diff --git a/src/net/mightypork/rcalc/IToken.java b/src/net/mightypork/rcalc/IToken.java
index 54a28f1..2125992 100644
--- a/src/net/mightypork/rcalc/IToken.java
+++ b/src/net/mightypork/rcalc/IToken.java
@@ -7,5 +7,9 @@ package net.mightypork.rcalc;
  * @author Ondrej Hruska
  */
 public interface IToken {
-
+	/**
+	 * Wrap this token in a tokenList (return itself if already instance of a TokenList)
+	 * @return the wrapping TokenList
+	 */
+	public TokenList wrapInTokenList();
 }
diff --git a/src/net/mightypork/rcalc/RCalcSession.java b/src/net/mightypork/rcalc/RCalcSession.java
index 92c779e..7464c4c 100644
--- a/src/net/mightypork/rcalc/RCalcSession.java
+++ b/src/net/mightypork/rcalc/RCalcSession.java
@@ -76,7 +76,7 @@ public class RCalcSession implements IDebugable {
 
 		if (expression.length() == 0) return null; // no operation
 
-		expression.replace(":=", "="); // normalize assignment sign
+		expression = expression.replace(":=", "="); // normalize assignment sign
 
 		String assignedVariable = null;
 		String assignmentOperation = "";
diff --git a/src/net/mightypork/rcalc/TokenList.java b/src/net/mightypork/rcalc/TokenList.java
index 60fa0a7..9f11a00 100644
--- a/src/net/mightypork/rcalc/TokenList.java
+++ b/src/net/mightypork/rcalc/TokenList.java
@@ -35,6 +35,15 @@ public class TokenList extends ArrayList<IToken> implements IToken {
 	}
 
 
+	/**
+	 * Create a tokenList with single item
+	 * @param token the item
+	 */
+	public TokenList(IToken token) {
+		add(token);
+	}
+
+
 	/**
 	 * Parse the token list.<br>
 	 * After running this method, the list is typically reduced to a single
@@ -121,29 +130,12 @@ public class TokenList extends ArrayList<IToken> implements IToken {
 
 				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);
-				}
+				// get operands
+				TokenList leftArg = get(pos - 1).wrapInTokenList();
+				TokenList rightArg = get(pos + 1).wrapInTokenList();
 
 				// build an operation
-				Operation op = opToken.toOperation(leftTL, rightTL);
+				Operation op = opToken.toOperation(leftArg, rightArg);
 
 				// discard used tokens
 				subList(pos - 1, pos + 2).clear();
@@ -156,20 +148,11 @@ public class TokenList extends ArrayList<IToken> implements IToken {
 
 				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);
-				}
+				// get operand
+				TokenList leftArg = get(pos - 1).wrapInTokenList();
 
 				// build an operation
-				Operation op = opToken.toOperation(leftTL);
+				Operation op = opToken.toOperation(leftArg);
 
 				// discard used tokens
 				subList(pos - 1, pos + 1).clear();
@@ -183,19 +166,10 @@ public class TokenList extends ArrayList<IToken> implements IToken {
 				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);
-				}
+				TokenList rightArg = get(pos + 1).wrapInTokenList();
 
 				// build an operation
-				Operation op = opToken.toOperation(rightTL);
+				Operation op = opToken.toOperation(rightArg);
 
 				// discard used tokens
 				subList(pos, pos + 2).clear();
@@ -265,4 +239,10 @@ public class TokenList extends ArrayList<IToken> implements IToken {
 	}
 
 
+	@Override
+	public TokenList wrapInTokenList() {
+		return this;
+	}
+
+
 }
diff --git a/src/net/mightypork/rcalc/numbers/Fraction.java b/src/net/mightypork/rcalc/numbers/Fraction.java
index 68d10bb..de4f595 100644
--- a/src/net/mightypork/rcalc/numbers/Fraction.java
+++ b/src/net/mightypork/rcalc/numbers/Fraction.java
@@ -5,6 +5,7 @@ import java.math.BigInteger;
 
 import net.mightypork.rcalc.IEvaluableToken;
 import net.mightypork.rcalc.ParseError;
+import net.mightypork.rcalc.TokenList;
 
 
 /**
@@ -461,4 +462,10 @@ public class Fraction implements IEvaluableToken {
 		return new Fraction(result, BigInteger.ONE);
 	}
 
+
+	@Override
+	public TokenList wrapInTokenList() {
+		return new TokenList(this);
+	}
+
 }
diff --git a/src/net/mightypork/rcalc/operations/Operation.java b/src/net/mightypork/rcalc/operations/Operation.java
index cd3254d..3f45f7a 100644
--- a/src/net/mightypork/rcalc/operations/Operation.java
+++ b/src/net/mightypork/rcalc/operations/Operation.java
@@ -2,6 +2,7 @@ package net.mightypork.rcalc.operations;
 
 
 import net.mightypork.rcalc.IEvaluableToken;
+import net.mightypork.rcalc.TokenList;
 import net.mightypork.rcalc.numbers.Fraction;
 
