diff --git a/core/src/main/java/org/nwapw/abacus/function/TreeValueFunction.java b/core/src/main/java/org/nwapw/abacus/function/TreeValueFunction.java
new file mode 100644
index 0000000..cd802c4
--- /dev/null
+++ b/core/src/main/java/org/nwapw/abacus/function/TreeValueFunction.java
@@ -0,0 +1,12 @@
+package org.nwapw.abacus.function;
+
+import org.nwapw.abacus.number.NumberInterface;
+import org.nwapw.abacus.tree.TreeNode;
+
+/**
+ * A function that operates on parse tree nodes instead of on already simplified numbers.
+ * Despite this, it returns a number, not a tree.
+ */
+public abstract class TreeValueFunction extends Applicable<TreeNode, NumberInterface> {
+
+}