Merge branch 'stoppable-new'

# Conflicts:
#	src/main/java/org/nwapw/abacus/fx/AbacusController.java
#	src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java

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

@@ -1,5 +1,6 @@
 package org.nwapw.abacus.fx;
 
+import javafx.application.Platform;
 import javafx.collections.FXCollections;
 import javafx.collections.ObservableList;
 import javafx.fxml.FXML;
@@ -45,7 +46,10 @@ public class AbacusController implements PluginListener {
      * Constant string that is displayed if the tree could not be reduced.
      */
     private static final String ERR_EVAL = "Evaluation Error";
-
+    /**
+     * Constant string that is displayed if the calculations are stopped before they are done.
+     */
+    private static final String ERR_STOP = "Stopped";
     @FXML
     private TabPane coreTabPane;
     @FXML
@@ -83,6 +87,7 @@ public class AbacusController implements PluginListener {
     private ObservableList<String> numberImplementationOptions;
 
     /**
+<<<<<<< HEAD
      * The list of plugin objects that can be toggled on and off,
      * and, when reloaded, get added to the plugin manager's black list.
      */
@@ -92,6 +97,20 @@ public class AbacusController implements PluginListener {
      * The abacus instance used for changing the plugin configuration.
      */
     private Abacus abacus;
+    /**
+     * Thread used for calculating.
+     */
+    private Thread calcThread;
+
+    /**
+     * Checks whether the calculator is calculating.
+     */
+    private boolean calculating;
+
+    /**
+     * Seconds delayed for timer;
+     */
+    private double delay = 0;
 
     /**
      * Boolean which represents whether changes were made to the configuration.
@@ -167,25 +186,63 @@ public class AbacusController implements PluginListener {
     }
 
     @FXML
-    private void performCalculation() {
-        inputButton.setDisable(true);
-        TreeNode constructedTree = abacus.parseString(inputField.getText());
-        if (constructedTree == null) {
-            outputText.setText(ERR_SYNTAX);
-            inputButton.setDisable(false);
-            return;
-        }
-        NumberInterface evaluatedNumber = abacus.evaluateTree(constructedTree);
-        if (evaluatedNumber == null) {
-            outputText.setText(ERR_EVAL);
-            inputButton.setDisable(false);
-            return;
-        }
-        outputText.setText(evaluatedNumber.toString());
-        historyData.add(new HistoryModel(inputField.getText(), constructedTree.toString(), evaluatedNumber.toString()));
+    private void performCalculation(){
+        Runnable calculator = new Runnable(){
+            public void run() {
+                if(delay>0) {
+                    Runnable timer = new Runnable() {
+                        public void run() {
+                            long gap = (long) (delay * 1000);
+                            long startTime = System.currentTimeMillis();
+                            while (System.currentTimeMillis() - startTime <= gap) {
+                            }
+                            stopCalculation();
+                        }
+                    };
+                    Thread maxTime = new Thread(timer);
+                    maxTime.setName("maxTime");
+                    maxTime.start();
+                }
+                calculating = true;
+                Platform.runLater(() -> inputButton.setDisable(true));
+                TreeNode constructedTree = abacus.parseString(inputField.getText());
+                if (constructedTree == null) {
+                    Platform.runLater(() ->outputText.setText(ERR_SYNTAX));
+                    Platform.runLater(() -> inputButton.setDisable(false));
+                    //return;
+                }else {
+                    NumberInterface evaluatedNumber = abacus.evaluateTree(constructedTree);
+                    if (evaluatedNumber == null) {
+                        if(Thread.currentThread().isInterrupted()){
+                            Platform.runLater(() -> outputText.setText(ERR_STOP));
+                            Platform.runLater(() -> inputButton.setDisable(false));
+                        }else {
+                            Platform.runLater(() -> outputText.setText(ERR_EVAL));
+                            Platform.runLater(() -> inputButton.setDisable(false));
+                            //return;
+                        }
+                    } else {
+                        Platform.runLater(() -> outputText.setText(evaluatedNumber.toString()));
+                        historyData.add(new HistoryModel(inputField.getText(), constructedTree.toString(), evaluatedNumber.toString()));
 
