diff --git a/src b/src
deleted file mode 120000
index 075a5ba..0000000
--- a/src
+++ /dev/null
@@ -1 +0,0 @@
-/home/ondra/Dokumenty/EclipseWorkspace/RCalc/src
\ No newline at end of file
diff --git a/src/net/mightypork/rcalc/IDebugable.java b/src/net/mightypork/rcalc/IDebugable.java
new file mode 100644
index 0000000..2c737dc
--- /dev/null
+++ b/src/net/mightypork/rcalc/IDebugable.java
@@ -0,0 +1,26 @@
+package net.mightypork.rcalc;
+
+
+/**
+ * Interface for classes with optional debug mode
+ * 
+ * @author Ondrej Hruska
+ */
+public interface IDebugable {
+
+	/**
+	 * Get if debug mode is enabled
+	 * 
+	 * @return debug enabled
+	 */
+	public boolean isDebug();
+
+
+	/**
+	 * Enable / disable debug mode
+	 * 
+	 * @param debug enable debug
+	 */
+	public void setDebug(boolean debug);
+
+}
diff --git a/src/net/mightypork/rcalc/IEvaluable.java b/src/net/mightypork/rcalc/IEvaluable.java
new file mode 100644
index 0000000..b8ed8bd
--- /dev/null
+++ b/src/net/mightypork/rcalc/IEvaluable.java
@@ -0,0 +1,20 @@
+package net.mightypork.rcalc;
+
+
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Interface of an object that can be turned into a fractional value
+ * 
+ * @author Ondrej Hruska
+ */
+public interface IEvaluable {
+
+	/**
+	 * Get fractional value
+	 * 
+	 * @return fractional value
+	 */
+	public Fraction evaluate();
+}
diff --git a/src/net/mightypork/rcalc/IEvaluableToken.java b/src/net/mightypork/rcalc/IEvaluableToken.java
new file mode 100644
index 0000000..6f0f2d2
--- /dev/null
+++ b/src/net/mightypork/rcalc/IEvaluableToken.java
@@ -0,0 +1,11 @@
+package net.mightypork.rcalc;
+
+
+/**
+ * Evaluable token interface
+ * 
+ * @author Ondrej Hruska
+ */
+public interface IEvaluableToken extends IEvaluable, IToken {
+
+}
diff --git a/src/net/mightypork/rcalc/IToken.java b/src/net/mightypork/rcalc/IToken.java
new file mode 100644
index 0000000..54a28f1
--- /dev/null
+++ b/src/net/mightypork/rcalc/IToken.java
@@ -0,0 +1,11 @@
+package net.mightypork.rcalc;
+
+
+/**
+ * Token interface
+ * 
+ * @author Ondrej Hruska
+ */
+public interface IToken {
+
+}
diff --git a/src/net/mightypork/rcalc/ParseError.java b/src/net/mightypork/rcalc/ParseError.java
new file mode 100644
index 0000000..b35874c
--- /dev/null
+++ b/src/net/mightypork/rcalc/ParseError.java
@@ -0,0 +1,32 @@
+package net.mightypork.rcalc;
+
+
+/**
+ * Error thrown when a syntax error is encountered while parsing an expression
+ * 
+ * @author Ondrej Hruska
+ */
+public class ParseError extends RuntimeException {
+
+	/**
+	 * Create new parse error
+	 * 
+	 * @param message error message
+	 */
+	public ParseError(String message) {
+
+		super(message);
+	}
+
+
+	/**
+	 * Wrapper another exception in a parse error
+	 * 
+	 * @param e other exception
+	 */
+	public ParseError(Exception e) {
+
+		super(e);
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/RCalc.java b/src/net/mightypork/rcalc/RCalc.java
new file mode 100644
index 0000000..c160ca7
--- /dev/null
+++ b/src/net/mightypork/rcalc/RCalc.java
@@ -0,0 +1,74 @@
+package net.mightypork.rcalc;
+
+
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Rational calculator, expression parser returning fractional results instead
+ * of imprecise decimal values.
+ * 
+ * @author Ondrej Hruska
+ */
+public class RCalc implements IDebugable {
+
+	/** Debug mode flag */
+	private boolean debug = false;
+	/** Tokenizer instance */
+	private Tokenizer tokenizer = new Tokenizer();
+
+
+	/**
+	 * Create new rational calculator
+	 */
+	public RCalc() {
+
+	}
+
+
+	@Override
+	public boolean isDebug() {
+
+		return debug;
+	}
+
+
+	@Override
+	public void setDebug(boolean debug) {
+
+		tokenizer.setDebug(debug);
+		this.debug = debug;
+	}
+
+
+	/**
+	 * Calculate a result of an expression.
+	 * 
+	 * @param expression input expression
+	 * @return computed result
+	 */
+	public Fraction evaluate(String expression) {
+
+		IEvaluable ev;
+
+
+		try {
+			TokenList tl = tokenizer.tokenize(expression);
+
+			if (debug) System.out.println("\nBuilding syntax tree...");
+
+			ev = tl.parse();
+		} catch (ParseError e) {
+			throw e;
+		} catch (NumberFormatException e) {
+			throw new ParseError("Invalid number format.");
+		} catch (Exception e) {
+			throw new ParseError(e);
+		}
+
+		if (debug) System.out.println("\nSyntax tree:\n" + ev + "\n");
+
+		Fraction out = ev.evaluate();
+		return out;
+	}
+}
diff --git a/src/net/mightypork/rcalc/RCalcSession.java b/src/net/mightypork/rcalc/RCalcSession.java
new file mode 100644
index 0000000..92c779e
--- /dev/null
+++ b/src/net/mightypork/rcalc/RCalcSession.java
@@ -0,0 +1,172 @@
+package net.mightypork.rcalc;
+
+
+import java.util.HashMap;
+import java.util.Map.Entry;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Rational Calculator Session - interactive RCalc with possibility to set and
+ * use variables.
