Add defaults that actually work.

src/main/java/org/nwapw/abacus/Abacus.java

@@ -57,7 +57,7 @@ public class Abacus {
      * Creates a new instance of the Abacus calculator.
      */
     public Abacus() {
-        pluginManager = new PluginManager();
+        pluginManager = new PluginManager(this);
         numberReducer = new NumberReducer(this);
         configuration = new Configuration(CONFIG_FILE);
         configuration.saveTo(CONFIG_FILE);

src/main/java/org/nwapw/abacus/config/Configuration.java

@@ -5,6 +5,9 @@ import com.moandjiezana.toml.TomlWriter;
 
 import java.io.File;
 import java.io.IOException;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
 
 /**
  * The configuration object that stores
@@ -12,26 +15,38 @@ import java.io.IOException;
  */
 public class Configuration {
 
+    /**
+     * The defaults TOML string.
+     */
+    private static final String DEFAULT_CONFIG =
+            "numberImplementation = \"naive\"\n" +
+            "disabledPlugins = []";
+    /**
+     * The defaults TOML object, parsed from the string.
+     */
+    private static final Toml DEFAULT_TOML = new Toml().read(DEFAULT_CONFIG);
     /**
      * The TOML writer used to write this configuration to a file.
      */
     private static final TomlWriter TOML_WRITER = new TomlWriter();
-    /**
-     * The TOML reader used to load this config from a file.
-     */
-    private static final Toml TOML_READER = new Toml();
 
     /**
      * The implementation of the number that should be used.
      */
-    private String numberImplementation = "naive";
+    private String numberImplementation = "<default>";
+    /**
+     * The list of disabled plugins in this Configuration.
+     */
+    private Set<String> disabledPlugins = new HashSet<>();
 
     /**
      * Creates a new configuration with the given values.
      * @param numberImplementation the number implementation, like "naive" or "precise"
+     * @param disabledPlugins the list of disabled plugins.
      */
-    public Configuration(String numberImplementation){
+    public Configuration(String numberImplementation, String[] disabledPlugins){
         this.numberImplementation = numberImplementation;
+        this.disabledPlugins.addAll(Arrays.asList(disabledPlugins));
     }
 
     /**
@@ -40,7 +55,7 @@ public class Configuration {
      */
     public Configuration(File fromFile){
         if(!fromFile.exists()) return;
-        copyFrom(TOML_READER.read(fromFile).to(Configuration.class));
+        copyFrom(new Toml(DEFAULT_TOML).read(fromFile).to(Configuration.class));
     }
 
     /**
@@ -49,6 +64,7 @@ public class Configuration {
      */
     public void copyFrom(Configuration otherConfiguration){
         this.numberImplementation = otherConfiguration.numberImplementation;
+        this.disabledPlugins.addAll(otherConfiguration.disabledPlugins);
     }
 
     /**
@@ -80,4 +96,13 @@ public class Configuration {
     public void setNumberImplementation(String numberImplementation) {
         this.numberImplementation = numberImplementation;
     }
+
+    /**
+     * Gets the list of disabled plugins.
+     * @return the list of disabled plugins.
+     */
+    public Set<String> getDisabledPlugins() {
+        return disabledPlugins;
+    }
+
 }

src/main/java/org/nwapw/abacus/function/OperatorType.java

@@ -4,5 +4,5 @@ package org.nwapw.abacus.function;
  * The type of an operator, describing how it should behave.
  */
 public enum OperatorType {
-    BINARY_INFIX, UNARY_POSTFIX
+    BINARY_INFIX, UNARY_POSTFIX, UNARY_PREFIX
 }

src/main/java/org/nwapw/abacus/fx/AbacusApplication.java

@@ -6,6 +6,10 @@ import javafx.scene.Parent;
 import javafx.scene.Scene;
 import javafx.stage.Stage;
 
+/**
+ * The main application class for JavaFX responsible for loading
+ * and displaying the fxml file.
+ */
 public class AbacusApplication extends Application {
 
     @Override

src/main/java/org/nwapw/abacus/fx/AbacusController.java

@@ -4,16 +4,33 @@ import javafx.collections.FXCollections;
 import javafx.collections.ObservableList;
 import javafx.fxml.FXML;
 import javafx.scene.control.*;
+import javafx.scene.control.cell.CheckBoxListCell;
 import javafx.scene.text.Text;
 import javafx.util.Callback;
+import javafx.util.StringConverter;
 import org.nwapw.abacus.Abacus;
+import org.nwapw.abacus.config.Configuration;
 import org.nwapw.abacus.number.NumberInterface;
+import org.nwapw.abacus.plugin.PluginListener;
+import org.nwapw.abacus.plugin.PluginManager;
 import org.nwapw.abacus.tree.TreeNode;
 
