests/test_algorithms/test_do.py
index 1599ffe..6c89338 100644
--- a/tests/test_algorithms/test_do.py
+++ b/tests/test_algorithms/test_do.py
@@ -1,7 +1,7 @@
 """Tests for the do algorithm."""
 
 from causalprog import algorithms
-from causalprog.graph import Graph, DataNode
+from causalprog.graph import DataNode, Graph
 
 max_samples = 10**5
 
diff --git a/tests/test_algorithms/test_evaluate.py b/tests/test_algorithms/test_evaluate.py
index 105eb3b..a25fe24 100644
--- a/tests/test_algorithms/test_evaluate.py
+++ b/tests/test_algorithms/test_evaluate.py
@@ -1,8 +1,7 @@
 """Tests for evaluate algorithms."""
 
 import numpy as np
-import jax.numpy as jnp
-import pytest
+
 from causalprog.graph import DataNode
 
 
diff --git a/tests/test_causal_problem/test_associate_models_to_components.py b/tests/test_causal_problem/test_associate_models_to_components.py
index caac467..d444671 100644
--- a/tests/test_causal_problem/test_associate_models_to_components.py
+++ b/tests/test_causal_problem/test_associate_models_to_components.py
@@ -21,7 +21,7 @@
     Constraint,
     HandlerToApply,
 )
-from causalprog.graph import Graph, DataNode
+from causalprog.graph import DataNode, Graph
 
 
 @pytest.fixture
diff --git a/tests/test_graph/test_model.py b/tests/test_graph/test_model.py
index db44ec0..7a18b0d 100644
--- a/tests/test_graph/test_model.py
+++ b/tests/test_graph/test_model.py
@@ -2,7 +2,7 @@
 import numpyro
 import pytest
 
-from causalprog.graph import DistributionNode, Graph, DataNode
+from causalprog.graph import DataNode, DistributionNode, Graph
 
 
 @pytest.mark.parametrize(
diff --git a/tests/test_graph/test_ordering.py b/tests/test_graph/test_ordering.py
index 2ef804d..04407b1 100644
--- a/tests/test_graph/test_ordering.py
+++ b/tests/test_graph/test_ordering.py
@@ -1,6 +1,6 @@
 """Tests for ordering of nodes in a graph."""
 
-from causalprog.graph import Graph, DataNode
+from causalprog.graph import DataNode, Graph
 
 
 def test_roots_down_to_outcome() -> None:

From abbff6bdcf0076ea5fd79a65aceab2717f89b803 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Wed, 24 Jun 2026 14:58:20 +0100
Subject: [PATCH 07/30] simplify some graph code

---
 src/causalprog/algorithms/do.py           | 17 ++----
 src/causalprog/graph/__init__.py          |  2 +-
 src/causalprog/graph/graph.py             | 47 +++++++----------
 src/causalprog/graph/node/__init__.py     |  1 +
 src/causalprog/graph/node/base.py         | 51 ++----------------
 src/causalprog/graph/node/component.py    | 16 ++----
 src/causalprog/graph/node/constant.py     | 63 +++++++++++++++++++++++
 src/causalprog/graph/node/data.py         | 11 ++--
 src/causalprog/graph/node/distribution.py | 19 +++----
 tests/test_algorithms/test_do.py          | 19 ++++---
 10 files changed, 113 insertions(+), 133 deletions(-)
 create mode 100644 src/causalprog/graph/node/constant.py

diff --git a/src/causalprog/algorithms/do.py b/src/causalprog/algorithms/do.py
index 6e0688c..709ea31 100644
--- a/src/causalprog/algorithms/do.py
+++ b/src/causalprog/algorithms/do.py
@@ -2,7 +2,7 @@
 
 from copy import deepcopy
 
-from causalprog.graph import Graph, Node
+from causalprog.graph import Graph, Node, ConstantNode
 
 
 def get_included_excluded_successors(
@@ -72,19 +72,6 @@ def do(graph: Graph, node: str, value: float, label: str | None = None) -> Graph
 
     nodes = {n.label: deepcopy(n) for n in graph.nodes if n.label != node}
 
-    # Search through the old graph, identifying nodes that had parameters which were
-    # defined by the node being fixed in the DO operation.
-    # We recreate these nodes, but replace each such parameter we encounter with
-    # a constant parameter equal that takes the fixed value given as an input.
-    for n in nodes.values():
-        params = tuple(n.parameters.keys())
-        for parameter_name in params:
-            if n.parameters[parameter_name] == node:
-                # Swap the parameter to a constant parameter, giving it the fixed value
-                n.constant_parameters[parameter_name] = value
-                # Remove the parameter from the node's record of non-constant parameters
-                n.parameters.pop(parameter_name)
-
     # Recursively remove nodes that are predecessors of removed nodes
     nodes_to_remove: tuple[str, ...] = (node,)
     while len(nodes_to_remove) > 0:
@@ -103,6 +90,8 @@ def do(graph: Graph, node: str, value: float, label: str | None = None) -> Graph
             )
             raise ValueError(msg)
 
+    nodes[node] = ConstantNode(label=node, value=value)
+
     g = Graph(label=f"{label}|do[{node}={value}]")
     for n in nodes.values():
         g.add_node(n)
diff --git a/src/causalprog/graph/__init__.py b/src/causalprog/graph/__init__.py
index 20832aa..d4166bb 100644
--- a/src/causalprog/graph/__init__.py
+++ b/src/causalprog/graph/__init__.py
@@ -1,4 +1,4 @@
 """Creation and storage of graphs."""
 
 from .graph import Graph
-from .node import ComponentNode, DataNode, DistributionNode, Node
+from .node import ComponentNode, DataNode, DistributionNode, Node, ConstantNode
diff --git a/src/causalprog/graph/graph.py b/src/causalprog/graph/graph.py
index e252bd0..41ecaa7 100644
--- a/src/causalprog/graph/graph.py
+++ b/src/causalprog/graph/graph.py
@@ -4,7 +4,7 @@
 import numpy.typing as npt
 
 from causalprog._abc.labelled import Labelled
-from causalprog.graph.node import ComponentNode, Node
+from causalprog.graph.node import ComponentNode, Node, DistributionNode
 
 
 class Graph(Labelled):
@@ -61,7 +61,10 @@ def add_node(self, node: Node) -> None:
         self._nodes_by_label[node.label] = node
         self._graph.add_node(node)
         if isinstance(node, ComponentNode):
-            self.add_edge(node.parent_node, node.label)
+            if len(node.parents) != 1:
+                msg = "ComponentNode should have exactly one parent."
+                raise ValueError(msg)
+            self.add_edge(node.parents[0], node.label)
 
     def add_edge(self, start_node: Node | str, end_node: Node | str) -> None:
         """
@@ -91,22 +94,22 @@ def add_edge(self, start_node: Node | str, end_node: Node | str) -> None:
         self._graph.add_edge(start_node, end_node)
 
     @property
-    def parameter_nodes(self) -> tuple[Node, ...]:
+    def leaf_nodes(self) -> tuple[Node, ...]:
         """
-        Returns all parameter nodes in the graph.
+        Returns all leaf nodes in the graph.
 
-        The returned tuple uses the `ordered_nodes` property to obtain the parameter
-        nodes so that a natural "fixed order" is given to the parameters. When parameter
+        The returned tuple uses the `ordered_nodes` property to obtain the leaf
+        nodes so that a natural "fixed order" is given to the leaves. When leaf
         values are given as inputs to the causal estimand and / or constraint functions,
-        they will ideally be given as a single vector of parameter values, in which case
-        a fixed ordering for the parameters is necessary to make an association to the
+        they will ideally be given as a single vector of leaf values, in which case
+        a fixed ordering for the leaves is necessary to make an association to the
         components of the given input vector.
 