+ * 
+ * @author Ondrej Hruska
+ */
+public class RCalcSession implements IDebugable {
+
+	/** Debug mode flag */
+	private boolean debug = false;
+	/** Calculator instance */
+	private RCalc rcalc = new RCalc();
+	/** Table of user defined variables */
+	private HashMap<String, Fraction> symbolTable = new HashMap<String, Fraction>();
+
+
+	@Override
+	public boolean isDebug() {
+
+		return debug;
+	}
+
+
+	@Override
+	public void setDebug(boolean debug) {
+
+		rcalc.setDebug(debug);
+		this.debug = debug;
+	}
+
+
+	/**
+	 * Get variable value
+	 * 
+	 * @param name variable name
+	 * @return the value
+	 */
+	public Fraction getVariable(String name) {
+
+		return symbolTable.get(name.toLowerCase());
+	}
+
+
+	/**
+	 * Set a variable value
+	 * 
+	 * @param name variable name
+	 * @param value value to set
+	 */
+	public void setVariable(String name, Fraction value) {
+
+		symbolTable.put(name.trim(), value);
+	}
+
+
+	/**
+	 * Evaluate an expression
+	 * 
+	 * @param expression expression
+	 * @return result
+	 */
+	public Fraction evaluate(String expression) {
+
+		expression = expression.trim().toLowerCase();
+
+		if (expression.length() == 0) return null; // no operation
+
+		expression.replace(":=", "="); // normalize assignment sign
+
+		String assignedVariable = null;
+		String assignmentOperation = "";
+
+		// parse name=value syntax for variables
+		if (expression.matches("^[a-z]+\\s*[+\\-*/%^]?=\\s*(.+)$")) {
+			Pattern pattern = Pattern.compile("^([a-z]+)\\s*([+\\-*/%^]?=)\\s*(.+)$");
+			Matcher matcher = pattern.matcher(expression);
+
+			if (!matcher.find() || matcher.groupCount() != 3) {
+				throw new ParseError("Invalid expression format, check your syntax.");
+			}
+
+			assignedVariable = matcher.group(1).trim();
+			assignmentOperation = matcher.group(2).trim();
+			expression = matcher.group(3).trim();
+		}
+
+		// replace variable names with their values
+		for (Entry<String, Fraction> entry : symbolTable.entrySet()) {
+			String regex = "(?:(?<![a-z])|^)" + entry.getKey() + "(?:(?![a-z])|$)";
+			String replacement = "(" + entry.getValue() + ")";
+			expression = expression.replaceAll(regex, replacement);
+		}
+
+		// calculate result
+		Fraction result = rcalc.evaluate(expression);
+
+		// assign variable value if requested
+		if (assignedVariable != null) {
+
+			Fraction oldValue = symbolTable.get(assignedVariable);
+
+			if (oldValue == null) oldValue = Fraction.ZERO;
+
+			if (assignmentOperation.equals("=")) {
+				// no-op
+
+			} else if (assignmentOperation.equals("+=")) {
+
+				result = oldValue.add(result);
+
+			} else if (assignmentOperation.equals("-=")) {
+
+				result = oldValue.subtract(result);
+
+			} else if (assignmentOperation.equals("*=")) {
+
+				result = oldValue.multiply(result);
+
+			} else if (assignmentOperation.equals("/=")) {
+
+				result = oldValue.divide(result);
+
+			} else if (assignmentOperation.equals("%=")) {
+
+				result = oldValue.modulo(result);
+
+			} else if (assignmentOperation.equals("^=")) {
+
+				result = oldValue.power(result);
+			}
+
+			symbolTable.put(assignedVariable, result);
+		}
+
+		return result;
+	}
+
+
+	/**
+	 * Set symbol table (can be used to share it among multiple instances)
+	 * 
+	 * @param table the symbol table
+	 */
+	public void setSymbolTable(HashMap<String, Fraction> table) {
+
+		this.symbolTable = table;
+	}
+
+
+	/**
+	 * Get the current symbol table
+	 * 
+	 * @return symbol table
+	 */
+	public HashMap<String, Fraction> getSymbolTable() {
+
+		return symbolTable;
+	}
+
+
+}
diff --git a/src/net/mightypork/rcalc/TokenList.java b/src/net/mightypork/rcalc/TokenList.java
new file mode 100644
index 0000000..60fa0a7
--- /dev/null
+++ b/src/net/mightypork/rcalc/TokenList.java
@@ -0,0 +1,268 @@
+package net.mightypork.rcalc;
+
+
+import java.util.ArrayList;
+import java.util.Stack;
+
+import net.mightypork.rcalc.operations.Operation;
+import net.mightypork.rcalc.tokens.*;
+
+
+/**
+ * A list of tokens which can be parsed into a single IEvaluable
+ * 
+ * @author Ondrej Hruska
+ */
+public class TokenList extends ArrayList<IToken> implements IToken {
+
+	/**
+	 * Create a TokenList with defined initial size
+	 * 
+	 * @param i initial size
+	 */
+	public TokenList(int i) {
+
+		super(i);
+	}
+
+
+	/**
+	 * Create a blank TokenList
+	 */
+	public TokenList() {
+
+		super();
+	}
+
+
+	/**
+	 * Parse the token list.<br>
+	 * After running this method, the list is typically reduced to a single
+	 * token
+	 * 
+	 * @return the remaining token
+	 */
+	public IEvaluableToken parse() {
+
+		try {
+			// 1. Extract all parentheses into TokenLists
+			extractParentheses();
+
+			// 2. Convert operator tokens to operators, including their arguments
+			//    in the correct order ^ * / + -
+			extractOperator(TokenOperatorFactorial.class);
+			extractOperator(TokenOperatorPower.class);
+			extractOperator(TokenOperatorMultiply.class);
+			extractOperator(TokenOperatorDivide.class);
+			extractOperator(TokenOperatorModulo.class);
+			extractOperator(TokenOperatorAdd.class);
+			extractOperator(TokenOperatorSubtract.class);
+
+			// 3. Check for leftovers, throw error if any
+			if (this.size() > 1) {
+				throw new ParseError("TokenList didn't parse entirely, probably a syntax error: " + this);
+			}
+
+			// 4. If last token is a TokenList, use its content instead
+			if (this.get(0) instanceof TokenList) {
+				TokenList theList = (TokenList) this.get(0);
+				if (theList.size() == 1 && (theList.get(0) instanceof IEvaluableToken)) {
+					IEvaluableToken eval = (IEvaluableToken) theList.get(0);
+					this.clear();
+					this.add(eval);
+				}
+			}
+
+			// 5. Throw error if last token remaining is not evaluable
+			if (!(this.get(0) instanceof IEvaluableToken)) {
+				throw new ParseError("Last token in a TokenList is not evaluable: " + this.get(0));
+			}
+
+		} catch (ParseError e) {
+			throw e;
+		} catch (IndexOutOfBoundsException e) {
+			throw new ParseError("Missing operand(s).");
+		} catch (Exception e) {
+			throw new ParseError(e);
+		}
+
+		return (IEvaluableToken) this.get(0); // checked earlier
+	}
+
+
+	/**
+	 * Find tokens of given operator class, and convert them to the operations
+	 * including their operands.
+	 * 
+	 * @param operatorClass class of the operator to find
+	 */
+	private void extractOperator(Class<? extends IOperatorToken> operatorClass) {
+
+		Stack<Integer> positions = new Stack<Integer>();
+
+		// find operator positions
+		for (int i = size() - 1; i >= 0; i--) {
+			if (operatorClass.isInstance(get(i))) {
+				positions.push(i);
+			}
+		}
+
+		// offset, used when positions are updated while replacing tokens
+		int offset = 0;
+
+		while (!positions.isEmpty()) {
+
+			// get position of the next token
+			int pos = positions.pop() + offset;
+
+			IToken operatorToken = get(pos);
+
+			if (operatorToken instanceof TokenBinaryOperator) {
+
+				TokenBinaryOperator opToken = (TokenBinaryOperator) operatorToken;
+
+				// variables for tokenLists of the operands
+				TokenList leftTL, rightTL;
+
+				// get left operand
+				IToken leftArg = get(pos - 1);
+				if (leftArg instanceof TokenList) {
+					leftTL = (TokenList) leftArg;
+				} else {
+					leftTL = new TokenList(1);
+					leftTL.add(leftArg);
+				}
+
+				// get right operand
+				IToken rightArg = get(pos + 1);
+				if (rightArg instanceof TokenList) {
+					rightTL = (TokenList) rightArg;
+				} else {
+					rightTL = new TokenList(1);
+					rightTL.add(rightArg);
+				}
+
+				// build an operation
+				Operation op = opToken.toOperation(leftTL, rightTL);
+
+				// discard used tokens
+				subList(pos - 1, pos + 2).clear();
+				// put back the operation
+				add(pos - 1, op);
+				// shift offset
+				offset -= 2;
+
+			} else if (operatorToken instanceof TokenUnaryOperatorLeft) {
+
+				TokenUnaryOperatorLeft opToken = (TokenUnaryOperatorLeft) operatorToken;
+
+				// variable for left operand
+				TokenList leftTL;
+
+				// get left operand (the only one)
+				IToken leftArg = get(pos - 1);
+				if (leftArg instanceof TokenList) {
+					leftTL = (TokenList) leftArg;
+				} else {
+					leftTL = new TokenList(1);