+import java.util.Set;
 
-public class AbacusController {
 
+/**
+ * The controller for the abacus FX UI, responsible
+ * for all the user interaction.
+ */
+public class AbacusController implements PluginListener {
+
+    /**
+     * Constant string that is displayed if the text could not be lexed or parsed.
+     */
     private static final String ERR_SYNTAX = "Syntax Error";
+    /**
+     * Constant string that is displayed if the tree could not be reduced.
+     */
     private static final String ERR_EVAL = "Evaluation Error";
 
     @FXML
@@ -32,28 +49,53 @@ public class AbacusController {
     private Button inputButton;
     @FXML
     private ComboBox<String> numberImplementationBox;
+    @FXML
+    private ListView<ToggleablePlugin> enabledPluginView;
 
+    /**
+     * The list of history entries, created by the users.
+     */
     private ObservableList<HistoryModel> historyData;
 
+    /**
+     * The abacus instance used for calculations and all
+     * other main processing code.
+     */
     private ObservableList<String> numberImplementationOptions;
 
+    /**
+     * The list of plugin objects that can be toggled on and off,
+     * and, when reloaded, get added to the plugin manager's black list.
+     */
+    private ObservableList<ToggleablePlugin> enabledPlugins;
+
     private Abacus abacus;
 
     @FXML
     public void initialize(){
         Callback<TableColumn<HistoryModel, String>, TableCell<HistoryModel, String>> cellFactory =
                 param -> new CopyableCell<>();
+        Callback<ListView<ToggleablePlugin>, ListCell<ToggleablePlugin>> pluginCellFactory =
+                param -> new CheckBoxListCell<>(ToggleablePlugin::enabledProperty, new StringConverter<ToggleablePlugin>() {
+                    @Override
+                    public String toString(ToggleablePlugin object) {
+                        return object.getClassName().substring(object.getClassName().lastIndexOf('.') + 1);
+                    }
+
+                    @Override
+                    public ToggleablePlugin fromString(String string) {
+                        return new ToggleablePlugin(true, string);
+                    }
+                });
 
         historyData = FXCollections.observableArrayList();
         historyTable.setItems(historyData);
         numberImplementationOptions = FXCollections.observableArrayList();
         numberImplementationBox.setItems(numberImplementationOptions);
-        numberImplementationBox.valueProperty().addListener((observable, oldValue, newValue)
-                -> {
-            abacus.getConfiguration().setNumberImplementation(newValue);
-            abacus.getConfiguration().saveTo(Abacus.CONFIG_FILE);
-        });
         historyTable.getSelectionModel().setCellSelectionEnabled(true);
+        enabledPlugins = FXCollections.observableArrayList();
+        enabledPluginView.setItems(enabledPlugins);
+        enabledPluginView.setCellFactory(pluginCellFactory);
         inputColumn.setCellFactory(cellFactory);
         inputColumn.setCellValueFactory(cell -> cell.getValue().inputProperty());
         parsedColumn.setCellFactory(cellFactory);
@@ -62,10 +104,8 @@ public class AbacusController {
         outputColumn.setCellValueFactory(cell -> cell.getValue().outputProperty());
 
         abacus = new Abacus();
-        numberImplementationOptions.addAll(abacus.getPluginManager().getAllNumbers());
-        String actualImplementation = abacus.getConfiguration().getNumberImplementation();
-        String toSelect = (numberImplementationOptions.contains(actualImplementation)) ? actualImplementation : "naive";
-        numberImplementationBox.getSelectionModel().select(toSelect);
+        abacus.getPluginManager().addListener(this);
+        abacus.getPluginManager().reload();
     }
 
     @FXML
@@ -90,4 +130,41 @@ public class AbacusController {
         inputField.setText("");
     }
 