         Returns:
-            Parameter nodes
+            Leaf nodes
 
         """
-        return tuple(node for node in self.ordered_nodes if node.is_parameter)
+        return tuple(node for node in self.ordered_nodes if len(node.parents) == 0)
 
     @property
     def predecessors(self) -> dict[Node, tuple[Node, ...]]:
@@ -170,17 +173,6 @@ def ordered_nodes(self) -> tuple[Node, ...]:
             raise RuntimeError(msg)
         return tuple(nx.topological_sort(self._graph))
 
-    @property
-    def ordered_dist_nodes(self) -> tuple[Node, ...]:
-        """
-        `DistributionNode`s in dependency order.
-
-        Each `DistributionNode` in the returned list appears after all its
-        dependencies. Order is derived from `self.ordered_nodes`, selecting
-        only those nodes where `is_distribution` is `True`.
-        """
-        return tuple(node for node in self.ordered_nodes if node.is_distribution)
-
     def roots_down_to_outcome(
         self,
         outcome_node_label: str,
@@ -226,7 +218,7 @@ def model(self, **parameter_values: npt.ArrayLike) -> dict[str, npt.ArrayLike]:
 
         """
         # Confirm that all `DataNode`s have been assigned a value.
-        for node in self.parameter_nodes:
+        for node in self.leaf_nodes:
             if node.label not in parameter_values:
                 msg = f"DataNode '{node.label}' not assigned"
                 raise KeyError(msg)
@@ -234,10 +226,11 @@ def model(self, **parameter_values: npt.ArrayLike) -> dict[str, npt.ArrayLike]:
         # Build model sequentially, using the node_order to inform the
         # construction process.
         node_record: dict[str, npt.ArrayLike] = {}
-        for node in self.ordered_dist_nodes:
-            node_record[node.label] = node.create_model_site(
-                **parameter_values,  # All nodes require knowledge of the parameters
-                **node_record,  # and any dependent nodes we have already visited
-            )
+        for node in self.ordered_nodes:
+            if isinstance(node, DistributionNode):
+                node_record[node.label] = node.create_model_site(
+                    **parameter_values,  # All nodes require knowledge of the parameters
+                    **node_record,  # and any dependent nodes we have already visited
+                )
 
         return node_record
diff --git a/src/causalprog/graph/node/__init__.py b/src/causalprog/graph/node/__init__.py
index a58bfc4..1698224 100644
--- a/src/causalprog/graph/node/__init__.py
+++ b/src/causalprog/graph/node/__init__.py
@@ -2,5 +2,6 @@
 
 from .base import Node
 from .component import ComponentNode
+from .constant import ConstantNode
 from .data import DataNode
 from .distribution import DistributionNode
diff --git a/src/causalprog/graph/node/base.py b/src/causalprog/graph/node/base.py
index ce5318d..e3e6d1a 100644
--- a/src/causalprog/graph/node/base.py
+++ b/src/causalprog/graph/node/base.py
@@ -40,8 +40,6 @@ def __init__(
         *,
         label: str,
         shape: tuple[int, ...] = (),
-        is_parameter: bool = False,
-        is_distribution: bool = False,
     ) -> None:
         """
         Initialise.
@@ -55,23 +53,15 @@ def __init__(
         constraints), and as such the value that a "parameter node" passes to its
         dependent nodes will vary as the optimiser runs and explores the solution space.
 
-        Note that a "constant parameter" is distinct from a "parameter" in the sense
-        that a constant parameter is _not_ added to the collection of parameters over
-        which we will want to optimise (it is a hard-coded, fixed value).
-
         Distributions (equivalently `DistributionNode`s) are Nodes that represent
         random variables described by probability distributions.
 
         Args:
             label: A unique label to identify the node
             shape: The shape of the node's value for each sample
-            is_parameter: Is the node a parameter?
-            is_distribution: Is the node a distribution?
 
         """
         super().__init__(label=label)
-        self._is_parameter = is_parameter
-        self._is_distribution = is_distribution
         self._shape = shape
 
     def __getitem__(self, indices: int | slice | tuple[int | slice, ...]) -> Node:
@@ -168,48 +158,13 @@ def shape(self) -> tuple[int, ...]:
         """
         return self._shape
 
-    @property
-    def is_parameter(self) -> bool:
-        """
-        Identify if the node is an parameter.
-
-        Returns:
-            True if the node is an parameter
-
-        """
-        return self._is_parameter
-
-    @property
-    def is_distribution(self) -> bool:
-        """
-        Identify if the node is an distribution.
-
-        Returns:
-            True if the node is an distribution
-
-        """
-        return self._is_distribution
-
-    @property
-    @abstractmethod
-    def constant_parameters(self) -> dict[str, float]:
-        """
-        Named constants that this node depends on.
-
-        Returns:
-            A dictionary of the constant parameter names (keys) and their corresponding
-            values
-
-        """
-
     @property
     @abstractmethod
-    def parameters(self) -> dict[str, str]:
+    def parents(self) -> list[str]:
         """
-        Mapping of distribution parameter names to the nodes they are represented by.
+        Nodes that this node depends on the value of.
 
         Returns:
-            Mapping of distribution parameters (keys) to the corresponding label of the
-            node that represents this parameter (value).
+            List of labels of parent nodes
 
         """
diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index 39aaccd..8ec1c7a 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -36,7 +36,7 @@ def __init__(
         """
         self._component = component
         self._parent_node_label = parent_node_label
-        super().__init__(shape=shape, label=label, is_distribution=True)
+        super().__init__(shape=shape, label=label)
 
     @override
     def sample(
@@ -82,15 +82,5 @@ def __repr__(self) -> str:
 
     @override
     @property
-    def constant_parameters(self) -> dict[str, float]:
-        return {}
-
-    @override
-    @property
-    def parameters(self) -> dict[str, str]:
-        return {}
-
-    @property
-    def parent_node(self) -> str:
-        """The label of the parent node."""
-        return self._parent_node_label
+    def parents(self) -> list[str]:
+        return [self._parent_node_label]
diff --git a/src/causalprog/graph/node/constant.py b/src/causalprog/graph/node/constant.py
new file mode 100644
index 0000000..df8dc79
--- /dev/null
+++ b/src/causalprog/graph/node/constant.py
@@ -0,0 +1,63 @@
+"""Graph nodes representing distributions."""
+
+from __future__ import annotations
+
+import typing
+
+import numpy as np
+from typing_extensions import override
+
+from .base import Node
+
+if typing.TYPE_CHECKING:
+    import jax
+    import numpy.typing as npt
+
+
+class ConstantNode(Node):
+    """A node representing a constant."""
+
+    def __init__(self, *, label: str, value: flat | npt.NDArray[float]) -> None:
+        """
+        Initialise.
+
+        Args:
+            label: A unique label to identify the node
+            value: The value of this constant
+
+        """
+        self._value = value
+        super().__init__(
+            shape=() if isinstance(value, float) else value.shape, label=label
+        )
+
+    @override
+    def sample(
+        self,
+        parameter_values: dict[str, float],
+        sampled_dependencies: dict[str, npt.NDArray[float]],
+        samples: int,
+        *,
+        rng_key: jax.Array,
+    ) -> npt.NDArray[float]:
+        return jnp.full(samples, self._value)
+
+    @override
+    def evaluate(
+        self,
+        **given_values: dict[str, float | npt.NDArray[float]],
+    ) -> float | npt.NDArray[float]:
+        return self._value
+
+    @override
+    def copy(self) -> Node:
+        return ConstantNode(label=self.label, value=self._value)
+
+    @override
+    def __repr__(self) -> str:
+        r = f"ConstantNode({self._value})"
+
+    @override
+    @property
+    def parents(self) -> list[str]:
+        return []
diff --git a/src/causalprog/graph/node/data.py b/src/causalprog/graph/node/data.py
index dbe0d43..c9eb729 100644
--- a/src/causalprog/graph/node/data.py
+++ b/src/causalprog/graph/node/data.py
@@ -26,7 +26,7 @@ def __init__(self, *, shape: tuple[int, ...] = (), label: str) -> None:
             label: A unique label to identify the node
 
         """
-        super().__init__(label=label, shape=shape, is_parameter=True)
+        super().__init__(label=label, shape=shape)
 
     @override
     def sample(
@@ -70,10 +70,5 @@ def __repr__(self) -> str:
 
     @override
     @property
-    def constant_parameters(self) -> dict[str, float]:
-        return {}
-
-    @override
-    @property
-    def parameters(self) -> dict[str, str]:
-        return {}
+    def parents(self) -> list[str]:
+        return []
diff --git a/src/causalprog/graph/node/distribution.py b/src/causalprog/graph/node/distribution.py
index 18f5abf..30495f9 100644
--- a/src/causalprog/graph/node/distribution.py
+++ b/src/causalprog/graph/node/distribution.py
@@ -40,7 +40,7 @@ def __init__(
         self._dist = distribution
         self._constant_parameters = constant_parameters if constant_parameters else {}
         self._parameters = parameters if parameters else {}
-        super().__init__(label=label, shape=shape, is_distribution=True)
+        super().__init__(label=label, shape=shape)
 