 
@@ -14,4 +15,9 @@ public abstract class Operation implements IEvaluableToken {
 
 	@Override
 	public abstract Fraction evaluate();
+	
+	@Override
+	public TokenList wrapInTokenList() {
+		return new TokenList(this);
+	}
 }
diff --git a/src/net/mightypork/rcalc/tokens/TokenBinaryOperator.java b/src/net/mightypork/rcalc/tokens/TokenBinaryOperator.java
index 7709e2c..25e8763 100644
--- a/src/net/mightypork/rcalc/tokens/TokenBinaryOperator.java
+++ b/src/net/mightypork/rcalc/tokens/TokenBinaryOperator.java
@@ -10,7 +10,7 @@ import net.mightypork.rcalc.operations.Operation;
  * 
  * @author Ondrej Hruska
  */
-public abstract class TokenBinaryOperator implements IOperatorToken {
+public abstract class TokenBinaryOperator extends TokenOperator {
 
 	/**
 	 * Convert to operation
diff --git a/src/net/mightypork/rcalc/tokens/TokenOperator.java b/src/net/mightypork/rcalc/tokens/TokenOperator.java
new file mode 100644
index 0000000..954cc07
--- /dev/null
+++ b/src/net/mightypork/rcalc/tokens/TokenOperator.java
@@ -0,0 +1,12 @@
+package net.mightypork.rcalc.tokens;
+
+import net.mightypork.rcalc.TokenList;
+
+public class TokenOperator implements IOperatorToken {
+
+	@Override
+	public TokenList wrapInTokenList() {
+		return new TokenList(this);
+	}
+
+}
diff --git a/src/net/mightypork/rcalc/tokens/TokenParenthesisLeft.java b/src/net/mightypork/rcalc/tokens/TokenParenthesisLeft.java
index 9e78600..91be265 100644
--- a/src/net/mightypork/rcalc/tokens/TokenParenthesisLeft.java
+++ b/src/net/mightypork/rcalc/tokens/TokenParenthesisLeft.java
@@ -2,6 +2,7 @@ package net.mightypork.rcalc.tokens;
 
 
 import net.mightypork.rcalc.IToken;
+import net.mightypork.rcalc.TokenList;
 
 
 /**
@@ -17,4 +18,9 @@ public class TokenParenthesisLeft implements IToken {
 		return "(";
 	}
 
+	@Override
+	public TokenList wrapInTokenList() {
+		throw new RuntimeException("Cannot wrap a parenthesis in a TokenList!");
+	}
+
 }
diff --git a/src/net/mightypork/rcalc/tokens/TokenParenthesisRight.java b/src/net/mightypork/rcalc/tokens/TokenParenthesisRight.java
index 73eca62..41ef164 100644
--- a/src/net/mightypork/rcalc/tokens/TokenParenthesisRight.java
+++ b/src/net/mightypork/rcalc/tokens/TokenParenthesisRight.java
@@ -2,6 +2,7 @@ package net.mightypork.rcalc.tokens;
 
 
 import net.mightypork.rcalc.IToken;
+import net.mightypork.rcalc.TokenList;
 
 
 /**
@@ -17,4 +18,8 @@ public class TokenParenthesisRight implements IToken {
 		return ")";
 	}
 
+	@Override
+	public TokenList wrapInTokenList() {
+		throw new RuntimeException("Cannot wrap a parenthesis in a TokenList!");
+	}
 }
diff --git a/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorLeft.java b/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorLeft.java
index e74d07e..3021889 100644
--- a/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorLeft.java
+++ b/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorLeft.java
@@ -10,7 +10,7 @@ import net.mightypork.rcalc.operations.Operation;
  * 
  * @author Ondrej Hruska
  */
-public abstract class TokenUnaryOperatorLeft implements IOperatorToken {
+public abstract class TokenUnaryOperatorLeft extends TokenOperator {
 
 	/**
 	 * Convert to operation
diff --git a/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorRight.java b/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorRight.java
index 2812ced..1077202 100644
--- a/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorRight.java
+++ b/src/net/mightypork/rcalc/tokens/TokenUnaryOperatorRight.java
@@ -10,7 +10,7 @@ import net.mightypork.rcalc.operations.Operation;
  * 
  * @author Ondrej Hruska
  */
-public abstract class TokenUnaryOperatorRight implements IOperatorToken {
+public abstract class TokenUnaryOperatorRight extends TokenOperator {
 
 	/**
 	 * Convert to operation