+    @FXML
+    private void performReload(){
+        Configuration configuration = abacus.getConfiguration();
+        Set<String> disabledPlugins = configuration.getDisabledPlugins();
+        disabledPlugins.clear();
+        for(ToggleablePlugin pluginEntry : enabledPlugins){
+            if(!pluginEntry.isEnabled()) disabledPlugins.add(pluginEntry.getClassName());
+        }
+        abacus.getPluginManager().reload();
+    }
+
+    @FXML
+    private void performSave(){
+        Configuration configuration = abacus.getConfiguration();
+        configuration.setNumberImplementation(numberImplementationBox.getSelectionModel().getSelectedItem());
+        configuration.saveTo(Abacus.CONFIG_FILE);
+    }
+
+    @Override
+    public void onLoad(PluginManager manager) {
+        Configuration configuration = abacus.getConfiguration();
+        Set<String> disabledPlugins = configuration.getDisabledPlugins();
+        numberImplementationOptions.addAll(abacus.getPluginManager().getAllNumbers());
+        String actualImplementation = configuration.getNumberImplementation();
+        String toSelect = (numberImplementationOptions.contains(actualImplementation)) ? actualImplementation : "<default>";
+        numberImplementationBox.getSelectionModel().select(toSelect);
+        for(Class<?> pluginClass : abacus.getPluginManager().getLoadedPluginClasses()){
+            String fullName = pluginClass.getName();
+            enabledPlugins.add(new ToggleablePlugin(!disabledPlugins.contains(fullName), fullName));
+        }
+    }
+
+    @Override
+    public void onUnload(PluginManager manager) {
+        enabledPlugins.clear();
+        numberImplementationOptions.clear();
+    }
 }

src/main/java/org/nwapw/abacus/fx/CopyableCell.java

@@ -6,8 +6,17 @@ import javafx.scene.input.MouseEvent;
 import java.awt.*;
 import java.awt.datatransfer.StringSelection;
 
+/**
+ * A cell that copies its value to the clipboard
+ * when double clicked.
+ * @param <S> The type of the table view generic type.
+ * @param <T> The type of the value contained in the cell.
+ */
 public class CopyableCell<S, T> extends TableCell<S, T> {
 
+    /**
+     * Creates a new copyable cell.
+     */
     public CopyableCell(){
         addEventFilter(MouseEvent.MOUSE_CLICKED, event -> {
             if(event.getClickCount() == 2){

src/main/java/org/nwapw/abacus/fx/HistoryModel.java

@@ -3,12 +3,33 @@ package org.nwapw.abacus.fx;
 import javafx.beans.property.SimpleStringProperty;
 import javafx.beans.property.StringProperty;
 
+/**
+ * The data model used for storing history entries.
+ */
 public class HistoryModel {
 
+    /**
+     * The property used for displaying the column
+     * for the user input.
+     */
     private final StringProperty input;
+    /**
+     * The property used for displaying the column
+     * that contains the parsed input.
+     */
     private final StringProperty parsed;
+    /**
+     * The property used for displaying the column
+     * that contains the program output.
+     */
     private final StringProperty output;
 
+    /**
+     * Creates a new history model with the given variables.
+     * @param input the user input
+     * @param parsed the parsed input
+     * @param output the program output.
+     */
     public HistoryModel(String input, String parsed, String output){
         this.input = new SimpleStringProperty();
         this.parsed = new SimpleStringProperty();
@@ -18,23 +39,47 @@ public class HistoryModel {
         this.output.setValue(output);
     }
 
+    /**
+     * Gets the input property.
+     * @return the input property.
+     */
     public StringProperty inputProperty() {
         return input;
     }
+    /**
+     * Gets the input.
+     * @return the input.
+     */
     public String getInput() {
         return input.get();
     }
 
+    /**
+     * Gets the parsed input property.
+     * @return the parsed input property.
+     */
     public StringProperty parsedProperty() {
         return parsed;
     }
+    /**
+     * Gets the parsed input.
+     * @return the parsed input.
+     */
     public String getParsed() {
         return parsed.get();
     }
 