     @override
     def sample(
@@ -55,10 +55,10 @@ def sample(
             # Pass in node values derived from construction so far
             **{
                 native_name: sampled_dependencies[node_name]
-                for native_name, node_name in self.parameters.items()
+                for native_name, node_name in self._parameters.items()
             },
             # Pass in any constant parameters this node sets
-            **self.constant_parameters,
+            **self._constant_parameters,
         )
 
         return numpyro.sample(
@@ -101,13 +101,8 @@ def __repr__(self) -> str:
 
     @override
     @property
-    def constant_parameters(self) -> dict[str, float]:
-        return self._constant_parameters
-
-    @override
-    @property
-    def parameters(self) -> dict[str, str]:
-        return self._parameters
+    def parents(self) -> list[str]:
+        return list(self._parameters.keys()) + list(self._constant_parameters.keys())
 
     def create_model_site(self, **dependent_nodes: jax.Array) -> npt.ArrayLike:
         """
@@ -125,9 +120,9 @@ def create_model_site(self, **dependent_nodes: jax.Array) -> npt.ArrayLike:
                 # Pass in node values derived from construction so far
                 **{
                     native_name: dependent_nodes[node_name]
-                    for native_name, node_name in self.parameters.items()
+                    for native_name, node_name in self._parameters.items()
                 },
                 # Pass in any constant parameters this node sets
-                **self.constant_parameters,
+                **self._constant_parameters,
             ),
         )
diff --git a/tests/test_algorithms/test_do.py b/tests/test_algorithms/test_do.py
index 6c89338..4977c70 100644
--- a/tests/test_algorithms/test_do.py
+++ b/tests/test_algorithms/test_do.py
@@ -1,30 +1,29 @@
 """Tests for the do algorithm."""
 
 from causalprog import algorithms
-from causalprog.graph import DataNode, Graph
+from causalprog.graph import DataNode, Graph, ConstantNode
 
 max_samples = 10**5
 
 
-def test_do(two_normal_graph, raises_context):
+def test_do(two_normal_graph):
     graph = two_normal_graph(5.0, 1.2, 0.8)
     graph2 = algorithms.do(graph, "UX", 4.0)
 
-    assert "loc" in graph.get_node("X").parameters
-    assert "loc" not in graph.get_node("X").constant_parameters
-    assert "loc" not in graph2.get_node("X").parameters
-    assert "loc" in graph2.get_node("X").constant_parameters
+    assert "loc" in graph.get_node("X").parents
+    assert "loc" in graph2.get_node("X").parents
 
     graph.get_node("UX")
-    with raises_context(KeyError('Node not found with label "UX"')):
-        graph2.get_node("UX")
+    assert isinstance(graph2.get_node("UX"), ConstantNode)
 
 
 def test_do_removes_dependencies(two_normal_graph, raises_context):
     graph = two_normal_graph()
     graph2 = algorithms.do(graph, "UX", 4.0)
 
-    for node in ["UX", "mean", "cov"]:
+    graph.get_node("UX")
+    assert isinstance(graph2.get_node("UX"), ConstantNode)
+    for node in ["mean", "cov"]:
         graph.get_node(node)
         with raises_context(KeyError(f'Node not found with label "{node}"')):
             graph2.get_node(node)
@@ -39,7 +38,6 @@ def test_do_edges(two_normal_graph):
 
     # Check that correct edges are removed
     for e in [
-        ("UX", "X"),
         ("mean", "UX"),
         ("cov", "UX"),
     ]:
@@ -48,6 +46,7 @@ def test_do_edges(two_normal_graph):
 
     # Check that correct edges remain
     for e in [
+        ("UX", "X"),
         ("cov2", "X"),
     ]:
         assert e in edges

From 43149c55455eec62fe0e342858fce686c7a78640 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 08:59:03 +0100
Subject: [PATCH 08/30] Update src/causalprog/graph/node/base.py

Co-authored-by: Will Graham <32364977+willGraham01@users.noreply.github.com>
---
 src/causalprog/graph/node/base.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/causalprog/graph/node/base.py b/src/causalprog/graph/node/base.py
index ce5318d..0f81ffe 100644
--- a/src/causalprog/graph/node/base.py
+++ b/src/causalprog/graph/node/base.py
@@ -139,7 +139,7 @@ def evaluate(
             given_values: Values for data nodes and values of parents
 
         Returns:
-            Value of this node given the given values
+            Value of this node given `given_values`.
 
         """
 

From 6e6826423baeefa469f4a02fc829765ba66a2e92 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 08:59:21 +0100
Subject: [PATCH 09/30] Update src/causalprog/graph/node/base.py

Co-authored-by: Will Graham <32364977+willGraham01@users.noreply.github.com>
---
 src/causalprog/graph/node/base.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/causalprog/graph/node/base.py b/src/causalprog/graph/node/base.py
index 0f81ffe..204fe6a 100644
--- a/src/causalprog/graph/node/base.py
+++ b/src/causalprog/graph/node/base.py
@@ -133,7 +133,7 @@ def evaluate(
         **given_values: dict[str, float | npt.NDArray[float]],
     ) -> float | npt.NDArray[float]:
         """
-        Evaluate the node.
+        Evaluate the node, given evaluations of its precursor nodes.
 
         Args:
             given_values: Values for data nodes and values of parents

From 8f64aa42487234569aed2304213dc5cf49798cd5 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:00:20 +0100
Subject: [PATCH 10/30] Update tests/test_algorithms/test_evaluate.py

Co-authored-by: Will Graham <32364977+willGraham01@users.noreply.github.com>
---
 tests/test_algorithms/test_evaluate.py | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/tests/test_algorithms/test_evaluate.py b/tests/test_algorithms/test_evaluate.py
index a25fe24..2047578 100644
--- a/tests/test_algorithms/test_evaluate.py
+++ b/tests/test_algorithms/test_evaluate.py
@@ -5,9 +5,24 @@
 from causalprog.graph import DataNode
 
 
-def test_evaluate_node(raises_context):
-    node = DataNode(label="A")
-    assert np.isclose(node.evaluate(A=2.0), 2.0)
+@pytest.mark.parametrize(
+    ("node", "kwargs_to_evaluate", "expected_result"),
+    [
+        pytest.param(DataNode(label="A"), {"A": 2.0}, 2.0, id="Evaluate DataNode itself"),
+        # Likely want a test here for a ComponentNode?
+        pytest.param(ComponentNode("Parent", 1, label="Child"), {"Parent": np.arange(4)}, 1.0, id="Evaluate ComponentNode, given parent"),
+    ]
+)
+def test_evaluate_node(node, kwargs_to_evaluate, expected_result):
+    assert np.allclose(node.evaluate(**kwargs_to_evaluate), expected_result)
 
-    with raises_context(ValueError("Missing input for node: A")):
-        node.evaluate()
+@pytest.mark.parametrize(
+    ("node", "kwargs_for_evaluate", "expected_error"),
+    [
+        pytest.param(DataNode(label="A"), {}, ValueError("Missing input for node: A"), id="DataNode missing input value"),
+        pytest.param(DistributionNode(dist=None, label="A"), {}, ValueError("Cannot evaluate a DistributionNode"), id="Attempt to evaluate DistributionNode"),
+    ]
+)
+def test_evaluate_node_fail_on_missing_data(node, kwargs_for_evaluate, expected_error, raises_context):
+    with raises_context(expected_error):
+        node.evaluate(**kwargs_for_evaluate)

From 752005ace0d1133d6500b55aebea81feab8caf62 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:00:50 +0100
Subject: [PATCH 11/30] Apply suggestion from @mscroggs

---
 tests/test_algorithms/test_evaluate.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/tests/test_algorithms/test_evaluate.py b/tests/test_algorithms/test_evaluate.py
index 2047578..b6f5b64 100644
--- a/tests/test_algorithms/test_evaluate.py
+++ b/tests/test_algorithms/test_evaluate.py
@@ -9,7 +9,6 @@
     ("node", "kwargs_to_evaluate", "expected_result"),
     [
         pytest.param(DataNode(label="A"), {"A": 2.0}, 2.0, id="Evaluate DataNode itself"),
-        # Likely want a test here for a ComponentNode?
         pytest.param(ComponentNode("Parent", 1, label="Child"), {"Parent": np.arange(4)}, 1.0, id="Evaluate ComponentNode, given parent"),
     ]
 )

