Merge pull request #11 from Mond1c/development

improve errors

src/main/java/org/linalg/Main.java

@@ -8,7 +8,9 @@
 
 public class Main {
     public static void main(String[] args) {
-        try (final Scanner scanner = new Scanner(System.in)) {
+        Scanner scanner = null;
+        try {
+            scanner = new Scanner(System.in);
             String request = scanner.nextLine();
             if (request.contains(" at ")) {
                 String[] parts = request.split("at");
@@ -27,8 +29,10 @@ public static void main(String[] args) {
             } else {
                 System.out.println(new Parser().parse(request).evaluate().simplify().toLatexString());
             }
-        } catch (RuntimeException e) {
-            System.out.println(e.getMessage());
+        } catch (Exception e) {
+            System.out.println("Exception: " + e.getMessage());
+        } finally {
+            scanner.close();
         }
     }
 }

src/main/java/org/linalg/expression/parser/BaseParser.java

@@ -1,5 +1,7 @@
 package org.linalg.expression.parser;
 
+import org.linalg.expression.parser.exceptions.ParserException;
+
 public class BaseParser {
     private static final char END = '\0';
     private StringSource source;
@@ -75,7 +77,7 @@ protected void skipWhitespaces() {
         }
     }
 
-    protected IllegalArgumentException error(final String message) {
+    protected RuntimeException error(final String message) {
         return source.error(message);
     }
 

src/main/java/org/linalg/expression/parser/Parser.java

@@ -3,6 +3,7 @@
 
 import org.linalg.expression.PartOfExpression;
 import org.linalg.expression.operations.*;
+import org.linalg.expression.parser.exceptions.ParserException;
 import org.linalg.expression.parts.Const;
 import org.linalg.expression.parts.Matrix;
 import org.linalg.expression.parts.Variable;

src/main/java/org/linalg/expression/parser/StringSource.java

@@ -1,5 +1,7 @@
 package org.linalg.expression.parser;
 
+import org.linalg.expression.parser.exceptions.ParserException;
+
 public class StringSource {
     private final String data;
     private int pos;
@@ -28,7 +30,7 @@ public char cur() {
         return data.charAt(pos);
     }
 
-    public IllegalArgumentException error(final String message) {
-        return new IllegalArgumentException(pos + ": " + message);
+    public RuntimeException error(final String message) {
+        return new ParserException(data, pos, message);
     }
 }

src/main/java/org/linalg/expression/parser/exceptions/ParserException.java

@@ -0,0 +1,9 @@
+package org.linalg.expression.parser.exceptions;
+
+public class ParserException extends RuntimeException {
+    public ParserException(String expression, int pos, String message) {
+        super(message + ": " + expression.substring(Math.max(0, pos - 11), pos - 1)
+                + " --> " + expression.charAt(pos - 1) + " <-- "
+                + (pos < expression.length() ? expression.substring(pos, Math.min(pos + 10, expression.length())) : ""));
+    }
+}