+    /**
+     * Gets the output property.
+     * @return the output property.
+     */
     public StringProperty outputProperty() {
         return output;
     }
+    /**
+     * Gets the program output.
+     * @return the output.
+     */
     public String getOutput() {
         return output.get();
     }

src/main/java/org/nwapw/abacus/fx/ToggleablePlugin.java

@@ -0,0 +1,29 @@
+package org.nwapw.abacus.fx;
+
+import javafx.beans.property.BooleanProperty;
+import javafx.beans.property.SimpleBooleanProperty;
+
+public class ToggleablePlugin {
+
+    private final BooleanProperty enabled;
+    private final String className;
+
+    public ToggleablePlugin(boolean enabled, String className){
+        this.enabled = new SimpleBooleanProperty();
+        this.enabled.setValue(enabled);
+        this.className = className;
+    }
+
+    public BooleanProperty enabledProperty() {
+        return enabled;
+    }
+
+    public boolean isEnabled() {
+        return enabled.get();
+    }
+
+    public String getClassName() {
+        return className;
+    }
+
+}

src/main/java/org/nwapw/abacus/number/PreciseNumber.java

@@ -1,9 +1,12 @@
 package org.nwapw.abacus.number;
 
 import java.math.BigDecimal;
-import java.math.MathContext;
 import java.math.RoundingMode;
 
+/**
+ * A number that uses a BigDecimal to store its value,
+ * leading to infinite possible precision.
+ */
 public class PreciseNumber implements NumberInterface {
 
     /**

src/main/java/org/nwapw/abacus/parsing/ShuntingYardParser.java

@@ -55,9 +55,12 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
     public List<Match<TokenType>> intoPostfix(List<Match<TokenType>> from) {
         ArrayList<Match<TokenType>> output = new ArrayList<>();
         Stack<Match<TokenType>> tokenStack = new Stack<>();
+        TokenType previousType;
+        TokenType matchType = null;
         while (!from.isEmpty()) {
             Match<TokenType> match = from.remove(0);
-            TokenType matchType = match.getType();
+            previousType = matchType;
+            matchType = match.getType();
             if (matchType == TokenType.NUM) {
                 output.add(match);
             } else if (matchType == TokenType.FUNCTION) {
@@ -74,7 +77,13 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
                     continue;
                 }
 
-                while (!tokenStack.empty()) {
+                if(tokenString.equals("-") && (previousType == null || previousType == TokenType.OP ||
+                        previousType == TokenType.OPEN_PARENTH)){
+                    from.add(0, new Match<>("`", TokenType.OP));
+                    continue;
+                }
+
+                while (!tokenStack.empty() && type == OperatorType.BINARY_INFIX) {
                     Match<TokenType> otherMatch = tokenStack.peek();
                     TokenType otherMatchType = otherMatch.getType();
                     if (!(otherMatchType == TokenType.OP || otherMatchType == TokenType.FUNCTION)) break;
@@ -103,8 +112,8 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
         }
         while (!tokenStack.empty()) {
             Match<TokenType> match = tokenStack.peek();
-            TokenType matchType = match.getType();
-            if (!(matchType == TokenType.OP || matchType == TokenType.FUNCTION)) return null;
+            TokenType newMatchType = match.getType();
+            if (!(newMatchType == TokenType.OP || newMatchType == TokenType.FUNCTION)) return null;
             output.add(tokenStack.pop());
         }
         return output;
@@ -127,11 +136,11 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
                 TreeNode right = constructRecursive(matches);
                 TreeNode left = constructRecursive(matches);
                 if (left == null || right == null) return null;
-                else return new BinaryInfixNode(operator, left, right);
+                else return new BinaryNode(operator, left, right);
             } else {
                 TreeNode applyTo = constructRecursive(matches);
                 if (applyTo == null) return null;
-                else return new UnaryPrefixNode(operator, applyTo);
+                else return new UnaryNode(operator, applyTo);
             }
         } else if (matchType == TokenType.NUM) {
             return new NumberNode(abacus.numberFromString(match.getContent()));

src/main/java/org/nwapw/abacus/plugin/PluginManager.java

@@ -1,5 +1,6 @@
 package org.nwapw.abacus.plugin;
 
+import org.nwapw.abacus.Abacus;
 import org.nwapw.abacus.function.Function;
 import org.nwapw.abacus.function.Operator;
 import org.nwapw.abacus.number.NumberInterface;
@@ -52,11 +53,17 @@ public class PluginManager {
      * The list of plugin listeners attached to this instance.
      */
     private Set<PluginListener> listeners;
+    /**
+     * The abacus instance used to access other
+     * components of the application.
+     */
+    private Abacus abacus;
 