From 7f1db29691ffaa87bd5fd3f443b7264370fe19da Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:12:32 +0100
Subject: [PATCH 12/30] fix tests

---
 src/causalprog/graph/node/component.py     |  8 +++--
 tests/test_algorithms/test_evaluate.py     | 37 +++++++++++++++++-----
 tests/test_causal_problem/test_handlers.py |  2 +-
 3 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index 39aaccd..d9b8c67 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -20,7 +20,7 @@ class ComponentNode(Node):
     def __init__(
         self,
         parent_node_label: str,
-        component: tuple[int, ...],
+        component: int | tuple[int, ...],
         *,
         shape: tuple[int, ...] = (),
         label: str,
@@ -34,7 +34,9 @@ def __init__(
             label: A unique label to identify the node
 
         """
-        self._component = component
+        self._component = (
+            (component,) if isinstance(component, int) else tuple(component)
+        )
         self._parent_node_label = parent_node_label
         super().__init__(shape=shape, label=label, is_distribution=True)
 
@@ -58,7 +60,7 @@ def evaluate(
         if not isinstance(parent_value, np.ndarray):
             msg = f"Invalid data in node: {self._parent_node_label}"
             raise TypeError(msg)
-        return parent_value[*self.component]
+        return parent_value[*self._component]
 
     @override
     def copy(self) -> Node:
diff --git a/tests/test_algorithms/test_evaluate.py b/tests/test_algorithms/test_evaluate.py
index b6f5b64..0a1dcbc 100644
--- a/tests/test_algorithms/test_evaluate.py
+++ b/tests/test_algorithms/test_evaluate.py
@@ -1,27 +1,48 @@
 """Tests for evaluate algorithms."""
 
 import numpy as np
+import pytest
 
-from causalprog.graph import DataNode
+from causalprog.graph import DataNode, ComponentNode, DistributionNode
 
 
 @pytest.mark.parametrize(
     ("node", "kwargs_to_evaluate", "expected_result"),
     [
-        pytest.param(DataNode(label="A"), {"A": 2.0}, 2.0, id="Evaluate DataNode itself"),
-        pytest.param(ComponentNode("Parent", 1, label="Child"), {"Parent": np.arange(4)}, 1.0, id="Evaluate ComponentNode, given parent"),
-    ]
+        pytest.param(
+            DataNode(label="A"), {"A": 2.0}, 2.0, id="Evaluate DataNode itself"
+        ),
+        pytest.param(
+            ComponentNode("Parent", 1, label="Child"),
+            {"Parent": np.arange(4)},
+            1.0,
+            id="Evaluate ComponentNode, given parent",
+        ),
+    ],
 )
 def test_evaluate_node(node, kwargs_to_evaluate, expected_result):
     assert np.allclose(node.evaluate(**kwargs_to_evaluate), expected_result)
 
+
 @pytest.mark.parametrize(
     ("node", "kwargs_for_evaluate", "expected_error"),
     [
-        pytest.param(DataNode(label="A"), {}, ValueError("Missing input for node: A"), id="DataNode missing input value"),
-        pytest.param(DistributionNode(dist=None, label="A"), {}, ValueError("Cannot evaluate a DistributionNode"), id="Attempt to evaluate DistributionNode"),
-    ]
+        pytest.param(
+            DataNode(label="A"),
+            {},
+            ValueError("Missing input for node: A"),
+            id="DataNode missing input value",
+        ),
+        pytest.param(
+            DistributionNode(distribution=None, label="A"),
+            {},
+            RuntimeError("Cannot evaluate a DistributionNode"),
+            id="Attempt to evaluate DistributionNode",
+        ),
+    ],
 )
-def test_evaluate_node_fail_on_missing_data(node, kwargs_for_evaluate, expected_error, raises_context):
+def test_evaluate_node_fail_on_missing_data(
+    node, kwargs_for_evaluate, expected_error, raises_context
+):
     with raises_context(expected_error):
         node.evaluate(**kwargs_for_evaluate)
diff --git a/tests/test_causal_problem/test_handlers.py b/tests/test_causal_problem/test_handlers.py
index 3801201..494e234 100644
--- a/tests/test_causal_problem/test_handlers.py
+++ b/tests/test_causal_problem/test_handlers.py
@@ -6,7 +6,7 @@
 
 def placeholder_callable() -> EffectHandler:
     """Stand-in for an effect handler."""
-    return lambda model, **kwargs: (lambda **pv: model(**kwargs))
+    return lambda model, **kwargs: lambda **pv: model(**kwargs)
 
 
 @pytest.mark.parametrize(

From 5ed79b5911ea68d7322b495c0ad11567210d88da Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:19:12 +0100
Subject: [PATCH 13/30] ruff

---
 src/causalprog/algorithms/moments.py      | 2 +-
 src/causalprog/graph/node/distribution.py | 4 ++--
 src/causalprog/utils/translator.py        | 4 +---
 tests/test_algorithms/test_evaluate.py    | 2 +-
 4 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/src/causalprog/algorithms/moments.py b/src/causalprog/algorithms/moments.py
index d6f9801..6ce14ef 100644
--- a/src/causalprog/algorithms/moments.py
+++ b/src/causalprog/algorithms/moments.py
@@ -22,7 +22,7 @@ def sample(
 
     for node, key in zip(nodes, keys, strict=False):
         values[node.label] = node.sample(
-            parameter_values if parameter_values else {},
+            parameter_values or {},
             values,
             samples,
             rng_key=key,
diff --git a/src/causalprog/graph/node/distribution.py b/src/causalprog/graph/node/distribution.py
index 18f5abf..9e9f2a3 100644
--- a/src/causalprog/graph/node/distribution.py
+++ b/src/causalprog/graph/node/distribution.py
@@ -38,8 +38,8 @@ def __init__(
 
         """
         self._dist = distribution
-        self._constant_parameters = constant_parameters if constant_parameters else {}
-        self._parameters = parameters if parameters else {}
+        self._constant_parameters = constant_parameters or {}
+        self._parameters = parameters or {}
         super().__init__(label=label, shape=shape, is_distribution=True)
 
     @override
diff --git a/src/causalprog/utils/translator.py b/src/causalprog/utils/translator.py
index 0e26eba..8e6e0bd 100644
--- a/src/causalprog/utils/translator.py
+++ b/src/causalprog/utils/translator.py
@@ -72,9 +72,7 @@ def __init__(
 
         """
         # Assume backend name is identical to frontend name if not provided explicitly
-        self.backend_method = (
-            backend_method if backend_method else self._frontend_method
-        )
+        self.backend_method = backend_method or self._frontend_method
 
         # This should really be immutable after we fill defaults!
         self.corresponding_backend_arg = dict(front_args_to_back_args)
diff --git a/tests/test_algorithms/test_evaluate.py b/tests/test_algorithms/test_evaluate.py
index 0a1dcbc..6475c8f 100644
--- a/tests/test_algorithms/test_evaluate.py
+++ b/tests/test_algorithms/test_evaluate.py
@@ -3,7 +3,7 @@
 import numpy as np
 import pytest
 
-from causalprog.graph import DataNode, ComponentNode, DistributionNode
+from causalprog.graph import ComponentNode, DataNode, DistributionNode
 
 
 @pytest.mark.parametrize(

From bb1b0f3aea1412348fbb77c163a157598ce7d0f9 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:32:48 +0100
Subject: [PATCH 14/30] hasattr(..., "shape") instead of type check

---
 src/causalprog/graph/node/data.py | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/src/causalprog/graph/node/data.py b/src/causalprog/graph/node/data.py
index dbe0d43..9b93df9 100644
--- a/src/causalprog/graph/node/data.py
+++ b/src/causalprog/graph/node/data.py
@@ -2,7 +2,6 @@
 
 import jax
 import jax.numpy as jnp
-import numpy as np
 import numpy.typing as npt
 from typing_extensions import override
 