+					leftTL.add(leftArg);
+				}
+
+				// build an operation
+				Operation op = opToken.toOperation(leftTL);
+
+				// discard used tokens
+				subList(pos - 1, pos + 1).clear();
+				// put back the operation
+				add(pos - 1, op);
+				// shift offset
+				offset -= 1;
+
+			} else if (operatorToken instanceof TokenUnaryOperatorRight) {
+
+				TokenUnaryOperatorRight opToken = (TokenUnaryOperatorRight) operatorToken;
+
+				// variable for left operand
+				TokenList rightTL;
+
+				// get right operand (the only one)
+				IToken rightArg = get(pos + 1);
+				if (rightArg instanceof TokenList) {
+					rightTL = (TokenList) rightArg;
+				} else {
+					rightTL = new TokenList(1);
+					rightTL.add(rightArg);
+				}
+
+				// build an operation
+				Operation op = opToken.toOperation(rightTL);
+
+				// discard used tokens
+				subList(pos, pos + 2).clear();
+				// put back the operation
+				add(pos, op);
+				// shift offset
+				offset -= 1;
+			}
+		}
+	}
+
+
+	/**
+	 * Convert outer parenthesized blocks to individual tokens
+	 */
+	private void extractParentheses() {
+
+		int open = 0; // level of outer parentheses
+		int openIgnored = 0; // level of inner parentheses, to be skipped
+
+		Stack<Integer> lefts = new Stack<Integer>();
+		Stack<Integer> rights = new Stack<Integer>();
+
+		for (int i = 0; i < size(); i++) {
+
+			if (get(i) instanceof TokenParenthesisLeft) {
+
+				if (open == 0) {
+					open++;
+					lefts.push(i);
+				} else {
+					openIgnored++;
+				}
+			}
+
+			if (get(i) instanceof TokenParenthesisRight) {
+
+				if (openIgnored > 0) {
+					openIgnored--;
+				} else {
+					open--;
+					if (open == 0) rights.push(i);
+				}
+			}
+		}
+
+		if (open > 0) throw new ParseError("Unbalanced parentheses.");
+
+		// extract token lists inside the outer parentheses, put them back as single tokens
+		while (!lefts.isEmpty()) {
+			int left = lefts.pop();
+			int right = rights.pop();
+
+			int innerLeft = left + 1;
+			int innerRight = right - 1;
+
+			// prepare tokenList for the inner tokens
+			TokenList insides = new TokenList();
+			// add the inner tokens
+			insides.addAll(subList(innerLeft, innerRight + 1));
+			// destroy the whole range including parentheses
+			subList(left, right + 1).clear();
+			// put replacement token back
+			add(left, insides.parse());
+		}
+
+	}
+
+
+}
diff --git a/src/net/mightypork/rcalc/Tokenizer.java b/src/net/mightypork/rcalc/Tokenizer.java
new file mode 100644
index 0000000..bc1d69d
--- /dev/null
+++ b/src/net/mightypork/rcalc/Tokenizer.java
@@ -0,0 +1,185 @@
+package net.mightypork.rcalc;
+
+
+import java.math.BigInteger;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import net.mightypork.rcalc.numbers.Fraction;
+import net.mightypork.rcalc.tokens.*;
+
+
+/**
+ * Utility for converting an expression from String to a list of tokens
+ * 
+ * @author Ondrej Hruska
+ */
+public class Tokenizer implements IDebugable {
+
+	/** Debug mode flag */
+	private boolean debug = false;
+
+	/** Deep debug mode flag */
+	private boolean deepDebug = false;
+
+
+	@Override
+	public boolean isDebug() {
+
+		return debug;
+	}
+
+
+	@Override
+	public void setDebug(boolean debug) {
+
+		this.debug = debug;
+	}
+
+
+	/**
+	 * Get if deep debug mode is enabled
+	 * 
+	 * @return is in deep debug mode
+	 */
+	public boolean isDeepDebug() {
+
+		return deepDebug && debug;
+	}
+
+
+	/**
+	 * Enable / disable deep debug mode
+	 * 
+	 * @param debug
+	 */
+	public void setDeepDebug(boolean debug) {
+
+		this.deepDebug = this.debug = debug;
+	}
+
+
+	/**
+	 * Parse a string to a list of expression tokens
+	 * 
+	 * @param input string with expression to parse
+	 * @return token list
+	 */
+	public TokenList tokenize(String input) {
+
+		// discard whitespace
+		input = input.replaceAll("\\s", "");
+
+		// check parentheses
+		int level = 0;
+		for (char c : input.toCharArray()) {
+			if (c == '(') level++;
+			if (c == ')') level--;
+
+			if (level < 0) throw new ParseError("Unbalanced parentheses.");
+		}
+		if (level != 0) throw new ParseError("Unbalanced parentheses.");
+
+		// translate ** to ^
+		input = input.replaceAll("[*]{2}", "^");
+		if (debug && deepDebug) System.out.println("\nTranslate '**' to '^'\n" + input);
+
+		// enclose ^ left operand in parentheses
+		input = input.replaceAll("([0-9.]+[!]?)\\^", "($1)^");
+		if (debug && deepDebug) System.out.println("\nWrap left numeric operand of '^' with parentheses\n" + input);
+
+		// add multiplication operator for implicit multiplication
+		input = input.replaceAll("(?<=[0-9)!])(?=[(])", "*"); // )( -> )*(
+		input = input.replaceAll("(?<=[)!])(?=[0-9(])", "*");
+		if (debug && deepDebug) System.out.println("\nApply implicit multiplication\n" + input);
+
+		// normalize series of '+' and '-'
+		StringBuffer outputBuffer = new StringBuffer();
+		Matcher matcher = Pattern.compile("([+\\-]{2,})").matcher(input);
+		while (matcher.find()) {
+			int minus = 0;
+			for (char c : matcher.group().toCharArray()) {
+				if (c == '-') minus++;
+			}
+			minus = minus % 2;
+			matcher.appendReplacement(outputBuffer, minus == 0 ? "+" : "-");
+		}
+		matcher.appendTail(outputBuffer);
+		input = outputBuffer.toString();
+		if (debug && deepDebug) System.out.println("\nNormalize sequences of '+' and '-'\n" + input);
+
+		// turn '-' to '+-' between numbers
+		input = input.replaceAll("(?<=[0-9)!])-(?=[0-9])", "+-");
+		if (debug && deepDebug) System.out.println("\n'-' to '+-' between numbers\n" + input);
+
+		// convert '-' to '+-1*' in front of non-numbers
+		input = input.replaceAll("-(?=[^0-9])", "+-1*");
+		if (debug && deepDebug) System.out.println("\n'-' to '+-1*' in front of non-numbers\n" + input);
+
+		// discard useless + signs
+		input = input.replaceAll("(?<=[^)0-9!]|^)\\+", "");
+		if (debug && deepDebug) System.out.println("\nDiscard '+' at beginning of scope\n" + input);
+
+		if (debug) System.out.println("\nParsing tokens...");
+
+		TokenList list = new TokenList();
+
+		String buffer = "";
+
+		boolean parsingNumber = false;
+
+		for (Character c : input.toCharArray()) {
+			if (c.toString().matches("[\\-0-9.]")) {
+				buffer += c;
+				parsingNumber = true;
+			} else {
+
+				if (parsingNumber) {
+					list.add(new Fraction(buffer));
+					buffer = "";
+					parsingNumber = false;
+				}
+
+				switch (c) {
+					case '(':
+						list.add(new TokenParenthesisLeft());
+						break;
+					case ')':
+						list.add(new TokenParenthesisRight());
+						break;
+					case '*':
+						list.add(new TokenOperatorMultiply());
+						break;
+					case '/':
+						list.add(new TokenOperatorDivide());
+						break;
+					case '+':
+						list.add(new TokenOperatorAdd());
+						break;
+					case '!':
+						list.add(new TokenOperatorFactorial());
+						break;
+					case '%':
+						list.add(new TokenOperatorModulo());
+						break;
+					case '^':
+						list.add(new TokenOperatorPower());
+						break;
+					default:
+						throw new ParseError("Unknown token " + c);
+				}
+
+			}
+		}
+
+		// include possible last number
+		if (parsingNumber) {
+			list.add(new Fraction(buffer));
+		}
+
+		if (debug) System.out.println("\nToken list:\n" + list);
+
+
+		return list;
+	}
+}
diff --git a/src/net/mightypork/rcalc/numbers/Fraction.java b/src/net/mightypork/rcalc/numbers/Fraction.java
new file mode 100644
index 0000000..9c53326
--- /dev/null
+++ b/src/net/mightypork/rcalc/numbers/Fraction.java
@@ -0,0 +1,451 @@
+package net.mightypork.rcalc.numbers;
+
+
+import java.math.BigInteger;
+
+import net.mightypork.rcalc.IEvaluableToken;
+import net.mightypork.rcalc.ParseError;
+
+
+/**
+ * A fractional number with methods for basic arithmetics
+ * 
+ * @author Ondrej Hruska
+ */
+public class Fraction implements IEvaluableToken {
+
+	/** Zero fraction (0/1) */
+	public static final Fraction ZERO = new Fraction(BigInteger.ZERO);
+	/** One fraction (1/1) */
+	public static final Fraction ONE = new Fraction(BigInteger.ZERO);
+
+
+	private BigInteger numerator = BigInteger.ZERO;
+	private BigInteger denominator = BigInteger.ONE;
+
+
+	/**
+	 * Create fraction from numerator and 1 as denominator
+	 * 