-        inputButton.setDisable(false);
-        inputField.setText("");
+                        Platform.runLater(() -> inputButton.setDisable(false));
+                        Platform.runLater(() -> inputField.setText(""));
+                    }
+                }
+                calculating = false;
+            }
+        };
+        if(!calculating) {
+                calcThread = new Thread(calculator);
+                calcThread.setName("calcThread");
+                calcThread.start();
+        }
+    }
+    @FXML
+    private void stopCalculation(){
+        calcThread.interrupt();
+        calculating = false;
+        //Platform.runLater(() ->inputButton.setDisable(false));
     }
 
     @FXML

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

@@ -29,9 +29,13 @@ public class StandardPlugin extends Plugin {
 
         @Override
         protected NumberInterface applyInternal(NumberInterface[] params) {
+            if(Thread.currentThread().isInterrupted())
+                return null;
             NumberInterface sum = params[0];
             for (int i = 1; i < params.length; i++) {
                 sum = sum.add(params[i]);
+                if(Thread.currentThread().isInterrupted())
+                    return null;
             }
             return sum;
         }
@@ -47,7 +51,10 @@ public class StandardPlugin extends Plugin {
 
         @Override
         protected NumberInterface applyInternal(NumberInterface[] params) {
+            if(Thread.currentThread().isInterrupted())
+                return null;
             return params[0].subtract(params[1]);
+
         }
     });
     /**
@@ -61,6 +68,8 @@ public class StandardPlugin extends Plugin {
 
         @Override
         protected NumberInterface applyInternal(NumberInterface[] params) {
+            if(Thread.currentThread().isInterrupted())
+                return null;
             return params[0].negate();
         }
     });
@@ -75,9 +84,13 @@ public class StandardPlugin extends Plugin {
 
         @Override
         protected NumberInterface applyInternal(NumberInterface[] params) {
+            if(Thread.currentThread().isInterrupted())
+                return null;
             NumberInterface product = params[0];
             for (int i = 1; i < params.length; i++) {
                 product = product.multiply(params[i]);
+                if(Thread.currentThread().isInterrupted())
+                    return null;
             }
             return product;
         }
@@ -93,6 +106,8 @@ public class StandardPlugin extends Plugin {
 
         @Override
         protected NumberInterface applyInternal(NumberInterface[] params) {
+            if(Thread.currentThread().isInterrupted())
+                return null;
             return params[0].divide(params[1]);
         }
     });
@@ -110,15 +125,19 @@ public class StandardPlugin extends Plugin {
 
         @Override
         protected NumberInterface applyInternal(NumberInterface[] params) {
+            if(Thread.currentThread().isInterrupted())
+                return null;
             if (params[0].signum() == 0) {
                 return (new NaiveNumber(1)).promoteTo(params[0].getClass());
             }
             NumberInterface factorial = params[0];
             NumberInterface multiplier = params[0];
             //It is necessary to later prevent calls of factorial on anything but non-negative integers.
-            while ((multiplier = multiplier.subtract(NaiveNumber.ONE.promoteTo(multiplier.getClass()))).signum() == 1) {
+            while (!Thread.currentThread().isInterrupted()&&(multiplier = multiplier.subtract(NaiveNumber.ONE.promoteTo(multiplier.getClass())))!=null&&multiplier.signum() == 1) {
                 factorial = factorial.multiply(multiplier);
             }
+            if(Thread.currentThread().isInterrupted())
+                return null;
             return factorial;
                 /*if(!storedList.containsKey(params[0].getClass())){
                     storedList.put(params[0].getClass(), new ArrayList<NumberInterface>());
@@ -128,6 +147,32 @@ public class StandardPlugin extends Plugin {
         }
     });
     /**
+<<<<<<< HEAD
+=======
+     * The caret / pow operator, ^
+     */
+    public static final Operator OP_CARET = new Operator(OperatorAssociativity.RIGHT, OperatorType.BINARY_INFIX, 2, new Function() {
+        @Override
+        protected boolean matchesParams(NumberInterface[] params) {
+            return params.length == 2
+                    && !(params[0].compareTo(NaiveNumber.ZERO.promoteTo(params[0].getClass())) == 0
+                    && params[1].compareTo(NaiveNumber.ZERO.promoteTo(params[1].getClass())) == 0);
+        }
+
+        @Override
+        protected NumberInterface applyInternal(NumberInterface[] params) {
+            NumberInterface check;
+            if(Thread.currentThread().isInterrupted()) return null;
+            else if (params[0].compareTo(NaiveNumber.ZERO.promoteTo(params[0].getClass())) == 0)
+                return NaiveNumber.ZERO.promoteTo(params[0].getClass());
+            else if (params[1].compareTo(NaiveNumber.ZERO.promoteTo(params[0].getClass())) == 0)
+                return NaiveNumber.ONE.promoteTo(params[1].getClass());
+            if((check = FUNCTION_EXP.apply(FUNCTION_LN.apply(params[0])))!=null&&(check = check.multiply(params[1]))!=null)
+                return check;
+            return null;
+        }
+    });
+    /**
      * The absolute value function, abs(-3) = 3
      */
     public static final Function FUNCTION_ABS = new Function() {
@@ -138,9 +183,53 @@ public class StandardPlugin extends Plugin {
 