@@ -51,12 +50,8 @@ def evaluate(
             msg = f"Missing input for node: {self.label}."
             raise ValueError(msg)
         value = given_values[self.label]
-        if self.shape == ():
-            if not isinstance(value, float):
-                msg = f"Invalid value for note: {self.label}"
-                raise ValueError(msg)
-        elif not isinstance(value, np.ndarray) or self.shape != value.shape:
-            msg = f"Invalid value for nose: {self.label}"
+        if self.shape != (value.shape if hasattr(value, "shape") else ()):
+            msg = f"Invalid value for node: {self.label}"
             raise ValueError(msg)
         return value
 

From 2c23e019bdc433fd61f8ffb956928ab7d92d046e Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:34:29 +0100
Subject: [PATCH 15/30] let KeyError happen rather than asserting types

---
 src/causalprog/graph/node/component.py | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index d9b8c67..42fba2c 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -56,11 +56,7 @@ def evaluate(
         self,
         **given_values: dict[str, float | npt.NDArray[float]],
     ) -> float | npt.NDArray[float]:
-        parent_value = given_values[self._parent_node_label]
-        if not isinstance(parent_value, np.ndarray):
-            msg = f"Invalid data in node: {self._parent_node_label}"
-            raise TypeError(msg)
-        return parent_value[*self._component]
+        return given_values[self._parent_node_label][*self._component]
 
     @override
     def copy(self) -> Node:

From 2815ff876a2c6b3cde1e49dae232dd8c641bdba9 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:40:13 +0100
Subject: [PATCH 16/30] mypy?

---
 src/causalprog/graph/node/component.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index 42fba2c..be7634e 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -56,7 +56,8 @@ def evaluate(
         self,
         **given_values: dict[str, float | npt.NDArray[float]],
     ) -> float | npt.NDArray[float]:
-        return given_values[self._parent_node_label][*self._component]
+        parent_value = given_values[self._parent_node_label]
+        return parent_value[*self._component]
 
     @override
     def copy(self) -> Node:

From 42a28449648133cc50d0858944373669e0a64835 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:42:28 +0100
Subject: [PATCH 17/30] currect type

---
 src/causalprog/graph/node/base.py         | 2 +-
 src/causalprog/graph/node/component.py    | 5 ++---
 src/causalprog/graph/node/data.py         | 2 +-
 src/causalprog/graph/node/distribution.py | 2 +-
 4 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/causalprog/graph/node/base.py b/src/causalprog/graph/node/base.py
index 204fe6a..ffbfb46 100644
--- a/src/causalprog/graph/node/base.py
+++ b/src/causalprog/graph/node/base.py
@@ -130,7 +130,7 @@ def sample(
     @abstractmethod
     def evaluate(
         self,
-        **given_values: dict[str, float | npt.NDArray[float]],
+        **given_values: float | npt.NDArray[float],
     ) -> float | npt.NDArray[float]:
         """
         Evaluate the node, given evaluations of its precursor nodes.
diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index be7634e..607b474 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -54,10 +54,9 @@ def sample(
     @override
     def evaluate(
         self,
-        **given_values: dict[str, float | npt.NDArray[float]],
+        **given_values: float | npt.NDArray[float],
     ) -> float | npt.NDArray[float]:
-        parent_value = given_values[self._parent_node_label]
-        return parent_value[*self._component]
+        return given_values[self._parent_node_label][*self._component]
 
     @override
     def copy(self) -> Node:
diff --git a/src/causalprog/graph/node/data.py b/src/causalprog/graph/node/data.py
index 9b93df9..29a5c69 100644
--- a/src/causalprog/graph/node/data.py
+++ b/src/causalprog/graph/node/data.py
@@ -44,7 +44,7 @@ def sample(
     @override
     def evaluate(
         self,
-        **given_values: dict[str, float | npt.NDArray[float]],
+        **given_values: float | npt.NDArray[float],
     ) -> float | npt.NDArray[float]:
         if self.label not in given_values:
             msg = f"Missing input for node: {self.label}."
diff --git a/src/causalprog/graph/node/distribution.py b/src/causalprog/graph/node/distribution.py
index 9e9f2a3..811a801 100644
--- a/src/causalprog/graph/node/distribution.py
+++ b/src/causalprog/graph/node/distribution.py
@@ -73,7 +73,7 @@ def sample(
     @override
     def evaluate(
         self,
-        **given_values: dict[str, float | npt.NDArray[float]],
+        **given_values: float | npt.NDArray[float],
     ) -> float | npt.NDArray[float]:
         msg = "Cannot evaluate a DistributionNode"
         raise RuntimeError(msg)

From 2e1eb1b64e5ee17e7572c67d3eeb103bf3633d64 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:44:01 +0100
Subject: [PATCH 18/30] type: ignore

---
 src/causalprog/graph/node/component.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index 607b474..b401d64 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -4,7 +4,6 @@
 
 import typing
 
-import numpy as np
 from typing_extensions import override
 
 from .base import Node
@@ -56,7 +55,8 @@ def evaluate(
         self,
         **given_values: float | npt.NDArray[float],
     ) -> float | npt.NDArray[float]:
-        return given_values[self._parent_node_label][*self._component]
+        parent_value = given_values[self._parent_node_label]
+        return parent_value[*self._component]  # type: ignore
 
     @override
     def copy(self) -> Node:

From dae7e6bdd77d08f1c4cef946c2aae8d025321338 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:46:56 +0100
Subject: [PATCH 19/30] PGH003

---
 src/causalprog/graph/node/component.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/causalprog/graph/node/component.py b/src/causalprog/graph/node/component.py
index b401d64..b774949 100644
--- a/src/causalprog/graph/node/component.py
+++ b/src/causalprog/graph/node/component.py
@@ -56,7 +56,7 @@ def evaluate(
         **given_values: float | npt.NDArray[float],
     ) -> float | npt.NDArray[float]:
         parent_value = given_values[self._parent_node_label]
-        return parent_value[*self._component]  # type: ignore
+        return parent_value[*self._component]  # type: ignore[index]
 
     @override
     def copy(self) -> Node:

From 5717c16b119a530d22ac6998cf0ba0989b968805 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:50:07 +0100
Subject: [PATCH 20/30] typing

---
 src/causalprog/graph/node/constant.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/causalprog/graph/node/constant.py b/src/causalprog/graph/node/constant.py
index 6856142..3b5bb52 100644
--- a/src/causalprog/graph/node/constant.py
+++ b/src/causalprog/graph/node/constant.py
@@ -44,7 +44,7 @@ def sample(
     @override
     def evaluate(
         self,
-        **given_values: dict[str, float | npt.NDArray[float]],
+        **given_values: float | npt.NDArray[float],
     ) -> float | npt.NDArray[float]:
         return self._value
 

From 209b86e238fb837c4bd35dad32bf29deba5f7119 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 09:55:08 +0100
Subject: [PATCH 21/30] corrections

---
 src/causalprog/graph/node/constant.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/causalprog/graph/node/constant.py b/src/causalprog/graph/node/constant.py
index 3b5bb52..f49a2d3 100644
--- a/src/causalprog/graph/node/constant.py
+++ b/src/causalprog/graph/node/constant.py
@@ -4,6 +4,7 @@
 
 import typing
 
+import jax.numpy as jnp
 from typing_extensions import override
 
 from .base import Node
@@ -16,7 +17,7 @@
 class ConstantNode(Node):
     """A node representing a constant."""
 
-    def __init__(self, *, label: str, value: flat | npt.NDArray[float]) -> None:
+    def __init__(self, *, label: str, value: float | npt.NDArray[float]) -> None:
         """
         Initialise.
 