+	 * @param numerator numerator
+	 */
+	public Fraction(long numerator) {
+
+		this.numerator = BigInteger.valueOf(numerator);
+		this.denominator = BigInteger.ONE;
+	}
+
+
+	/**
+	 * Create fraction from numerator and 1 as denominator
+	 * 
+	 * @param numerator numerator
+	 */
+	public Fraction(BigInteger numerator) {
+
+		this.numerator = numerator;
+		this.denominator = BigInteger.ONE;
+	}
+
+
+	/**
+	 * Create fraction from numerator and denominator
+	 * 
+	 * @param numerator numerator
+	 * @param denominator denominator
+	 */
+	public Fraction(long numerator, long denominator) {
+
+		if (denominator == 0) {
+			throw new ArithmeticException("Division by zero.");
+		}
+
+		this.numerator = BigInteger.valueOf(numerator);
+		this.denominator = BigInteger.valueOf(denominator);
+	}
+
+
+	/**
+	 * Create fraction from numerator and denominator
+	 * 
+	 * @param numerator numerator
+	 * @param denominator denominator
+	 */
+	public Fraction(BigInteger numerator, BigInteger denominator) {
+
+		if (denominator.equals(BigInteger.ZERO)) {
+			throw new ArithmeticException("Division by zero.");
+		}
+
+		this.numerator = numerator;
+		this.denominator = denominator;
+	}
+
+
+	/**
+	 * Create a fraction as a copy of another
+	 * 
+	 * @param other other fraction to copy
+	 */
+	public Fraction(Fraction other) {
+
+		this.numerator = other.numerator;
+		this.denominator = other.denominator;
+	}
+
+
+	public Fraction(String number) {
+		if(number.contains(".")) {
+			String[] parts = number.split("[.]");
+			try{
+				if(parts.length != 2) throw new ParseError(""); // for the catch
+				this.numerator = new BigInteger(parts[0]+parts[1]);
+				this.denominator = BigInteger.valueOf(10).pow(parts[1].length());
+				this.simplify_ip();
+			}catch(Exception e) {
+				e.printStackTrace();
+				throw new ParseError("Invalid number format.");
+			}
+		} else {
+			this.numerator = new BigInteger(number);
+			this.denominator = BigInteger.ONE;
+		}
+	}
+
+
+	/**
+	 * Get numerator number
+	 * 
+	 * @return numerator
+	 */
+	public BigInteger getNumerator() {
+
+		return numerator;
+	}
+
+
+	/**
+	 * Get denominator number
+	 * 
+	 * @return numerator
+	 */
+	public BigInteger getDenominator() {
+
+		return numerator;
+	}
+
+
+	/**
+	 * Add a number
+	 * 
+	 * @param operand addend
+	 * @return this + addend
+	 */
+	public Fraction add(Fraction operand) {
+
+		Fraction a = this.getCopy();
+		Fraction b = operand.getCopy();
+
+		a.numerator = a.numerator.multiply(b.denominator);
+		b.numerator = b.numerator.multiply(a.denominator);
+		a.denominator = a.denominator.multiply(b.denominator);
+
+		a.numerator = a.numerator.add(b.numerator);
+
+		return a.simplify();
+	}
+
+
+	/**
+	 * Subtract a number
+	 * 
+	 * @param operand subtrahend
+	 * @return this - subtrahend
+	 */
+	public Fraction subtract(Fraction operand) {
+
+		Fraction negated = new Fraction(operand.numerator.negate(), operand.denominator);
+		return this.add(negated);
+	}
+
+
+	/**
+	 * Multiply by a number
+	 * 
+	 * @param operand multiplier
+	 * @return this * multiplier
+	 */
+	public Fraction multiply(Fraction operand) {
+
+		BigInteger n = numerator.multiply(operand.numerator);
+		BigInteger d = denominator.multiply(operand.denominator);
+		return (new Fraction(n, d)).simplify();
+	}
+
+
+	/**
+	 * Divide by a number
+	 * 
+	 * @param operand divisor
+	 * @return this / divisor
+	 */
+	public Fraction divide(Fraction operand) {
+
+		Fraction flipped = new Fraction(operand.denominator, operand.numerator);
+		return this.multiply(flipped);
+	}
+
+
+	/**
+	 * Modulo with a number
+	 * 
+	 * @param operand divisor
+	 * @return this % divisor
+	 */
+	public Fraction modulo(Fraction operand) {
+
+		if (isFractional() || operand.isFractional()) {
+			throw new ArithmeticException("Modulo is not defined for fractional operands.");
+		}
+
+		BigInteger i = this.getBigIntegerValue();
+		BigInteger o = operand.getBigIntegerValue();
+
+		return new Fraction(i.mod(o));
+	}
+
+
+	/**
+	 * Get an n-th power of the number
+	 * 
+	 * @param operand power
+	 * @return this ^ power
+	 */
+	public Fraction power(Fraction operand) {
+
+		if (operand.isFractional()) {
+			throw new ArithmeticException("Can't calculate fractional power.");
+		}
+
+		int power = operand.getIntegerValue();
+
+		boolean swap = power < 0;
+
+		power = Math.abs(power);
+
+		BigInteger n = numerator.pow(power);
+		BigInteger d = denominator.pow(power);
+
+		Fraction out = (new Fraction(n, d)).simplify();
+
+		if (swap) out = out.invert();
+
+		return out;
+	}
+
+
+	/**
+	 * Get a fraction with swapped numerator and denominator.
+	 * 
+	 * @return inverted fraction
+	 */
+	public Fraction invert() {
+
+		if (numerator.equals(BigInteger.ZERO)) {
+			throw new ArithmeticException("Division by zero.");
+		}
+
+		return new Fraction(denominator, numerator);
+	}
+
+
+	/**
+	 * Simplify the fraction
+	 * 
+	 * @return simplified fraction
+	 */
+	public Fraction simplify() {
+
+		BigInteger gcd = numerator.gcd(denominator);
+
+		return new Fraction(numerator.divide(gcd), denominator.divide(gcd));
+	}
+	
+
+
+	/**
+	 * Simplify the fraction (in place)
+	 */
+	private void simplify_ip() {
+		BigInteger gcd = numerator.gcd(denominator);
+
+		numerator = numerator.divide(gcd);
+		denominator = denominator.divide(gcd);
+	}
+
+
+	/**
+	 * Check if the number is fractional
+	 * 
+	 * @return is fractional
+	 */
+	public boolean isFractional() {
+
+		return !(numerator.mod(denominator)).equals(BigInteger.ZERO);
+	}
+
+
+	/**
+	 * Get an integer numeric value
+	 * 
+	 * @return value
+	 * @throws UnsupportedOperationException for fractional numbers
+	 */
+	public int getIntegerValue() {
+
+		if (isFractional()) {
+			throw new ArithmeticException("Can't take integer value of a fractional number.");
+		}
+
+		BigInteger a = numerator.divide(denominator);
+		if (a.longValue() > Integer.MAX_VALUE) {
+			throw new ArithmeticException("Can't convert to integer, number is too big.");
+		}
+
+		return a.intValue();
+	}
+
+
+	/**
+	 * Get a BigInteger numeric value
+	 * 
+	 * @return value
+	 * @throws UnsupportedOperationException for fractional numbers
+	 */
+	public BigInteger getBigIntegerValue() {
+
+		if (this.isFractional()) {
+			throw new ArithmeticException("Can't take BigInteger value of a fractional number.");
+		}
+
+		return numerator.divide(denominator);
+	}
+
+
+	/**
+	 * Get a double-precision numeric value
+	 * 
+	 * @return value
+	 */
+	public double getDoubleValue() {
+
+		double a = numerator.doubleValue();
+		double b = denominator.doubleValue();
+
+		if (Double.isInfinite(a) || Double.isInfinite(b)) {
+			throw new ArithmeticException("Can't convert BigInteger to double, number is too big.");
+		}
+
+		return a / b;
+	}
+
+
+	/**
+	 * Get a identical copy of this fraction
+	 * 
+	 * @return copy
+	 */
+	private Fraction getCopy() {
+
+		return new Fraction(this);
+	}
+
+
+	@Override
+	public int hashCode() {
+
+		final int prime = 31;
+		int result = 1;
+		result = prime * result + ((denominator == null) ? 0 : denominator.hashCode());
+		result = prime * result + ((numerator == null) ? 0 : numerator.hashCode());
+		return result;
+	}
+
+
+	@Override
+	public boolean equals(Object obj) {
+
+		if (this == obj) return true;
+		if (obj == null) return false;
+		if (getClass() != obj.getClass()) return false;
+		Fraction other = (Fraction) obj;
+
+		if (denominator == null || other.denominator == null) return false;
+		if (numerator == null || other.numerator == null) return false;
+
+		Fraction thisSimplified = this.simplify();
+		Fraction otherSimplified = other.simplify();
+
+		return thisSimplified.numerator.equals(otherSimplified.numerator) && thisSimplified.denominator.equals(otherSimplified.denominator);
+	}
+
+
+	/**
+	 * Check if the toString() of this fraction equals to the given string
+	 * 
+	 * @param str compared string
+	 * @return equals
+	 */
+	public boolean equalsToString(String str) {
+
+		return this.toString().equals(str);
+	}
+
+
+	/**
+	 * Get a string representation of this fraction in the format
+	 * "numerator/denominator", alternatively "numerator" if denominator is
+	 * equal to 1.