     /**
      * Creates a new plugin manager.
      */
-    public PluginManager() {
+    public PluginManager(Abacus abacus) {
+        this.abacus = abacus;
         loadedPluginClasses = new HashSet<>();
         plugins = new HashSet<>();
         cachedFunctions = new HashMap<>();
@@ -160,8 +167,13 @@ public class PluginManager {
      * Loads all the plugins in the PluginManager.
      */
     public void load() {
-        for (Plugin plugin : plugins) plugin.enable();
+        Set<String> disabledPlugins = abacus.getConfiguration().getDisabledPlugins();
         for (Plugin plugin : plugins) {
+            if(disabledPlugins.contains(plugin.getClass().getName())) continue;
+            plugin.enable();
+        }
+        for (Plugin plugin : plugins) {
+            if(disabledPlugins.contains(plugin.getClass().getName())) continue;
             allFunctions.addAll(plugin.providedFunctions());
             allOperators.addAll(plugin.providedOperators());
             allNumbers.addAll(plugin.providedNumbers());
@@ -173,11 +185,18 @@ public class PluginManager {
      * Unloads all the plugins in the PluginManager.
      */
     public void unload() {
-        for (Plugin plugin : plugins) plugin.disable();
+        listeners.forEach(e -> e.onUnload(this));
+        Set<String> disabledPlugins = abacus.getConfiguration().getDisabledPlugins();
+        for (Plugin plugin : plugins) {
+            if(disabledPlugins.contains(plugin.getClass().getName())) continue;
+            plugin.disable();
+        }
+        cachedFunctions.clear();
+        cachedOperators.clear();
+        cachedNumbers.clear();
         allFunctions.clear();
         allOperators.clear();
         allNumbers.clear();
-        listeners.forEach(e -> e.onUnload(this));
     }
 
     /**
@@ -185,7 +204,7 @@ public class PluginManager {
      */
     public void reload() {
         unload();
-        reload();
+        load();
     }
 
     /**
@@ -233,4 +252,12 @@ public class PluginManager {
         listeners.remove(listener);
     }
 
+    /**
+     * Gets a list of all the plugin class files that have been
+     * added to the plugin manager.
+     * @return the list of all the added plugin classes.
+     */
+    public Set<Class<?>> getLoadedPluginClasses() {
+        return loadedPluginClasses;
+    }
 }

src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java

@@ -52,6 +52,20 @@ public class StandardPlugin extends Plugin {
             return params[0].subtract(params[1]);
         }
     });
+    /**
+     * The negation operator, -
+     */
+    public static final Operator OP_NEGATE = new Operator(OperatorAssociativity.LEFT, OperatorType.UNARY_PREFIX, 0, new Function() {
+        @Override
+        protected boolean matchesParams(NumberInterface[] params) {
+            return params.length == 1;
+        }
+
+        @Override
+        protected NumberInterface applyInternal(NumberInterface[] params) {
+            return params[0].negate();
+        }
+    });
     /**
      * The multiplication operator, *
      */
@@ -76,16 +90,12 @@ public class StandardPlugin extends Plugin {
     public static final Operator OP_DIVIDE = new Operator(OperatorAssociativity.LEFT, OperatorType.BINARY_INFIX, 1, new Function() {
         @Override
         protected boolean matchesParams(NumberInterface[] params) {
-            return params.length >= 1;
+            return params.length == 2;
         }
 
         @Override
         protected NumberInterface applyInternal(NumberInterface[] params) {
-            NumberInterface product = params[0];
-            for (int i = 1; i < params.length; i++) {
-                product = product.multiply(params[i]);
-            }
-            return product;
+            return params[0].divide(params[1]);
         }
     });
     /**
@@ -317,6 +327,7 @@ public class StandardPlugin extends Plugin {
 
         registerOperator("+", OP_ADD);
         registerOperator("-", OP_SUBTRACT);
+        registerOperator("`", OP_NEGATE);
         registerOperator("*", OP_MULTIPLY);
         registerOperator("/", OP_DIVIDE);
         registerOperator("^", OP_CARET);
@@ -335,7 +346,7 @@ public class StandardPlugin extends Plugin {
 
     public static NumberInterface factorial(Class<? extends NumberInterface> numberClass, int n){
         if(!factorialLists.containsKey(numberClass)){
-            factorialLists.put(numberClass, new ArrayList<NumberInterface>());
+            factorialLists.put(numberClass, new ArrayList<>());
             factorialLists.get(numberClass).add(NaiveNumber.ONE.promoteTo(numberClass));
             factorialLists.get(numberClass).add(NaiveNumber.ONE.promoteTo(numberClass));
         }

src/main/java/org/nwapw/abacus/tree/BinaryNode.java

@@ -3,7 +3,7 @@ package org.nwapw.abacus.tree;
 /**
  * A tree node that represents an operation being applied to two operands.
  */
-public class BinaryInfixNode extends TreeNode {
+public class BinaryNode extends TreeNode {
 