         @Override
         protected NumberInterface applyInternal(NumberInterface[] params) {
+            if(Thread.currentThread().isInterrupted())
+                return null;
             return params[0].multiply((new NaiveNumber(params[0].signum())).promoteTo(params[0].getClass()));
         }
     };
+    /**
+     * The exponential function, exp(1) = e^1 = 2.71...
+     */
+    public static final Function FUNCTION_EXP = new Function() {
+        @Override
+        protected boolean matchesParams(NumberInterface[] params) {
+            return params.length == 1;
+        }
+
+        @Override
+        protected NumberInterface applyInternal(NumberInterface[] params) {
+            NumberInterface maxError = getMaxError(params[0]);
+            int n = 0;
+            if (params[0].signum() <= 0) {
+                NumberInterface currentTerm = NaiveNumber.ONE.promoteTo(params[0].getClass()), sum = currentTerm;
+                while (FUNCTION_ABS.apply(currentTerm).compareTo(maxError) > 0) {
+                    n++;
+                    currentTerm = currentTerm.multiply(params[0]).divide((new NaiveNumber(n)).promoteTo(params[0].getClass()));
+                    sum = sum.add(currentTerm);
+                }
+                return sum;
+            } else {
+                //We need n such that x^(n+1) * 3^ceil(x) <= maxError * (n+1)!.
+                //right and left refer to lhs and rhs in the above inequality.
+                NumberInterface sum = NaiveNumber.ONE.promoteTo(params[0].getClass());
+                NumberInterface nextNumerator = params[0];
+                NumberInterface left = params[0].multiply((new NaiveNumber(3)).promoteTo(params[0].getClass()).intPow(params[0].ceiling().intValue())), right = maxError;
+                do {
+                    sum = sum.add(nextNumerator.divide(factorial(params[0].getClass(), n + 1)));
+                    n++;
+                    nextNumerator = nextNumerator.multiply(params[0]);
+                    left = left.multiply(params[0]);
+                    NumberInterface nextN = (new NaiveNumber(n + 1)).promoteTo(params[0].getClass());
+                    right = right.multiply(nextN);
+                    //System.out.println(left + ", " + right);
+                }
+                while (left.compareTo(right) > 0);
+                //System.out.println(n+1);
+                return sum;
+            }
+        }
+    };
     /**
      * The natural log function.
      */
@@ -152,26 +241,32 @@ public class StandardPlugin extends Plugin {
 
