Move the code for applicables that require a Reducer.

core/src/main/java/org/nwapw/abacus/function/ReducerApplicable.java

@@ -0,0 +1,44 @@
+package org.nwapw.abacus.function;
+
+import org.nwapw.abacus.tree.Reducer;
+
+/**
+ * A slightly more specific Applicable that requires a reducer
+ * to be passed to it along with the parameters.
+ * @param <T> the type of the input arguments.
+ * @param <O> the return type of the application.
+ * @param <R> the required type of the reducer.
+ */
+public abstract class ReducerApplicable<T, O, R> extends Applicable<T, O> {
+
+    @Override
+    protected final O applyInternal(T[] params) {
+        return null;
+    }
+
+    @Override
+    public final O apply(T... params) {
+        return null;
+    }
+
+    /**
+     * Applies this applicable to the given arguments, and reducer.
+     * @param reducer the reducer to use in the application.
+     * @param args the arguments to apply to.
+     * @return the result of the application.
+     */
+    public abstract O applyWithReducerInternal(Reducer<R> reducer, T[] args);
+
+    /**
+     * Applies this applicable to the given arguments, and reducer,
+     * if the arguments and reducer are compatible with this applicable.
+     * @param reducer the reducer to use in the application.
+     * @param args the arguments to apply to.
+     * @return the result of the application, or null if the arguments are incompatible.
+     */
+    public O applyWithReducer(Reducer<R> reducer, T...args) {
+        if(!matchesParams(args) || reducer == null) return null;
+        return applyWithReducerInternal(reducer, args);
+    }
+
+}

core/src/main/java/org/nwapw/abacus/function/TreeValueFunction.java

@@ -1,43 +0,0 @@
-package org.nwapw.abacus.function;
-
-import org.nwapw.abacus.number.NumberInterface;
-import org.nwapw.abacus.tree.Reducer;
-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> {
-
-    @Override
-    protected NumberInterface applyInternal(TreeNode[] params) {
-        return null;
-    }
-
-    @Override
-    public NumberInterface apply(TreeNode... params) {
-        return null;
-    }
-
-    /**
-     * Applies the tree value functions to the given tree nodes,
-     * using the given reducer.
-     * @param reducer the reducer to use.
-     * @param params the parameters to apply to.
-     * @return the result of the application.
-     */
-    public abstract NumberInterface applyWithReducerInternal(Reducer<NumberInterface> reducer, TreeNode[] params);
-
-    /**
-     * Checks if the given parameters and reducer can be used
-     * with this function, and if so, calls the function on them.
-     * @param reducer the reducer to use.
-     * @param params the parameters to apply to.
-     * @return the result of the application, or null if the parameters are incompatible.
-     */
-    public NumberInterface applyWithReducer(Reducer<NumberInterface> reducer, TreeNode... params) {
-        if(!matchesParams(params) || reducer == null) return null;
-        return applyWithReducerInternal(reducer, params);
-    }
-}

core/src/main/kotlin/org/nwapw/abacus/function/TreeValueFunction.kt

@@ -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 trees.
+ *
+ * A function that operates on parse tree nodes instead of on already simplified numbers.
+ * Despite this, it returns a number, not a tree.
+ */
+abstract class TreeValueFunction : ReducerApplicable<TreeNode, NumberInterface, NumberInterface>()