+	 */
+	@Override
+	public String toString() {
+
+		if (!isFractional()) return numerator.divide(denominator).toString();
+
+		return numerator + "/" + denominator;
+	}
+
+
+	@Override
+	public Fraction evaluate() {
+
+		return this;
+	}
+
+
+	/**
+	 * Take a factorial of this number, provided it is not fractional.
+	 * 
+	 * @return the factorial
+	 */
+	public Fraction factorial() {
+
+		if (this.isFractional()) {
+			throw new ArithmeticException("Can't get factorial of a fractional number.");
+		}
+
+		BigInteger val = getBigIntegerValue();
+
+		if (val.compareTo(BigInteger.ZERO) < 0) {
+			throw new ArithmeticException("Can't get factorial of a negative number.");
+		}
+
+		BigInteger result = BigInteger.ONE;
+		for (BigInteger cnt = BigInteger.ONE; cnt.compareTo(val) <= 0; cnt = cnt.add(BigInteger.ONE)) {
+			result = result.multiply(cnt);
+		}
+
+		return new Fraction(result, BigInteger.ONE);
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/operations/BinaryOperation.java b/src/net/mightypork/rcalc/operations/BinaryOperation.java
new file mode 100644
index 0000000..d46beaa
--- /dev/null
+++ b/src/net/mightypork/rcalc/operations/BinaryOperation.java
@@ -0,0 +1,37 @@
+package net.mightypork.rcalc.operations;
+
+
+import net.mightypork.rcalc.IEvaluable;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Abstract operation with two operands
+ * 
+ * @author Ondrej Hruska
+ */
+public abstract class BinaryOperation extends Operation {
+
+	/** Left operand */
+	protected IEvaluable left = null;
+	/** Right operand */
+	protected IEvaluable right = null;
+
+
+	/**
+	 * Create a binary operation
+	 * 
+	 * @param left left operand
+	 * @param right right operand
+	 */
+	public BinaryOperation(IEvaluable left, IEvaluable right) {
+
+		this.left = left;
+		this.right = right;
+	}
+
+
+	@Override
+	public abstract Fraction evaluate();
+
+}
diff --git a/src/net/mightypork/rcalc/operations/Operation.java b/src/net/mightypork/rcalc/operations/Operation.java
new file mode 100644
index 0000000..cd3254d
--- /dev/null
+++ b/src/net/mightypork/rcalc/operations/Operation.java
@@ -0,0 +1,17 @@
+package net.mightypork.rcalc.operations;
+
+
+import net.mightypork.rcalc.IEvaluableToken;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Abstract operation
+ * 
+ * @author Ondrej Hruska
+ */
+public abstract class Operation implements IEvaluableToken {
+
+	@Override
+	public abstract Fraction evaluate();
+}
diff --git a/src/net/mightypork/rcalc/operations/OperationAdd.java b/src/net/mightypork/rcalc/operations/OperationAdd.java
new file mode 100644
index 0000000..ee5d5bb
--- /dev/null
+++ b/src/net/mightypork/rcalc/operations/OperationAdd.java
@@ -0,0 +1,39 @@
+package net.mightypork.rcalc.operations;
+
+
+import net.mightypork.rcalc.IEvaluable;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Addition
+ * 
+ * @author Ondrej Hruska
+ */
+public class OperationAdd extends BinaryOperation {
+
+	/**
+	 * Create addition
+	 * 
+	 * @param left left operand
+	 * @param right right operand
+	 */
+	public OperationAdd(IEvaluable left, IEvaluable right) {
+
+		super(left, right);
+	}
+
+
+	@Override
+	public Fraction evaluate() {
+
+		return left.evaluate().add(right.evaluate());
+	}
+
+
+	@Override
+	public String toString() {
+
+		return "ADD{" + left + "," + right + "}";
+	}
+}
diff --git a/src/net/mightypork/rcalc/operations/OperationDivide.java b/src/net/mightypork/rcalc/operations/OperationDivide.java
new file mode 100644
index 0000000..886ffe0
--- /dev/null
+++ b/src/net/mightypork/rcalc/operations/OperationDivide.java
@@ -0,0 +1,40 @@
+package net.mightypork.rcalc.operations;
+
+
+import net.mightypork.rcalc.IEvaluable;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Division
+ * 
+ * @author Ondrej Hruska
+ */
+public class OperationDivide extends BinaryOperation {
+
+	/**
+	 * Create division
+	 * 
+	 * @param left left operand
+	 * @param right right operand
+	 */
+	public OperationDivide(IEvaluable left, IEvaluable right) {
+
+		super(left, right);
+	}
+
+
+	@Override
+	public Fraction evaluate() {
+
+		return left.evaluate().divide(right.evaluate());
+	}
+
+
+	@Override
+	public String toString() {
+
+		return "DIV{" + left + "," + right + "}";
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/operations/OperationFactorial.java b/src/net/mightypork/rcalc/operations/OperationFactorial.java
new file mode 100644
index 0000000..d5d56a9
--- /dev/null
+++ b/src/net/mightypork/rcalc/operations/OperationFactorial.java
@@ -0,0 +1,38 @@
+package net.mightypork.rcalc.operations;
+
+
+import net.mightypork.rcalc.IEvaluable;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Factorial
+ * 
+ * @author Ondrej Hruska
+ */
+public class OperationFactorial extends UnaryOperation {
+
+	/**
+	 * Create factorial
+	 * 
+	 * @param operand operand
+	 */
+	public OperationFactorial(IEvaluable operand) {
+
+		super(operand);
+	}
+
+
+	@Override
+	public Fraction evaluate() {
+
+		return operand.evaluate().factorial();
+	}
+
+
+	@Override
+	public String toString() {
+
+		return "FCT{" + operand + "}";
+	}
+}
diff --git a/src/net/mightypork/rcalc/operations/OperationModulo.java b/src/net/mightypork/rcalc/operations/OperationModulo.java
new file mode 100644
index 0000000..fc118e9
--- /dev/null
+++ b/src/net/mightypork/rcalc/operations/OperationModulo.java
@@ -0,0 +1,39 @@
+package net.mightypork.rcalc.operations;
+
+
+import net.mightypork.rcalc.IEvaluable;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Modulo
+ * 
+ * @author Ondrej Hruska
+ */
+public class OperationModulo extends BinaryOperation {
+
+	/**
+	 * Create modulo
+	 * 
+	 * @param left left operand
+	 * @param right right operand
+	 */
+	public OperationModulo(IEvaluable left, IEvaluable right) {
+
+		super(left, right);
+	}
+
+
+	@Override
+	public Fraction evaluate() {
+
+		return left.evaluate().modulo(right.evaluate());
+	}
+
+
+	@Override
+	public String toString() {
+
+		return "MOD{" + left + "," + right + "}";
+	}
+}
diff --git a/src/net/mightypork/rcalc/operations/OperationMultiply.java b/src/net/mightypork/rcalc/operations/OperationMultiply.java
new file mode 100644
index 0000000..791fc54
--- /dev/null
+++ b/src/net/mightypork/rcalc/operations/OperationMultiply.java
@@ -0,0 +1,40 @@
+package net.mightypork.rcalc.operations;
+
+
+import net.mightypork.rcalc.IEvaluable;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Multiplication
+ * 
+ * @author Ondrej Hruska
+ */
+public class OperationMultiply extends BinaryOperation {
+
+	/**
+	 * Create multiplication
+	 * 
+	 * @param left left operand
+	 * @param right right operand
+	 */
+	public OperationMultiply(IEvaluable left, IEvaluable right) {
+
+		super(left, right);
+	}
+
+
+	@Override
+	public Fraction evaluate() {
+
+		return left.evaluate().multiply(right.evaluate());
+	}
+
+
+	@Override
+	public String toString() {
+
+		return "MUL{" + left + "," + right + "}";
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/operations/OperationPower.java b/src/net/mightypork/rcalc/operations/OperationPower.java
new file mode 100644
index 0000000..8fe3bcf
--- /dev/null
+++ b/src/net/mightypork/rcalc/operations/OperationPower.java
@@ -0,0 +1,40 @@
+package net.mightypork.rcalc.operations;
+
+
+import net.mightypork.rcalc.IEvaluable;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Exponentiation
+ * 
+ * @author Ondrej Hruska
+ */
+public class OperationPower extends BinaryOperation {
+
+	/**
