Switch the Lexer and TreeBuilder to using exceptions.

core/src/main/java/org/nwapw/abacus/exception/TokenizeException.java

@@ -0,0 +1,23 @@
+package org.nwapw.abacus.exception;
+
+/**
+ * Exception thrown by Lexers when they are unable to tokenize the input string.
+ */
+public class TokenizeException extends AbacusException {
+
+    /**
+     * Create a new tokenize exception with no additional data.
+     */
+    public TokenizeException() {
+        this("");
+    }
+
+    /**
+     * Create a new tokenize exception with the given message.
+     * @param message the message to use.
+     */
+    public TokenizeException(String message){
+        super("Failed to tokenize string", message);
+    }
+
+}

core/src/main/java/org/nwapw/abacus/parsing/LexerTokenizer.java

@@ -1,5 +1,6 @@
 package org.nwapw.abacus.parsing;
 
+import org.nwapw.abacus.exception.TokenizeException;
 import org.nwapw.abacus.lexing.Lexer;
 import org.nwapw.abacus.lexing.pattern.Match;
 import org.nwapw.abacus.lexing.pattern.Pattern;
@@ -42,7 +43,9 @@ public class LexerTokenizer implements Tokenizer<Match<TokenType>>, PluginListen
 
     @Override
     public List<Match<TokenType>> tokenizeString(String string) {
-        return lexer.lexAll(string, 0, TOKEN_SORTER);
+        List<Match<TokenType>> tokens = lexer.lexAll(string, 0, TOKEN_SORTER);
+        if(tokens == null) throw new TokenizeException();
+        return tokens;
     }
 
     @Override

core/src/main/java/org/nwapw/abacus/parsing/TreeBuilder.java

@@ -42,9 +42,7 @@ public class TreeBuilder<T> {
      * @return the resulting tree.
      */
     public TreeNode fromString(String input) {
-        List<T> tokens = tokenizer.tokenizeString(input);
+        return parser.constructTree(tokenizer.tokenizeString(input));
-        if (tokens == null) return null;
-        return parser.constructTree(tokens);
     }
 
 }

core/src/main/kotlin/org/nwapw/abacus/Abacus.kt

@@ -88,7 +88,7 @@ class Abacus(val configuration: Configuration) {
      * @param input the input string to parse
      * @return the resulting tree, null if the tree builder or the produced tree are null.
      */
-    fun parseString(input: String): TreeNode? = treeBuilder.fromString(input)
+    fun parseString(input: String): TreeNode = treeBuilder.fromString(input)
     /**
      * Evaluates the given tree.
      *

core/src/test/java/org/nwapw/abacus/tests/CalculationTests.java

@@ -22,7 +22,6 @@ public class CalculationTests {
 
     private void testOutput(String input, String parseOutput, String output) {
         TreeNode parsedTree = abacus.parseString(input);
-        Assert.assertNotNull(parsedTree);
         Assert.assertEquals(parsedTree.toString(), parseOutput);
         NumberInterface result = abacus.evaluateTree(parsedTree).getValue();
         Assert.assertNotNull(result);
@@ -31,7 +30,6 @@ public class CalculationTests {
 
     private void testDomainException(String input, String parseOutput) {
         TreeNode parsedTree = abacus.parseString(input);
-        Assert.assertNotNull(parsedTree);
         Assert.assertEquals(parsedTree.toString(), parseOutput);
         try {
             abacus.evaluateTree(parsedTree);

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

@@ -142,9 +142,6 @@ public class AbacusController implements PluginListener {
         private String attemptCalculation() {
             try {
                 TreeNode constructedTree = abacus.parseString(inputField.getText());
-                if (constructedTree == null) {
-                    return ERR_SYNTAX;
-                }
                 EvaluationResult result = abacus.evaluateTree(constructedTree);
                 NumberInterface evaluatedNumber = result.getValue();
                 String resultingString = evaluatedNumber.toString();