         @Override
         protected NumberInterface applyInternal(NumberInterface[] params) {
+            if(Thread.currentThread().isInterrupted())
+                return null;
             NumberInterface param = params[0];
             int powersOf2 = 0;
-            while (FUNCTION_ABS.apply(param.subtract(NaiveNumber.ONE.promoteTo(param.getClass()))).compareTo((new NaiveNumber(0.1)).promoteTo(param.getClass())) >= 0) {
-                if (param.subtract(NaiveNumber.ONE.promoteTo(param.getClass())).signum() == 1) {
+            NumberInterface check;
+            while (!Thread.currentThread().isInterrupted()&&(check = FUNCTION_ABS.apply(param.subtract(NaiveNumber.ONE.promoteTo(param.getClass()))))!=null&&(check.compareTo((new NaiveNumber(0.1)).promoteTo(param.getClass()))) >= 0) {
+                if ((check = param.subtract(NaiveNumber.ONE.promoteTo(param.getClass())))!=null&&check.signum() == 1) {
                     param = param.divide(new NaiveNumber(2).promoteTo(param.getClass()));
                     powersOf2++;
-                    if (param.subtract(NaiveNumber.ONE.promoteTo(param.getClass())).signum() != 1) {
+                    if ((check = param.subtract(NaiveNumber.ONE.promoteTo(param.getClass())))==null||check.signum() != 1) {
                         break;
                         //No infinite loop for you.
                     }
                 } else {
                     param = param.multiply(new NaiveNumber(2).promoteTo(param.getClass()));
                     powersOf2--;
-                    if (param.subtract(NaiveNumber.ONE.promoteTo(param.getClass())).signum() != -1) {
+                    if ((check = param.subtract(NaiveNumber.ONE.promoteTo(param.getClass())))==null||check.signum() != 1) {
                         break;
                         //No infinite loop for you.
                     }
                 }
             }
-            return getLog2(param).multiply((new NaiveNumber(powersOf2)).promoteTo(param.getClass())).add(getLogPartialSum(param));
+            NumberInterface check2;
+            if(!Thread.currentThread().isInterrupted()&&(check = getLog2(param))!=null&&(check = check.multiply((new NaiveNumber(powersOf2).promoteTo(param.getClass()))))!=null&&(check2 = getLogPartialSum(param))!=null&&(check = check.add(check2))!=null)
+                   return check;
+            return null;
         }
 
         /**
@@ -181,16 +276,23 @@ public class StandardPlugin extends Plugin {
          * @return the partial sum.
          */
         private NumberInterface getLogPartialSum(NumberInterface x) {
+
+            if(Thread.currentThread().isInterrupted())
+                return null;
             NumberInterface maxError = getMaxError(x);
             x = x.subtract(NaiveNumber.ONE.promoteTo(x.getClass())); //Terms used are for log(x+1).
             NumberInterface currentNumerator = x, currentTerm = x, sum = x;
             int n = 1;
-            while (FUNCTION_ABS.apply(currentTerm).compareTo(maxError) > 0) {
+            NumberInterface check;
+            while (!Thread.currentThread().isInterrupted()&&(check = FUNCTION_ABS.apply(currentTerm))!=null&&check.compareTo(maxError) > 0) {
                 n++;
-                currentNumerator = currentNumerator.multiply(x).negate();
+                if((currentNumerator = currentNumerator.multiply(x))==null||(currentNumerator = currentNumerator.negate())==null)
+                    return null;
                 currentTerm = currentNumerator.divide(new NaiveNumber(n).promoteTo(x.getClass()));
                 sum = sum.add(currentTerm);
             }
+            if(Thread.currentThread().isInterrupted())
+                return null;
             return sum;
         }
 