+	 * Create exponentiation
+	 * 
+	 * @param left left operand
+	 * @param right right operand
+	 */
+	public OperationPower(IEvaluable left, IEvaluable right) {
+
+		super(left, right);
+	}
+
+
+	@Override
+	public Fraction evaluate() {
+
+		return left.evaluate().power(right.evaluate());
+	}
+
+
+	@Override
+	public String toString() {
+
+		return "POW{" + left + "," + right + "}";
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/operations/OperationSubtract.java b/src/net/mightypork/rcalc/operations/OperationSubtract.java
new file mode 100644
index 0000000..307cc0d
--- /dev/null
+++ b/src/net/mightypork/rcalc/operations/OperationSubtract.java
@@ -0,0 +1,40 @@
+package net.mightypork.rcalc.operations;
+
+
+import net.mightypork.rcalc.IEvaluable;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Subtraction
+ * 
+ * @author Ondrej Hruska
+ */
+public class OperationSubtract extends BinaryOperation {
+
+	/**
+	 * Create subtraction
+	 * 
+	 * @param left left operand
+	 * @param right right operand
+	 */
+	public OperationSubtract(IEvaluable left, IEvaluable right) {
+
+		super(left, right);
+	}
+
+
+	@Override
+	public Fraction evaluate() {
+
+		return left.evaluate().subtract(right.evaluate());
+	}
+
+
+	@Override
+	public String toString() {
+
+		return "SUB{" + left + "," + right + "}";
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/operations/UnaryOperation.java b/src/net/mightypork/rcalc/operations/UnaryOperation.java
new file mode 100644
index 0000000..c131787
--- /dev/null
+++ b/src/net/mightypork/rcalc/operations/UnaryOperation.java
@@ -0,0 +1,33 @@
+package net.mightypork.rcalc.operations;
+
+
+import net.mightypork.rcalc.IEvaluable;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Abstract unary operator
+ * 
+ * @author Ondrej Hruska
+ */
+public abstract class UnaryOperation extends Operation {
+
+	/** Operand */
+	protected IEvaluable operand = null;
+
+
+	/**
+	 * Create unary operation
+	 * 
+	 * @param operand operand
+	 */
+	public UnaryOperation(IEvaluable operand) {
+
+		this.operand = operand;
+	}
+
+
+	@Override
+	public abstract Fraction evaluate();
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/IOperatorToken.java b/src/net/mightypork/rcalc/tokens/IOperatorToken.java
new file mode 100644
index 0000000..a330571
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/IOperatorToken.java
@@ -0,0 +1,14 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.IToken;
+
+
+/**
+ * Interface of an operator token
+ * 
+ * @author Ondrej Hruska
+ */
+public interface IOperatorToken extends IToken {
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenBinaryOperator.java b/src/net/mightypork/rcalc/tokens/TokenBinaryOperator.java
new file mode 100644
index 0000000..7709e2c
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenBinaryOperator.java
@@ -0,0 +1,23 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.TokenList;
+import net.mightypork.rcalc.operations.Operation;
+
+
+/**
+ * Abstract operation token with two operands
+ * 
+ * @author Ondrej Hruska
+ */
+public abstract class TokenBinaryOperator implements IOperatorToken {
+
+	/**
+	 * Convert to operation
+	 * 
+	 * @param left left operand
+	 * @param right right operand
+	 * @return operation
+	 */
+	public abstract Operation toOperation(TokenList left, TokenList right);
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenOperatorAdd.java b/src/net/mightypork/rcalc/tokens/TokenOperatorAdd.java
new file mode 100644
index 0000000..ec020ca
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenOperatorAdd.java
@@ -0,0 +1,29 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.TokenList;
+import net.mightypork.rcalc.operations.Operation;
+import net.mightypork.rcalc.operations.OperationAdd;
+
+
+/**
+ * Addition token
+ * 
+ * @author Ondrej Hruska
+ */
+public class TokenOperatorAdd extends TokenBinaryOperator {
+
+	@Override
+	public String toString() {
+
+		return "+";
+	}
+
+
+	@Override
+	public Operation toOperation(TokenList left, TokenList right) {
+
+		return new OperationAdd(left.parse(), right.parse());
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenOperatorDivide.java b/src/net/mightypork/rcalc/tokens/TokenOperatorDivide.java
new file mode 100644
index 0000000..536a4e4
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenOperatorDivide.java
@@ -0,0 +1,29 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.TokenList;
+import net.mightypork.rcalc.operations.Operation;
+import net.mightypork.rcalc.operations.OperationDivide;
+
+
+/**
+ * Division token
+ * 
+ * @author Ondrej Hruska
+ */
+public class TokenOperatorDivide extends TokenBinaryOperator {
+
+	@Override
+	public String toString() {
+
+		return "/";
+	}
+
+
+	@Override
+	public Operation toOperation(TokenList left, TokenList right) {
+
+		return new OperationDivide(left.parse(), right.parse());
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenOperatorFactorial.java b/src/net/mightypork/rcalc/tokens/TokenOperatorFactorial.java
new file mode 100644
index 0000000..e8ac8f3
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenOperatorFactorial.java
@@ -0,0 +1,29 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.TokenList;
+import net.mightypork.rcalc.operations.Operation;
+import net.mightypork.rcalc.operations.OperationFactorial;
+
+
+/**
+ * Factorial token
+ * 
+ * @author Ondrej Hruska
+ */
+public class TokenOperatorFactorial extends TokenUnaryOperatorLeft {
+
+	@Override
+	public String toString() {
+
+		return "!";
+	}
+
+
+	@Override
+	public Operation toOperation(TokenList argument) {
+
+		return new OperationFactorial(argument.parse());
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenOperatorModulo.java b/src/net/mightypork/rcalc/tokens/TokenOperatorModulo.java
new file mode 100644
index 0000000..2e0237c
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenOperatorModulo.java
@@ -0,0 +1,29 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.TokenList;
+import net.mightypork.rcalc.operations.Operation;
+import net.mightypork.rcalc.operations.OperationModulo;
+
+
+/**
+ * Modulo token
+ * 
+ * @author Ondrej Hruska
+ */
+public class TokenOperatorModulo extends TokenBinaryOperator {
+
+	@Override
+	public String toString() {
+
+		return "%";
+	}
+
+
+	@Override
+	public Operation toOperation(TokenList left, TokenList right) {
+
+		return new OperationModulo(left.parse(), right.parse());
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenOperatorMultiply.java b/src/net/mightypork/rcalc/tokens/TokenOperatorMultiply.java
new file mode 100644
index 0000000..cae8f32
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenOperatorMultiply.java
@@ -0,0 +1,29 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.TokenList;
+import net.mightypork.rcalc.operations.Operation;
+import net.mightypork.rcalc.operations.OperationMultiply;
+
+
+/**
+ * Multiplication token
+ * 
+ * @author Ondrej Hruska
+ */
+public class TokenOperatorMultiply extends TokenBinaryOperator {
+
+	@Override
+	public String toString() {
+
+		return "*";
+	}
+
+
+	@Override
+	public Operation toOperation(TokenList left, TokenList right) {
+
+		return new OperationMultiply(left.parse(), right.parse());
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenOperatorPower.java b/src/net/mightypork/rcalc/tokens/TokenOperatorPower.java
new file mode 100644
index 0000000..49085f1
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenOperatorPower.java