@@ -54,7 +55,7 @@ def copy(self) -> Node:
 
     @override
     def __repr__(self) -> str:
-        r = f"ConstantNode({self._value})"
+        return f"ConstantNode({self._value})"
 
     @override
     @property

From 06d0f69cf7a55e94b8f8360ca473216198efaa7c Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 10:37:59 +0100
Subject: [PATCH 22/30] add check that labels are valid variable names

---
 src/causalprog/_abc/labelled.py  |  3 +++
 tests/test__abc/test_labelled.py | 29 +++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 tests/test__abc/test_labelled.py

diff --git a/src/causalprog/_abc/labelled.py b/src/causalprog/_abc/labelled.py
index 92250bc..b62770e 100644
--- a/src/causalprog/_abc/labelled.py
+++ b/src/causalprog/_abc/labelled.py
@@ -20,4 +20,7 @@ def label(self) -> str:
         return self._label
 
     def __init__(self, *, label: str) -> None:
+        if not str.isidentifier(label):
+            msg = f"Label is not valid Python variable name: {label}"
+            raise ValueError(msg)
         self._label = str(label)
diff --git a/tests/test__abc/test_labelled.py b/tests/test__abc/test_labelled.py
new file mode 100644
index 0000000..10c469d
--- /dev/null
+++ b/tests/test__abc/test_labelled.py
@@ -0,0 +1,29 @@
+import pytest
+from causalprog._abc.labelled import Labelled
+
+
+@pytest.mark.parametrize("label", [
+    "1",
+    " ",
+    "a b",
+    "0a",
+    "a.b",
+    "a-b",
+    "a+b",
+    "a*b",
+    "a/b",
+])
+def test_invalid_label(label, raises_context):
+    with raises_context(ValueError("Label is not valid Python variable name")):
+        Labelled(label=label)
+
+
+@pytest.mark.parametrize("label", [
+    "a",
+    "A",
+    "a0",
+    "a_b",
+    "_a",
+])
+def test_valid_label(label, raises_context):
+    Labelled(label=label)

From 7700ea5ba21a24edd2849dce3be412ae95fee16f Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 10:38:31 +0100
Subject: [PATCH 23/30] ruff

---
 tests/test__abc/test_labelled.py | 43 +++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 18 deletions(-)

diff --git a/tests/test__abc/test_labelled.py b/tests/test__abc/test_labelled.py
index 10c469d..6d53372 100644
--- a/tests/test__abc/test_labelled.py
+++ b/tests/test__abc/test_labelled.py
@@ -1,29 +1,36 @@
 import pytest
+
 from causalprog._abc.labelled import Labelled
 
 
-@pytest.mark.parametrize("label", [
-    "1",
-    " ",
-    "a b",
-    "0a",
-    "a.b",
-    "a-b",
-    "a+b",
-    "a*b",
-    "a/b",
-])
+@pytest.mark.parametrize(
+    "label",
+    [
+        "1",
+        " ",
+        "a b",
+        "0a",
+        "a.b",
+        "a-b",
+        "a+b",
+        "a*b",
+        "a/b",
+    ],
+)
 def test_invalid_label(label, raises_context):
     with raises_context(ValueError("Label is not valid Python variable name")):
         Labelled(label=label)
 
 
-@pytest.mark.parametrize("label", [
-    "a",
-    "A",
-    "a0",
-    "a_b",
-    "_a",
-])
+@pytest.mark.parametrize(
+    "label",
+    [
+        "a",
+        "A",
+        "a0",
+        "a_b",
+        "_a",
+    ],
+)
 def test_valid_label(label, raises_context):
     Labelled(label=label)

From 29f7679d8a2b12b0b850b334455d4449754881d0 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 10:50:28 +0100
Subject: [PATCH 24/30] update tests and labels

---
 src/causalprog/graph/node/base.py  | 8 ++++----
 tests/test_graph/test_component.py | 6 +++---
 tests/test_graph/test_model.py     | 2 +-
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/causalprog/graph/node/base.py b/src/causalprog/graph/node/base.py
index ee6a89a..e7d4f54 100644
--- a/src/causalprog/graph/node/base.py
+++ b/src/causalprog/graph/node/base.py
@@ -15,18 +15,18 @@
 def _to_string(indices: int | slice | tuple[int | slice, ...]) -> str:
     """Convert getitem indices to a string."""
     if isinstance(indices, tuple):
-        return ", ".join(_to_string(i) for i in indices)
+        return "_".join(_to_string(i) for i in indices)
     if isinstance(indices, int):
         return f"{indices}"
     if isinstance(indices, slice):
         s = ""
         if indices.start is not None:
             s += f"{indices.start}"
-        s += ":"
+        s += "__"
         if indices.stop is not None:
             s += f"{indices.stop}"
         if indices.step is not None:
-            s += f":{indices.step}"
+            s += f"__{indices.step}"
         return s
     e = f"Invalid indices: {indices}"
     raise TypeError(e)
@@ -91,7 +91,7 @@ def __getitem__(self, indices: int | slice | tuple[int | slice, ...]) -> Node:
             self.label,
             indices,
             shape=shape,
-            label=f"{self.label}[{_to_string(indices)}]",
+            label=f"{self.label}_{_to_string(indices)}",
         )
 
     @abstractmethod
diff --git a/tests/test_graph/test_component.py b/tests/test_graph/test_component.py
index 9a417b8..3c6b356 100644
--- a/tests/test_graph/test_component.py
+++ b/tests/test_graph/test_component.py
@@ -26,6 +26,6 @@ def test_component_node(param_values):
     graph.add_node(graph.get_node("X")[1, :, 2])
 
     assert graph.get_node("X").shape == (3, 1, 4)
-    assert graph.get_node("X[0]").shape == (1, 4)
-    assert graph.get_node("X[1, 0, 2]").shape == ()
-    assert graph.get_node("X[1, :, 2]").shape == (1,)
+    assert graph.get_node("X_0").shape == (1, 4)
+    assert graph.get_node("X_1_0_2").shape == ()
+    assert graph.get_node("X_1____2").shape == (1,)
diff --git a/tests/test_graph/test_model.py b/tests/test_graph/test_model.py
index 7a18b0d..1f3e38d 100644
--- a/tests/test_graph/test_model.py
+++ b/tests/test_graph/test_model.py
@@ -84,7 +84,7 @@ def test_model_extension(
         parameters={"loc": "mean"},
         constant_parameters={"scale": 1.0},
     )
-    one_normal_graph = Graph(label="One normal")
+    one_normal_graph = Graph(label="One_normal")
     one_normal_graph.add_edge(mean, x)
 
     def extended_model(*, cov2, **parameter_values):

From ac099fea157563a5dcf6f642190a7c51c1287073 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 14:07:38 +0100
Subject: [PATCH 25/30] Add random variable nodes

---
 src/causalprog/graph/__init__.py              |  10 +-
 src/causalprog/graph/node/__init__.py         |   1 +
 src/causalprog/graph/node/random_variables.py | 135 ++++++++++++++++++
 tests/test_graph/test_random_variables.py     |  35 +++++
 4 files changed, 180 insertions(+), 1 deletion(-)
 create mode 100644 src/causalprog/graph/node/random_variables.py
 create mode 100644 tests/test_graph/test_random_variables.py

diff --git a/src/causalprog/graph/__init__.py b/src/causalprog/graph/__init__.py
index 0825556..02eb604 100644
--- a/src/causalprog/graph/__init__.py
+++ b/src/causalprog/graph/__init__.py
@@ -1,4 +1,12 @@
 """Creation and storage of graphs."""
 