@@ -200,6 +302,8 @@ public class StandardPlugin extends Plugin {
          * @return the value of log(2) with the appropriate precision.
          */
         private NumberInterface getLog2(NumberInterface number) {
+            if(Thread.currentThread().isInterrupted())
+                return null;
             NumberInterface maxError = getMaxError(number);
             //NumberInterface errorBound = (new NaiveNumber(1)).promoteTo(number.getClass());
             //We'll use the series \sigma_{n >= 1) ((1/3^n + 1/4^n) * 1/n)
@@ -208,13 +312,17 @@ public class StandardPlugin extends Plugin {
             NumberInterface a = (new NaiveNumber(1)).promoteTo(number.getClass()), b = a, c = a;
             NumberInterface sum = NaiveNumber.ZERO.promoteTo(number.getClass());
             int n = 0;
-            while (a.compareTo(maxError) >= 1) {
+            while (!Thread.currentThread().isInterrupted()&&a.compareTo(maxError) >= 1) {
                 n++;
                 a = a.divide((new NaiveNumber(3)).promoteTo(number.getClass()));
                 b = b.divide((new NaiveNumber(4)).promoteTo(number.getClass()));
                 c = NaiveNumber.ONE.promoteTo(number.getClass()).divide((new NaiveNumber(n)).promoteTo(number.getClass()));
-                sum = sum.add(a.add(b).multiply(c));
+                NumberInterface check;
+                if(a==null||(check = a.add(b))==null||(check = check.multiply(c))==null||(sum = sum.add(check))==null)
+                    return null;
             }
+            if(Thread.currentThread().isInterrupted())
+                return null;
             return sum;
         }
     };
@@ -283,69 +391,6 @@ public class StandardPlugin extends Plugin {
         }
     };
     private static final HashMap<Class<? extends NumberInterface>, ArrayList<NumberInterface>> FACTORIAL_LISTS = new HashMap<>();
-    /**
-     * The exponential function, exp(1) = e^1 = 2.71...
-     */
-    public static final Function FUNCTION_EXP = new Function() {
-        @Override
-        protected boolean matchesParams(NumberInterface[] params) {
-            return params.length == 1;
-        }
-
-        @Override
-        protected NumberInterface applyInternal(NumberInterface[] params) {
-            NumberInterface maxError = getMaxError(params[0]);
-            int n = 0;
-            if (params[0].signum() <= 0) {
-                NumberInterface currentTerm = NaiveNumber.ONE.promoteTo(params[0].getClass()), sum = currentTerm;
-                while (FUNCTION_ABS.apply(currentTerm).compareTo(maxError) > 0) {
-                    n++;
-                    currentTerm = currentTerm.multiply(params[0]).divide((new NaiveNumber(n)).promoteTo(params[0].getClass()));
-                    sum = sum.add(currentTerm);
-                }
-                return sum;
-            } else {
-                //We need n such that x^(n+1) * 3^ceil(x) <= maxError * (n+1)!.
-                //right and left refer to lhs and rhs in the above inequality.
-                NumberInterface sum = NaiveNumber.ONE.promoteTo(params[0].getClass());
-                NumberInterface nextNumerator = params[0];
-                NumberInterface left = params[0].multiply((new NaiveNumber(3)).promoteTo(params[0].getClass()).intPow(params[0].ceiling().intValue())), right = maxError;
-                do {
-                    sum = sum.add(nextNumerator.divide(factorial(params[0].getClass(), n + 1)));
-                    n++;
-                    nextNumerator = nextNumerator.multiply(params[0]);
-                    left = left.multiply(params[0]);
-                    NumberInterface nextN = (new NaiveNumber(n + 1)).promoteTo(params[0].getClass());
-                    right = right.multiply(nextN);
-                    //System.out.println(left + ", " + right);
-                }
-                while (left.compareTo(right) > 0);
-                //System.out.println(n+1);
-                return sum;
-            }
-        }
-    };
-    /**
-     * The caret / pow operator, ^
-     */
-    public static final Operator OP_CARET = new Operator(OperatorAssociativity.RIGHT, OperatorType.BINARY_INFIX, 2, new Function() {
-        @Override
-        protected boolean matchesParams(NumberInterface[] params) {
-            return params.length == 2
-                    && !(params[0].compareTo(NaiveNumber.ZERO.promoteTo(params[0].getClass())) == 0
-                    && params[1].compareTo(NaiveNumber.ZERO.promoteTo(params[1].getClass())) == 0);
-        }
-
-        @Override
-        protected NumberInterface applyInternal(NumberInterface[] params) {
-            if (params[0].compareTo(NaiveNumber.ZERO.promoteTo(params[0].getClass())) == 0) {
-                return NaiveNumber.ZERO.promoteTo(params[0].getClass());
-            } else if (params[1].compareTo(NaiveNumber.ZERO.promoteTo(params[0].getClass())) == 0) {
-                return NaiveNumber.ONE.promoteTo(params[1].getClass());
-            }
-            return FUNCTION_EXP.apply(FUNCTION_LN.apply(FUNCTION_ABS.apply(params[0])).multiply(params[1]));
-        }
-    });
     /**
      * The sine function (the argument is interpreted in radians).
      */
@@ -480,18 +525,22 @@ public class StandardPlugin extends Plugin {
      * @param n           non-negative integer.
      * @return a number of numClass with value n factorial.
      */
-    public static NumberInterface factorial(Class<? extends NumberInterface> numberClass, int n) {
-        if (!FACTORIAL_LISTS.containsKey(numberClass)) {
+    public static NumberInterface factorial(Class<? extends NumberInterface> numberClass, int n){
+        if(Thread.currentThread().isInterrupted())
+            return null;
+        if(!FACTORIAL_LISTS.containsKey(numberClass)){
             FACTORIAL_LISTS.put(numberClass, new ArrayList<>());
             FACTORIAL_LISTS.get(numberClass).add(NaiveNumber.ONE.promoteTo(numberClass));
             FACTORIAL_LISTS.get(numberClass).add(NaiveNumber.ONE.promoteTo(numberClass));
         }
         ArrayList<NumberInterface> list = FACTORIAL_LISTS.get(numberClass);
-        if (n >= list.size()) {
-            while (list.size() < n + 16) {
-                list.add(list.get(list.size() - 1).multiply(new NaiveNumber(list.size()).promoteTo(numberClass)));
+        if(n >= list.size()){
+            while(!Thread.currentThread().isInterrupted()&&list.size() < n + 16){
+                list.add(list.get(list.size()-1).multiply(new NaiveNumber(list.size()).promoteTo(numberClass)));
             }
         }
+        if(Thread.currentThread().isInterrupted())
+            return null;
         return list.get(n);
     }
 