@@ -0,0 +1,29 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.TokenList;
+import net.mightypork.rcalc.operations.Operation;
+import net.mightypork.rcalc.operations.OperationPower;
+
+
+/**
+ * Exponentiation token
+ * 
+ * @author Ondrej Hruska
+ */
+public class TokenOperatorPower extends TokenBinaryOperator {
+
+	@Override
+	public String toString() {
+
+		return "^";
+	}
+
+
+	@Override
+	public Operation toOperation(TokenList left, TokenList right) {
+
+		return new OperationPower(left.parse(), right.parse());
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenOperatorSubtract.java b/src/net/mightypork/rcalc/tokens/TokenOperatorSubtract.java
new file mode 100644
index 0000000..22db6bc
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenOperatorSubtract.java
@@ -0,0 +1,29 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.TokenList;
+import net.mightypork.rcalc.operations.Operation;
+import net.mightypork.rcalc.operations.OperationSubtract;
+
+
+/**
+ * Subtraction token
+ * 
+ * @author Ondrej Hruska
+ */
+public class TokenOperatorSubtract extends TokenBinaryOperator {
+
+	@Override
+	public String toString() {
+
+		return "-";
+	}
+
+
+	@Override
+	public Operation toOperation(TokenList left, TokenList right) {
+
+		return new OperationSubtract(left.parse(), right.parse());
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenParenthesisLeft.java b/src/net/mightypork/rcalc/tokens/TokenParenthesisLeft.java
new file mode 100644
index 0000000..9e78600
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenParenthesisLeft.java
@@ -0,0 +1,20 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.IToken;
+
+
+/**
+ * Left parenthesis token
+ * 
+ * @author Ondrej Hruska
+ */
+public class TokenParenthesisLeft implements IToken {
+
+	@Override
+	public String toString() {
+
+		return "(";
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenParenthesisRight.java b/src/net/mightypork/rcalc/tokens/TokenParenthesisRight.java
new file mode 100644
index 0000000..73eca62
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenParenthesisRight.java
@@ -0,0 +1,20 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.IToken;
+
+
+/**
+ * Right parenthesis token
+ * 
+ * @author Ondrej Hruska
+ */
+public class TokenParenthesisRight implements IToken {
+
+	@Override
+	public String toString() {
+
+		return ")";
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorLeft.java b/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorLeft.java
new file mode 100644
index 0000000..e74d07e
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorLeft.java
@@ -0,0 +1,22 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.TokenList;
+import net.mightypork.rcalc.operations.Operation;
+
+
+/**
+ * Abstract operator token with one operand on left
+ * 
+ * @author Ondrej Hruska
+ */
+public abstract class TokenUnaryOperatorLeft implements IOperatorToken {
+
+	/**
+	 * Convert to operation
+	 * 
+	 * @param operand operand
+	 * @return operation
+	 */
+	public abstract Operation toOperation(TokenList operand);
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorRight.java b/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorRight.java
new file mode 100644
index 0000000..2812ced
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorRight.java
@@ -0,0 +1,22 @@
+package net.mightypork.rcalc.tokens;
+
+
+import net.mightypork.rcalc.TokenList;
+import net.mightypork.rcalc.operations.Operation;
+
+
+/**
+ * Abstract operator token with one operand on right
+ * 
+ * @author Ondrej Hruska
+ */
+public abstract class TokenUnaryOperatorRight implements IOperatorToken {
+
+	/**
+	 * Convert to operation
+	 * 
+	 * @param operand operand
+	 * @return operation
+	 */
+	public abstract Operation toOperation(TokenList operand);
+}
diff --git a/src/net/mightypork/semestralka/CalculatorBatch.java b/src/net/mightypork/semestralka/CalculatorBatch.java
new file mode 100644
index 0000000..9e32f9d
--- /dev/null
+++ b/src/net/mightypork/semestralka/CalculatorBatch.java
@@ -0,0 +1,131 @@
+package net.mightypork.semestralka;
+
+
+import java.io.File;
+import java.io.FileReader;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Scanner;
+
+import net.mightypork.rcalc.ParseError;
+import net.mightypork.rcalc.RCalcSession;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Batch calculator (reads input from a file)
+ * 
+ * @author Ondrej Hruska
+ */
+public class CalculatorBatch implements Runnable {
+
+	/** Rcalc Session used by the calculator */
+	private RCalcSession session = new RCalcSession();
+
+	/** File to load the expressions from */
+	private File file;
+
+	/** Show results as fractions */
+	private boolean fractionalMode = true;
+
+	/** Flag that this calculator has been called from interactive mode */
+	private boolean fromInteractive;
+
+	//@formatter:off
+	private static final String introMessage = 
+			   "\nRational Calculator - file input mode\n"
+			 + "--------------------------------------\n"
+			 + "(c) Ondrej Hruska 2013\n"
+			 + "\n";
+	//@formatter:on
+
+	/**
+	 * Create a batch calculator
+	 * 
+	 * @param fileToLoad file to be executed
+	 */
+	public CalculatorBatch(File fileToLoad) {
+
+		this.file = fileToLoad;
+		this.fromInteractive = false;
+	}
+
+
+	/**
+	 * Create a batch calculator
+	 * 
+	 * @param fileToLoad file to be executed
+	 * @param calledFromInteractive called from the interactive calculator
+	 */
+	public CalculatorBatch(File fileToLoad, boolean calledFromInteractive) {
+
+		this.file = fileToLoad;
+		this.fromInteractive = calledFromInteractive;
+	}
+
+
+	/**
+	 * Set symbol table (share variables with other session)
+	 * 
+	 * @param symbolTable symbol table
+	 */
+	public void setSymbolTable(HashMap<String, Fraction> symbolTable) {
+
+		session.setSymbolTable(symbolTable);
+	}
+
+
+	@Override
+	public void run() {
+
+		if (!fromInteractive) {
+			System.out.println(introMessage);
+		}
+
+		System.out.println("\nFILE = " + file.getAbsolutePath() + "\n");
+
+		// input scanner
+		Scanner sc;
+		try {
+			sc = new Scanner(new FileReader(file));
+		} catch (IOException e) {
+			System.out.println("ERROR:\n\tFile not found.");
+			return;
+		}
+
+		System.out.println("--- File begin ---");
+
+		while (sc.hasNextLine()) {
+
+			String expr = sc.nextLine().trim();
+			System.out.println("\n> " + expr);
+
+			if (expr.equalsIgnoreCase("fractional") || expr.equalsIgnoreCase("decimal")) {
+
+				if (fractionalMode) {
+					System.out.println("[FRACTIONAL MODE OFF]");
+					fractionalMode = false;
+				} else {
+					System.out.println("[FRACTIONAL MODE ON]");
+					fractionalMode = true;
+				}
+
+			} else {
+				try {
+					Fraction result = session.evaluate(expr);
+					System.out.println("= " + (fractionalMode ? result.toString() : result.getDoubleValue()));
+				} catch (ParseError pe) {
+					System.out.println("PARSE ERROR:\n\t" + pe.getMessage());
+					System.out.println("\n--- Aborted ---");
+					return;
+				} catch (ArithmeticException ae) {
+					System.out.println("MATH ERROR:\n\t" + ae.getMessage());
+					System.out.println("\n--- Aborted ---");
+					return;
+				}
+			}
+		}
+
+		System.out.println("\n--- File end ---");
+	}
+}
diff --git a/src/net/mightypork/semestralka/CalculatorInteractive.java b/src/net/mightypork/semestralka/CalculatorInteractive.java
new file mode 100644
index 0000000..6bd82c8
--- /dev/null
+++ b/src/net/mightypork/semestralka/CalculatorInteractive.java
