feat(language): node constants in rule actions

3 files changed, 51 insertions, 2 deletions

diff --git a/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/Action.java b/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/Action.java
index 0ce0c3a4..edcf9526 100644
--- a/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/Action.java
+++ b/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/Action.java
@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2023 The Refinery Authors <https://refinery.tools/>
+ * SPDX-FileCopyrightText: 2023-2024 The Refinery Authors <https://refinery.tools/>
  *
  * SPDX-License-Identifier: EPL-2.0
  */
@@ -67,7 +67,7 @@ public class Action {
                 var outputVariables = actionLiteral.getOutputVariables();
                 int size = outputVariables.size();
                 if (size == 0) {
-                        // Identity mappings use a {@code null} allocation to avoid iterating over the output tuple.
+                        // Empty mappings use a {@code null} allocation to avoid iterating over the output tuple.
                         return;
                 }
                 if (size >= 2 && new HashSet<>(outputVariables).size() != size) {
diff --git a/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/ActionLiterals.java b/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/ActionLiterals.java
index d06e2479..6bd5075b 100644
--- a/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/ActionLiterals.java
+++ b/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/ActionLiterals.java
@@ -16,6 +16,10 @@ public final class ActionLiterals {
                 throw new IllegalArgumentException("This is a static utility class and should not be instantiated directly");
         }
 
+        public static ConstantActionLiteral constant(NodeVariable variable, int nodeId) {
+                return new ConstantActionLiteral(variable, nodeId);
+        }
+
         public static <T> PutActionLiteral<T> put(Symbol<T> symbol, T value, NodeVariable... parameters) {
                 return new PutActionLiteral<>(symbol, value, List.of(parameters));
         }
diff --git a/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/ConstantActionLiteral.java b/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/ConstantActionLiteral.java
new file mode 100644
index 00000000..fecb2960
--- /dev/null
+++ b/subprojects/store-dse/src/main/java/tools/refinery/store/dse/transition/actions/ConstantActionLiteral.java
@@ -0,0 +1,45 @@
+/*
+ * SPDX-FileCopyrightText: 2024 The Refinery Authors <https://refinery.tools/>
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package tools.refinery.store.dse.transition.actions;
+
+import tools.refinery.logic.term.NodeVariable;
+import tools.refinery.store.model.Model;
+import tools.refinery.store.tuple.Tuple;
+
+import java.util.List;
+
+public class ConstantActionLiteral extends AbstractActionLiteral {
+        private final NodeVariable variable;
+        private final int nodeId;
+
+        public ConstantActionLiteral(NodeVariable variable, int nodeId) {
+                this.variable = variable;
+                this.nodeId = nodeId;
+        }
+
+        public NodeVariable getVariable() {
+                return variable;
+        }
+
+        public int getNodeId() {
+                return nodeId;
+        }
+
+        @Override
+        public List<NodeVariable> getInputVariables() {
+                return List.of();
+        }
+
+        @Override
+        public List<NodeVariable> getOutputVariables() {
+                return List.of(variable);
+        }
+
+        @Override
+        public BoundActionLiteral bindToModel(Model model) {
+                return ignoredTuple -> Tuple.of(nodeId);
+        }
+}