@@ -559,4 +608,26 @@ public class StandardPlugin extends Plugin {
     public void onDisable() {
 
     }
+
+    public static NumberInterface intPow(NumberInterface number, Class<? extends NumberInterface> numberClass,NumberInterface exponent) {
+        if(Thread.currentThread().isInterrupted())
+            return null;
+        if (exponent.compareTo((new NaiveNumber(0)).promoteTo(numberClass))==0) {
+            return (new NaiveNumber(1)).promoteTo(numberClass);
+        }
+        boolean takeReciprocal = exponent.compareTo((new NaiveNumber(0)).promoteTo(numberClass))<0;
+        exponent = FUNCTION_ABS.apply(exponent);
+        NumberInterface power = number;
+        for(NumberInterface currentExponent =(new NaiveNumber(1)).promoteTo(numberClass);currentExponent.compareTo(exponent)<0;currentExponent = currentExponent.add((new NaiveNumber(1)).promoteTo(numberClass))){
+            power = power.multiply(number);
+            if(Thread.currentThread().isInterrupted())
+                return null;
+        }
+        if (takeReciprocal) {
+            power = (new NaiveNumber(1)).promoteTo(numberClass).divide(power);
+        }
+        if(Thread.currentThread().isInterrupted())
+            return null;
+        return power;
+    }
 }

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

@@ -92,10 +92,15 @@ public class BinaryNode extends TreeNode {
 
     @Override
     public <T> T reduce(Reducer<T> reducer) {
+        if(Thread.currentThread().isInterrupted())
+            return null;
         T leftReduce = left.reduce(reducer);
         T rightReduce = right.reduce(reducer);
         if (leftReduce == null || rightReduce == null) return null;
-        return reducer.reduceNode(this, leftReduce, rightReduce);
+        T a = reducer.reduceNode(this, leftReduce, rightReduce);
+        if(Thread.currentThread().isInterrupted())
+            return null;
+        return a;
     }
 
     @Override

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

@@ -62,12 +62,17 @@ public class FunctionNode extends TreeNode {
 
     @Override
     public <T> T reduce(Reducer<T> reducer) {
+        if(Thread.currentThread().isInterrupted())
+            return null;
         Object[] reducedChildren = new Object[children.size()];
         for (int i = 0; i < reducedChildren.length; i++) {
             reducedChildren[i] = children.get(i).reduce(reducer);
-            if (reducedChildren[i] == null) return null;
+            if (Thread.currentThread().isInterrupted()||reducedChildren[i] == null) return null;
         }
-        return reducer.reduceNode(this, reducedChildren);
+        T a = reducer.reduceNode(this, reducedChildren);
+        if(Thread.currentThread().isInterrupted())
+            return null;
+        return a;
     }
 
     @Override

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

@@ -33,9 +33,14 @@ public class UnaryNode extends TreeNode {
 
     @Override
     public <T> T reduce(Reducer<T> reducer) {
+        if(Thread.currentThread().isInterrupted())
+            return null;
         Object reducedChild = applyTo.reduce(reducer);
         if (reducedChild == null) return null;
-        return reducer.reduceNode(this, reducedChild);
+        T a = reducer.reduceNode(this, reducedChild);
+        if(Thread.currentThread().isInterrupted())
+            return null;
+        return a;
     }
 
     /**

src/main/resources/abacus.fxml

@@ -38,6 +38,8 @@
                             <TextField fx:id="inputField" onAction="#performCalculation"/>
                             <Button fx:id="inputButton" text="Calculate" maxWidth="Infinity"
                                     onAction="#performCalculation"/>
+                            <Button fx:id="stopButton" text="Stop" maxWidth="Infinity"
+                                    onAction="#stopCalculation"/>
                         </VBox>
                     </bottom>
                 </BorderPane>