@@ -0,0 +1,192 @@
+package net.mightypork.semestralka;
+
+
+import java.io.File;
+import java.util.*;
+import java.util.Map.Entry;
+
+import net.mightypork.rcalc.ParseError;
+import net.mightypork.rcalc.RCalcSession;
+import net.mightypork.rcalc.numbers.Fraction;
+
+
+/**
+ * Interactive calculator
+ * 
+ * @author Ondrej Hruska
+ */
+public class CalculatorInteractive implements Runnable {
+
+	/** Rcalc Session used by the calculator */
+	private RCalcSession session = new RCalcSession();
+
+	/** Show results as fractions */
+	private boolean fractionalMode = true;
+
+	/** Command history */
+	private ArrayList<String> history = new ArrayList<String>();
+
+
+	//@formatter:off
+	private static final String introMessage = 
+		   "\nRational Calculator - interactive mode\n"
+		 + "--------------------------------------\n"
+		 + "(c) Ondrej Hruska 2013\n"
+		 + "\n"
+		 + "Type 'help' for more info.\n\n"
+		 + "Enter expression, 'exit' to quit.";
+	
+	
+	private static final String helpMessage = 
+		   "\n### HELP ###\n\n"
+		 + "Commands:\n"
+		 + "\thelp - show this help\n"
+		 + "\texit - quit the calculator\n"
+		 + "\tdebug - toggle debug mode (default off)\n"
+		 + "\tdecimal - toggle decimal/fractional output\n"
+		 + "\tvars - print a list of variables\n"
+		 + "\tload filename - execute commands from a file\n"
+		 + "\t\t(Expressions from the file can use/change variables)\n"
+		 + "\n"
+		 + "Mathematical operations, syntax\n"
+		 + "\tSupported: + - * / % ^ ! ( )\n"
+		 + "\tMultiplication sign can be omitted where it makes sense.\n"
+		 + "\tAlong with fractions, decimal-point format works too.\n"
+		 + "\tUse 'a/b' syntax to express a fraction.\n"
+		 + "\n"
+		 + "Variables\n"
+		 + "\tAssign a variable:\n"
+		 + "\t> name = expression\n\n"
+		 + "\tModify a variable:\n"
+		 + "\t> name += expression\n"
+		 + "\t> name -= expression\n"
+		 + "\t> name *= expression\n"
+		 + "\t> name /= expression\n"
+		 + "\t> name %= expression\n"
+		 + "\t> name ^= expression\n\n"
+		 + "\tYou can also use variable names in expressions.";
+	//@formatter:on
+
+
+	/**
+	 * Create an interactive calculator
+	 */
+	public CalculatorInteractive() {
+
+	}
+
+
+	@Override
+	public void run() {
+
+		System.out.println(introMessage);
+
+		// input scanner
+		Scanner sc = new Scanner(System.in);
+
+		while (true) {
+			System.out.print("\n> ");
+
+			// wait for input
+			while (!sc.hasNextLine()) {}
+
+			String expr = sc.nextLine().toLowerCase().trim();
+			
+			if (expr.equals("%")) { // repeat last expression
+				if (history.size() > 0) {
+					expr = history.get(history.size() - 1);
+					System.out.println("| " + expr);
+				} else {
+					System.out.println("No history available.");
+					continue;
+				}
+			}
+			
+			if (expr.equals("exit")) { // quit
+				System.out.println("Exit.");
+				return;
+
+			} else if (expr.equals("help")) { // show help
+				System.out.println(helpMessage);
+
+			} else if (expr.equals("debug")) { // toggle debug mode
+
+				if (session.isDebug()) {
+					System.out.println("[DEBUG OFF]");
+					session.setDebug(false);
+				} else {
+					System.out.println("[DEBUG ON]");
+					session.setDebug(true);
+				}
+
+			} else if (expr.equals("decimal")) { // toggle decimal/fractional output mode
+
+				if (fractionalMode) {
+					System.out.println("[FRACTIONAL MODE OFF]");
+					fractionalMode = false;
+				} else {
+					System.out.println("[FRACTIONAL MODE ON]");
+					fractionalMode = true;
+				}
+
+			} else if (expr.startsWith("load ")) { // load and execute expressions from file
+				expr = expr.replace("load ", "");
+
+				CalculatorBatch cb = new CalculatorBatch(new File(expr), true);
+				cb.setSymbolTable(session.getSymbolTable());
+
+				cb.run();
+
+			} else if (expr.equals("vars")) { // list variables
+
+				HashMap<String, Fraction> vars = (session.getSymbolTable());
+
+				Map<String, Fraction> varsSorted = sortByKeys(vars);
+
+				System.out.println("\nVariables\n");
+
+				for (Entry<String, Fraction> entry : varsSorted.entrySet()) {
+					System.out.println("\t" + entry.getKey() + " = " + entry.getValue());
+				}
+
+			} else { // evaluate an expression
+
+				try {
+					Fraction result = session.evaluate(expr);
+					if (result == null) {
+						continue;
+					}
+					history.add(expr);
+					System.out.println("= " + (fractionalMode ? result.toString() : result.getDoubleValue()));
+				} catch (ParseError pe) {
+					System.out.println("PARSE ERROR:\n\t" + pe.getMessage());
+				} catch (ArithmeticException ae) {
+					System.out.println("MATH ERROR:\n\t" + ae.getMessage());
+				}
+			}
+
+		}
+	}
+
+
+	/**
+	 * Sort a map by keys, maintaining key-value pairs.<br>
+	 * Source: StackOverflow.com
+	 * 
+	 * @param map map to be sorted
+	 * @return linked hash map with sorted entries
+	 */
+	@SuppressWarnings({ "rawtypes", "unchecked" })
+	private static <K extends Comparable, V> Map<K, V> sortByKeys(Map<K, V> map) {
+
+		List<K> keys = new LinkedList<K>(map.keySet());
+		Collections.sort(keys);
+
+		Map<K, V> sortedMap = new LinkedHashMap<K, V>();
+		for (K key : keys) {
+			sortedMap.put(key, map.get(key));
+		}
+
+		return sortedMap;
+	}
+}
diff --git a/src/net/mightypork/semestralka/Main.java b/src/net/mightypork/semestralka/Main.java
new file mode 100644
index 0000000..b5069be
--- /dev/null
+++ b/src/net/mightypork/semestralka/Main.java
@@ -0,0 +1,36 @@
+package net.mightypork.semestralka;
+
+
+import java.io.File;
+
+
+/**
+ * Application main class
+ * 
+ * @author Ondrej Hruska
+ */
+public class Main {
+
+	/**
+	 * Program entry point
+	 * 
+	 * @param args command line arguemnts
+	 */
+	public static void main(String[] args) {
+
+		if (args.length == 0 || (args.length == 1 && args[0].equals("-i"))) {
+
+			Runnable task = new CalculatorInteractive();
+			task.run();
+
+		} else if (args.length == 1) {
+
+			Runnable task = new CalculatorBatch(new File(args[0]));
+			task.run();
+
+		}
+
+	}
+
+
+}
diff --git a/src/net/mightypork/semestralka/Tests.java b/src/net/mightypork/semestralka/Tests.java
new file mode 100644
index 0000000..b852435
--- /dev/null
+++ b/src/net/mightypork/semestralka/Tests.java
@@ -0,0 +1,56 @@
+package net.mightypork.semestralka;
+
+
+import net.mightypork.rcalc.RCalc;
+
+
+/**
+ * RCalc unit tests
+ * 
+ * @author Ondrej Hruska
+ */
+public class Tests {
+
+	/**
+	 * Run the tests
+	 */
+	public static void run() {
+
+		RCalc rc = new RCalc();
+		rc.setDebug(true);
+
+		//@formatter:off
+		String[] testCases = new String[] {
+				// Parser unit test
+				"57**3 + -7^2 + (-7)^2", // power
+				"(13*7)(99^2) * 4(12/7) + (17-8/2)13 + (4/3)*5", // implicit multiplication
+				"(1-1)(1--1)(1---1)(1----1)(1--+-+-+++--+-+1)(1--+-+-+-+-----1)(5*-1)", // minus, plus
+				"-(15/2)+(72*43-2)-(12+1)", // minus with parentheses
+				"+34-(--8+2*+13)", // + at beginning of scope
+				// misc
+				"23%(6/5)",
+				"53/(5-4-1)",
+				"100!",
+				"24/4/3",
+				"(10+1)(15-3)",
+				"13(55-3/12)^2",
+				"(1/2)^-2",
+				"13^(1/2)", // should fail
+				"(1/2)*(3/4)",
+				"(1/2)/(3/4)", // compound fraction
+		};
+		//@formatter:on
+
+		for (String expr : testCases) {
+			System.out.println("\n\n###### test case begin ######");
+
+			try {
+				System.out.println("IN: " + expr);
+				System.out.println("OUT: " + rc.evaluate(expr));
+			} catch (Exception e) {
+				System.out.println("ERROR: " + e.getMessage());
+			}
+		}
+
+	}
+}