 from .graph import Graph
-from .node import ComponentNode, ConstantNode, DataNode, DistributionNode, Node
+from .node import (
+    ComponentNode,
+    ConstantNode,
+    ContinuousRandomVariableNode,
+    DataNode,
+    DiscreteRandomVariableNode,
+    DistributionNode,
+    Node,
+)
diff --git a/src/causalprog/graph/node/__init__.py b/src/causalprog/graph/node/__init__.py
index 1698224..a6acf66 100644
--- a/src/causalprog/graph/node/__init__.py
+++ b/src/causalprog/graph/node/__init__.py
@@ -5,3 +5,4 @@
 from .constant import ConstantNode
 from .data import DataNode
 from .distribution import DistributionNode
+from .random_variables import ContinuousRandomVariableNode, DiscreteRandomVariableNode
diff --git a/src/causalprog/graph/node/random_variables.py b/src/causalprog/graph/node/random_variables.py
new file mode 100644
index 0000000..9b9d580
--- /dev/null
+++ b/src/causalprog/graph/node/random_variables.py
@@ -0,0 +1,135 @@
+"""Graph nodes representing random variables."""
+
+import inspect
+import typing
+from abc import abstractmethod
+
+import jax
+import numpy as np
+import numpy.typing as npt
+from typing_extensions import override
+
+from .base import Node
+
+
+class RandomVariableNode(Node):
+    """A node containing a random variable (RV)."""
+
+    def __init__(
+        self,
+        *,
+        shape: tuple[int, ...] = (),
+        label: str,
+        compute: typing.Callable | None = None,
+    ) -> None:
+        """
+        Initialise.
+
+        Args:
+            shape: The shape of the output of the RV
+            label: A unique label to identify the node
+            compute: A function to compute this node's value from given values of its parent nodes
+
+        """
+        super().__init__(label=label, shape=shape)
+        if compute is None:
+            self._parents = []
+        else:
+            self._parents = list(inspect.signature(compute).parameters.keys())
+        self._compute = compute
+
+    @override
+    def sample(
+        self,
+        parameter_values: dict[str, float],
+        sampled_dependencies: dict[str, npt.ArrayLike],
+        samples: int,
+        *,
+        rng_key: jax.Array,
+    ) -> npt.ArrayLike:
+        raise NotImplementedError
+
+    @override
+    def evaluate(
+        self,
+        **given_values: float | npt.NDArray[float],
+    ) -> float | npt.NDArray[float]:
+        if self.label in given_values:
+            value = given_values[self.label]
+            if not self.is_valid_value(value):
+                msg = f"Invalid value for {self.__class__.__name__}: {self.label} cannot be {value}"
+                raise ValueError(msg)
+            if self.shape != (value.shape if hasattr(value, "shape") else ()):
+                msg = f"Invalid value for node: {self.label}"
+                raise ValueError(msg)
+            return value
+
+        if self._compute is None:
+            msg = f"Missing input for node: {self.label}."
+            raise ValueError(msg)
+        return self._compute(**{p: given_values[p] for p in self._parents})
+
+    @override
+    def copy(self) -> Node:
+        return DataNode(label=self.label)
+
+    @override
+    @property
+    def parents(self) -> list[str]:
+        return self._parents
+
+    @abstractmethod
+    def is_valid_value(self, value: float | npt.NDArray[float]):
+        """Check if a value is valid for this node."""
+
+
+class ContinuousRandomVariableNode(RandomVariableNode):
+    """A node containing a continuous random variable (RV)."""
+
+    @override
+    def __repr__(self) -> str:
+        return f'ContinuousRandomVariableNode(label="{self.label}")'
+
+    @override
+    def is_valid_value(self, value: float | npt.NDArray[float]) -> bool:
+        return True
+
+
+class DiscreteRandomVariableNode(RandomVariableNode):
+    """A node containing a discrete random variable (RV)."""
+
+    def __init__(
+        self,
+        *,
+        values: list[float] | list[npt.NDArray[float]],
+        shape: tuple[int, ...] = (),
+        label: str,
+        compute: typing.Callable | None = None,
+    ) -> None:
+        """
+        Initialise.
+
+        Args:
+            shape: The shape of the output of the RV
+            label: A unique label to identify the node
+            compute: A function to compute this node's value from given values of its parent nodes
+
+        """
+        super().__init__(label=label, shape=shape, compute=compute)
+        self._values = values
+
+    @property
+    def possible_values(self) -> list[float] | list[npt.NDArray[float]]:
+        """The values that this RV can take."""
+        return self._values
+
+    @override
+    def __repr__(self) -> str:
+        return f'DiscreteRandomVariableNode(label="{self.label}")'
+
+    @override
+    def is_valid_value(self, value: float | npt.NDArray[float]) -> bool:
+        for v in self._values:
+            if np.allclose(v, value):
+                return True
+        return False
diff --git a/tests/test_graph/test_random_variables.py b/tests/test_graph/test_random_variables.py
new file mode 100644
index 0000000..e2fabd3
--- /dev/null
+++ b/tests/test_graph/test_random_variables.py
@@ -0,0 +1,35 @@
+import numpy as np
+
+from causalprog.graph import (
+    ContinuousRandomVariableNode,
+    DiscreteRandomVariableNode,
+    Graph,
+)
+
+
+def test_random_variable_node():
+    node = ContinuousRandomVariableNode(label="X")
+    assert np.isclose(node.evaluate(X=2.0), 2.0)
+
+
+def test_missing_input(raises_context):
+    node = ContinuousRandomVariableNode(label="X")
+
+    with raises_context(ValueError("Missing input for node")):
+        node.evaluate()
+
+
+def test_invalid_discrete_node_value(raises_context):
+    node = DiscreteRandomVariableNode(label="Y", values=[-0.5, 0.0, 0.5])
+    with raises_context(ValueError("Invalid value for DiscreteRandomVariableNode")):
+        node.evaluate(Y=-1.0)
+
+
+def test_sum_parents():
+    graph = Graph(label="G")
+
+    graph.add_node(ContinuousRandomVariableNode(label="X"))
+    graph.add_node(DiscreteRandomVariableNode(label="Y", values=[-0.5, 0.0, 0.5]))
+    graph.add_node(ContinuousRandomVariableNode(label="Z", compute=lambda X, Y: X + Y))
+
+    assert np.isclose(graph.get_node("Z").evaluate(X=3.0, Y=-0.5), 2.5)

From 30c0216ce5c2a82ebd075fddf62b801b6b1aabeb Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 14:30:48 +0100
Subject: [PATCH 26/30] ruff

---
 src/causalprog/algorithms/do.py               |  4 +--
 src/causalprog/graph/node/random_variables.py | 28 ++++++++++++++-----
 .../test_random_variables.py                  |  8 +++---
 tests/test_node/test_vector_nodes.py          |  2 +-
 4 files changed, 28 insertions(+), 14 deletions(-)
 rename tests/{test_graph => test_node}/test_random_variables.py (73%)

diff --git a/src/causalprog/algorithms/do.py b/src/causalprog/algorithms/do.py
index 9b53b97..9c0d6f9 100644
--- a/src/causalprog/algorithms/do.py
+++ b/src/causalprog/algorithms/do.py
@@ -68,7 +68,7 @@ def do(graph: Graph, node: str, value: float, label: str | None = None) -> Graph
 
     """
     if label is None:
-        label = f"{graph.label}|do({node}={value})"
+        label = f"{graph.label}_do_{node}__" + f"{value}".replace(".", "_")
 
     nodes = {n.label: deepcopy(n) for n in graph.nodes if n.label != node}
 
@@ -92,7 +92,7 @@ def do(graph: Graph, node: str, value: float, label: str | None = None) -> Graph
 
     nodes[node] = ConstantNode(label=node, value=value)
 
-    g = Graph(label=f"{label}|do[{node}={value}]")
+    g = Graph(label=f"{label}_do_{node}__" + f"{value}".replace(".", "_"))
     for n in nodes.values():
         g.add_node(n)
 
diff --git a/src/causalprog/graph/node/random_variables.py b/src/causalprog/graph/node/random_variables.py
index 9b9d580..79fd619 100644
--- a/src/causalprog/graph/node/random_variables.py
+++ b/src/causalprog/graph/node/random_variables.py
@@ -28,7 +28,7 @@ def __init__(
         Args:
             shape: The shape of the output of the RV
             label: A unique label to identify the node
-            compute: A function to compute this node's value from given values of its parent nodes
+            compute: A function to compute node's value from given values of parents
 
         """
         super().__init__(label=label, shape=shape)
@@ -57,7 +57,10 @@ def evaluate(
         if self.label in given_values:
             value = given_values[self.label]
             if not self.is_valid_value(value):
-                msg = f"Invalid value for {self.__class__.__name__}: {self.label} cannot be {value}"
+                msg = (
+                    f"Invalid value for {self.__class__.__name__}: "
+                    f"{self.label} cannot be {value}"
+                )
                 raise ValueError(msg)
             if self.shape != (value.shape if hasattr(value, "shape") else ()):
                 msg = f"Invalid value for node: {self.label}"
@@ -69,10 +72,6 @@ def evaluate(
             raise ValueError(msg)
         return self._compute(**{p: given_values[p] for p in self._parents})
 
-    @override
-    def copy(self) -> Node:
-        return DataNode(label=self.label)
-
     @override
     @property
     def parents(self) -> list[str]:
@@ -94,6 +93,12 @@ def __repr__(self) -> str:
     def is_valid_value(self, value: float | npt.NDArray[float]) -> bool:
         return True
 
+    @override
+    def copy(self) -> Node:
+        return ContinuousRandomVariableNode(
+            shape=self.shape, label=self.label, compute=self._compute
+        )
+
 
 class DiscreteRandomVariableNode(RandomVariableNode):
     """A node containing a discrete random variable (RV)."""
@@ -112,7 +117,7 @@ def __init__(
         Args:
             shape: The shape of the output of the RV
             label: A unique label to identify the node
-            compute: A function to compute this node's value from given values of its parent nodes
+            compute: A function to compute node's value from given values of parents
 
