Updated Mastermind.

mastermind/src/mastermind/Main.java

@@ -361,16 +361,17 @@ class Game extends World {
     public Game onKeyEvent(String key) {
         if ("123456789".contains(key)) { // User has entered a number.
             int choice = Integer.valueOf(key);
-            return this.addDot(choice - 1);
-            //} else if (key.equals("backspace")) {
-            //return this.dropDot();
+            if (choice <= this.conf.options.len()) return this.addDot(
+                    choice - 1
+                );
+        } else if (key.equals("backspace")) {
+            return this.dropDot();
         }
         return this;
     }
 
     // Attempt to add the nth dot option to the incomplete guess.
     Game addDot(int choice) {
-        System.out.println("tying to ");
         return new Game(
             this.conf,
             this.solution,
@@ -384,8 +385,17 @@ class Game extends World {
         );
     }
 
-    // Attempt to remove the last dot from the incomplete guess.
-    //Game dropDot() {}
+    // Attempt to remove the last dot in the incomplete guess.
+    Game dropDot() {
+        return new Game(
+            this.conf,
+            this.solution,
+            this.guessesLeft,
+            this.guesses.dropFromIncomplete(),
+            this.won,
+            this.done
+        );
+    }
 
     // Calculate the width of the window without drawing anything.
     int calcW() {
@@ -479,6 +489,7 @@ class GameConf {
 interface ILoGuess {
     WorldImage draw();
     ILoGuess addToIncomplete(Dot dot, int limit);
+    ILoGuess dropFromIncomplete();
 }
 
 class ConsGuess implements ILoGuess {
@@ -496,7 +507,11 @@ class ConsGuess implements ILoGuess {
     }
 
     public ILoGuess addToIncomplete(Dot dot, int limit) {
-        return this.nxt.addToIncomplete(dot, limit);
+        return new ConsGuess(this.guess, this.nxt.addToIncomplete(dot, limit));
+    }
+
+    public ILoGuess dropFromIncomplete() {
+        return new ConsGuess(this.guess, this.nxt.dropFromIncomplete());
     }
 }
 
@@ -515,15 +530,17 @@ class ConsIncompleteGuess implements ILoGuess {
     }
 
     public ILoGuess addToIncomplete(Dot dot, int limit) {
-        System.out.println("Here");
         return new ConsIncompleteGuess(
-            new IncompleteGuess(new ConsDot(dot, new MtDot())),
+            this.guessSoFar.tryAppend(dot, limit),
+            this.nxt
+        );
+    }
+
+    public ILoGuess dropFromIncomplete() {
+        return new ConsIncompleteGuess(
+            this.guessSoFar.tryRemoveLast(),
             this.nxt
         );
-        // return new ConsIncompleteGuess(
-        //     this.guessSoFar.tryAppend(dot, limit),
-        //     this.nxt
-        // );
     }
 }
 
@@ -555,6 +572,10 @@ class ConsPlaceholderGuess implements ILoGuess {
     public ILoGuess addToIncomplete(Dot dot, int limit) {
         return new ConsPlaceholderGuess(this.nxt.addToIncomplete(dot, limit));
     }
+
+    public ILoGuess dropFromIncomplete() {
+        return new ConsPlaceholderGuess(this.nxt.dropFromIncomplete());
+    }
 }
 
 class MtGuess implements ILoGuess {
@@ -566,6 +587,10 @@ class MtGuess implements ILoGuess {
     public ILoGuess addToIncomplete(Dot dot, int limit) {
         return this;
     }
+
+    public ILoGuess dropFromIncomplete() {
+        return this;
+    }
 }
 
 // A guess.
@@ -604,6 +629,13 @@ class IncompleteGuess {
         );
         else return this;
     }
+
+    //Remove the last dot.
+    IncompleteGuess tryRemoveLast() {
+        int len = this.guessSoFar.len();
+        if (len == 0) return this;
+        else return new IncompleteGuess(this.guessSoFar.remove(len - 1));
+    }
 }
 
 // Feedback for a guess.