     /**
      * The operation being applied.
@@ -18,7 +18,7 @@ public class BinaryInfixNode extends TreeNode {
      */
     private TreeNode right;
 
-    private BinaryInfixNode() {
+    private BinaryNode() {
     }
 
     /**
@@ -27,7 +27,7 @@ public class BinaryInfixNode extends TreeNode {
      *
      * @param operation the operation.
      */
-    public BinaryInfixNode(String operation) {
+    public BinaryNode(String operation) {
         this(operation, null, null);
     }
 
@@ -39,7 +39,7 @@ public class BinaryInfixNode extends TreeNode {
      * @param left      the left node of the expression.
      * @param right     the right node of the expression.
      */
-    public BinaryInfixNode(String operation, TreeNode left, TreeNode right) {
+    public BinaryNode(String operation, TreeNode left, TreeNode right) {
         this.operation = operation;
         this.left = left;
         this.right = right;

src/main/java/org/nwapw/abacus/tree/NumberReducer.java

@@ -28,15 +28,15 @@ public class NumberReducer implements Reducer<NumberInterface> {
     public NumberInterface reduceNode(TreeNode node, Object... children) {
         if (node instanceof NumberNode) {
             return ((NumberNode) node).getNumber();
-        } else if (node instanceof BinaryInfixNode) {
+        } else if (node instanceof BinaryNode) {
             NumberInterface left = (NumberInterface) children[0];
             NumberInterface right = (NumberInterface) children[1];
-            Function function = abacus.getPluginManager().operatorFor(((BinaryInfixNode) node).getOperation()).getFunction();
+            Function function = abacus.getPluginManager().operatorFor(((BinaryNode) node).getOperation()).getFunction();
             if (function == null) return null;
             return function.apply(left, right);
-        } else if (node instanceof UnaryPrefixNode) {
+        } else if (node instanceof UnaryNode) {
             NumberInterface child = (NumberInterface) children[0];
-            Function functionn = abacus.getPluginManager().operatorFor(((UnaryPrefixNode) node).getOperation()).getFunction();
+            Function functionn = abacus.getPluginManager().operatorFor(((UnaryNode) node).getOperation()).getFunction();
             if (functionn == null) return null;
             return functionn.apply(child);
         } else if (node instanceof FunctionNode) {

src/main/java/org/nwapw/abacus/tree/UnaryNode.java

@@ -1,6 +1,6 @@
 package org.nwapw.abacus.tree;
 
-public class UnaryPrefixNode extends TreeNode {
+public class UnaryNode extends TreeNode {
 
     /**
      * The operation this node will apply.
@@ -16,7 +16,7 @@ public class UnaryPrefixNode extends TreeNode {
      *
      * @param operation the operation for this node.
      */
-    public UnaryPrefixNode(String operation) {
+    public UnaryNode(String operation) {
         this(operation, null);
     }
 
@@ -26,7 +26,7 @@ public class UnaryPrefixNode extends TreeNode {
      * @param operation the operation for this node.
      * @param applyTo   the node to apply the function to.
      */
-    public UnaryPrefixNode(String operation, TreeNode applyTo) {
+    public UnaryNode(String operation, TreeNode applyTo) {
         this.operation = operation;
         this.applyTo = applyTo;
     }

src/main/resources/abacus.fxml

@@ -46,6 +46,13 @@
                     <padding><Insets left="10" right="10" top="10" bottom="10"/></padding>
                     <Label text="Number Implementation" GridPane.columnIndex="0" GridPane.rowIndex="0"/>
                     <ComboBox fx:id="numberImplementationBox" GridPane.columnIndex="1" GridPane.rowIndex="0"/>
+                    <ListView fx:id="enabledPluginView"
+                              GridPane.rowIndex="1" GridPane.columnIndex="0"
+                              GridPane.columnSpan="2" maxHeight="100"/>
+                    <HBox GridPane.columnIndex="0" GridPane.columnSpan="2" GridPane.rowIndex="2" spacing="10">
+                        <Button text="Apply" onAction="#performSave"/>
+                        <Button text="Reload" onAction="#performReload"/>
+                    </HBox>
                 </GridPane>
             </Tab>
         </TabPane>