         """
         super().__init__(label=label, shape=shape, compute=compute)
@@ -133,3 +138,12 @@ def is_valid_value(self, value: float | npt.NDArray[float]) -> bool:
             if np.allclose(v, value):
                 return True
         return False
+
+    @override
+    def copy(self) -> Node:
+        return DiscreteRandomVariableNode(
+            values=self._values,
+            shape=self.shape,
+            label=self.label,
+            compute=self._compute,
+        )
diff --git a/tests/test_graph/test_random_variables.py b/tests/test_node/test_random_variables.py
similarity index 73%
rename from tests/test_graph/test_random_variables.py
rename to tests/test_node/test_random_variables.py
index e2fabd3..0f87d96 100644
--- a/tests/test_graph/test_random_variables.py
+++ b/tests/test_node/test_random_variables.py
@@ -28,8 +28,8 @@ def test_invalid_discrete_node_value(raises_context):
 def test_sum_parents():
     graph = Graph(label="G")
 
-    graph.add_node(ContinuousRandomVariableNode(label="X"))
-    graph.add_node(DiscreteRandomVariableNode(label="Y", values=[-0.5, 0.0, 0.5]))
-    graph.add_node(ContinuousRandomVariableNode(label="Z", compute=lambda X, Y: X + Y))
+    graph.add_node(ContinuousRandomVariableNode(label="x"))
+    graph.add_node(DiscreteRandomVariableNode(label="y", values=[-0.5, 0.0, 0.5]))
+    graph.add_node(ContinuousRandomVariableNode(label="z", compute=lambda x, y: x + y))
 
-    assert np.isclose(graph.get_node("Z").evaluate(X=3.0, Y=-0.5), 2.5)
+    assert np.isclose(graph.get_node("z").evaluate(x=3.0, y=-0.5), 2.5)
diff --git a/tests/test_node/test_vector_nodes.py b/tests/test_node/test_vector_nodes.py
index 39230ef..44e848e 100644
--- a/tests/test_node/test_vector_nodes.py
+++ b/tests/test_node/test_vector_nodes.py
@@ -45,6 +45,6 @@ def test_get_component_node(rng_key):
     assert s0.shape == (100, 5)
     assert node[:, 1].sample({}, {"X": s}, 100, rng_key=rng_key).shape == (100, 4)
     assert node[0, 1].sample({}, {"X": s}, 100, rng_key=rng_key).shape == (100,)
-    assert node[0][1].sample({}, {"X": s, "X[0]": s0}, 100, rng_key=rng_key).shape == (
+    assert node[0][1].sample({}, {"X": s, "X_0": s0}, 100, rng_key=rng_key).shape == (
         100,
     )

From 13ad54756635e40d6d5ebd6085ac08fa5f8518e0 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Thu, 25 Jun 2026 14:46:25 +0100
Subject: [PATCH 27/30] ruff

---
 src/causalprog/graph/node/random_variables.py | 7 ++-----
 tests/test__abc/test_labelled.py              | 2 +-
 2 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/src/causalprog/graph/node/random_variables.py b/src/causalprog/graph/node/random_variables.py
index 79fd619..81e8b06 100644
--- a/src/causalprog/graph/node/random_variables.py
+++ b/src/causalprog/graph/node/random_variables.py
@@ -78,7 +78,7 @@ def parents(self) -> list[str]:
         return self._parents
 
     @abstractmethod
-    def is_valid_value(self, value: float | npt.NDArray[float]):
+    def is_valid_value(self, value: float | npt.NDArray[float]) -> bool:
         """Check if a value is valid for this node."""
 
 
@@ -134,10 +134,7 @@ def __repr__(self) -> str:
 
     @override
     def is_valid_value(self, value: float | npt.NDArray[float]) -> bool:
-        for v in self._values:
-            if np.allclose(v, value):
-                return True
-        return False
+        return any(np.allclose(v, value) for v in self._values)
 
     @override
     def copy(self) -> Node:
diff --git a/tests/test__abc/test_labelled.py b/tests/test__abc/test_labelled.py
index 6d53372..3f17704 100644
--- a/tests/test__abc/test_labelled.py
+++ b/tests/test__abc/test_labelled.py
@@ -32,5 +32,5 @@ def test_invalid_label(label, raises_context):
         "_a",
     ],
 )
-def test_valid_label(label, raises_context):
+def test_valid_label(label):
     Labelled(label=label)

From f548150682274e13d8a43d0c3366d14f1f5eb283 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Fri, 26 Jun 2026 14:01:15 +0100
Subject: [PATCH 28/30] add assert_is_valid_value

---
 src/causalprog/graph/node/random_variables.py | 22 +++++++++++--------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/src/causalprog/graph/node/random_variables.py b/src/causalprog/graph/node/random_variables.py
index 81e8b06..a79ba3f 100644
--- a/src/causalprog/graph/node/random_variables.py
+++ b/src/causalprog/graph/node/random_variables.py
@@ -56,15 +56,7 @@ def evaluate(
     ) -> float | npt.NDArray[float]:
         if self.label in given_values:
             value = given_values[self.label]
-            if not self.is_valid_value(value):
-                msg = (
-                    f"Invalid value for {self.__class__.__name__}: "
-                    f"{self.label} cannot be {value}"
-                )
-                raise ValueError(msg)
-            if self.shape != (value.shape if hasattr(value, "shape") else ()):
-                msg = f"Invalid value for node: {self.label}"
-                raise ValueError(msg)
+            self.assert_is_valid_value(value)
             return value
 
         if self._compute is None:
@@ -81,6 +73,18 @@ def parents(self) -> list[str]:
     def is_valid_value(self, value: float | npt.NDArray[float]) -> bool:
         """Check if a value is valid for this node."""
 
+    def assert_is_valid_value(self, value: float | npt.NDArray[float]):
+        """Check if a value is valid for this node."""
+        if not self.is_valid_value(value):
+            msg = (
+                f"Invalid value for {self.__class__.__name__}: "
+                f"{self.label} cannot be {value}"
+            )
+            raise ValueError(msg)
+        if self.shape != (value.shape if hasattr(value, "shape") else ()):
+            msg = f"Invalid value for node: {self.label}"
+            raise ValueError(msg)
+
 
 class ContinuousRandomVariableNode(RandomVariableNode):
     """A node containing a continuous random variable (RV)."""

From fb9c13cb1756e873c61fe49c3a1c3d8adbf09c62 Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Fri, 26 Jun 2026 14:04:04 +0100
Subject: [PATCH 29/30] Update tests/test_node/test_random_variables.py

Co-authored-by: Will Graham <32364977+willGraham01@users.noreply.github.com>
---
 tests/test_node/test_random_variables.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_node/test_random_variables.py b/tests/test_node/test_random_variables.py
index 0f87d96..3905806 100644
--- a/tests/test_node/test_random_variables.py
+++ b/tests/test_node/test_random_variables.py
@@ -25,7 +25,7 @@ def test_invalid_discrete_node_value(raises_context):
         node.evaluate(Y=-1.0)
 
 
-def test_sum_parents():
+def test_evaluate_down_graph():
     graph = Graph(label="G")
 
     graph.add_node(ContinuousRandomVariableNode(label="x"))

From 7a0104cb944414c17173aeb00d8c4717c02657ec Mon Sep 17 00:00:00 2001
From: Matthew Scroggs <matthew.w.scroggs@gmail.com>
Date: Fri, 26 Jun 2026 14:06:27 +0100
Subject: [PATCH 30/30] -> None

---
 src/causalprog/graph/node/random_variables.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/causalprog/graph/node/random_variables.py b/src/causalprog/graph/node/random_variables.py
index a79ba3f..9f5dd38 100644
--- a/src/causalprog/graph/node/random_variables.py
+++ b/src/causalprog/graph/node/random_variables.py
@@ -73,7 +73,7 @@ def parents(self) -> list[str]:
     def is_valid_value(self, value: float | npt.NDArray[float]) -> bool:
         """Check if a value is valid for this node."""
 
-    def assert_is_valid_value(self, value: float | npt.NDArray[float]):
+    def assert_is_valid_value(self, value: float | npt.NDArray[float]) -> None:
         """Check if a value is valid for this node."""
         if not self.is_valid_value(value):
             msg = (