Exploded the exp4j source into our src/ directory. This allows us to more easily modify changes we make to the source. I inlined one call to Arrays.copyOf.

android/.classpath

@@ -7,6 +7,5 @@
 	<classpathentry kind="con" path="com.android.ide.eclipse.adt.ANDROID_FRAMEWORK"/>
 	<classpathentry kind="con" path="com.android.ide.eclipse.adt.LIBRARIES"/>
 	<classpathentry kind="lib" path="libs/android-support-v4.jar"/>
-	<classpathentry kind="lib" path="libs/exp4j-rdg.jar"/>
 	<classpathentry kind="output" path="bin/classes"/>
 </classpath>

core/.classpath

@@ -30,6 +30,5 @@
 	<classpathentry kind="lib" path="lib/jogl/gluegen-rt.jar"/>
 	<classpathentry kind="lib" path="lib/jogl/jogl.all.jar"/>
 	<classpathentry kind="lib" path="lib/OrangeExtensions-1.2.jar"/>
-	<classpathentry kind="lib" path="lib/exp4j-rdg.jar"/>
 	<classpathentry kind="output" path="bin"/>
 </classpath>

core/build.xml

@@ -112,7 +112,6 @@
 				<attribute name="Main-Class" value="${main-class}"/>
 				<attribute name="SplashScreen-Image" value="pix/splashscreen.png"/>
 			</manifest>
-			<zipfileset src="lib/exp4j-rdg.jar" />
 		</jar>
 	</target>
 

core/src/de/congrace/exp4j/AbstractExpression.java

@@ -0,0 +1,77 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.text.NumberFormat;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Abstract base class for mathematical expressions
+ * 
+ * @author fas@congrace.de
+ */
+abstract class AbstractExpression {
+	private final String expression;
+	private final Token[] tokens;
+	private final String[] variableStrings;
+	private final NumberFormat numberFormat = NumberFormat.getInstance();
+
+	/**
+	 * Construct a new {@link AbstractExpression}
+	 * 
+	 * @param expression
+	 *            the mathematical expression to be used
+	 * @param tokens
+	 *            the {@link Token}s in the expression
+	 * @param variableNames
+	 *            an array of variable names which are used in the expression
+	 */
+	AbstractExpression(String expression, Token[] tokens, String[] variableStrings) {
+		this.expression = expression;
+		this.tokens = tokens;
+		this.variableStrings = variableStrings;
+	}
+
+	/**
+	 * get the mathematical expression {@link String}
+	 * 
+	 * @return the expression
+	 */
+	public String getExpression() {
+		return expression;
+	}
+
+	/**
+	 * get the used {@link NumberFormat}
+	 * 
+	 * @return the used {@link NumberFormat}
+	 */
+	public NumberFormat getNumberFormat() {
+		return numberFormat;
+	}
+
+	/**
+	 * get the {@link Token}s
+	 * 
+	 * @return the array of {@link Token}s
+	 */
+	Token[] getTokens() {
+		return tokens;
+	}
+	
+}

core/src/de/congrace/exp4j/Calculable.java

@@ -0,0 +1,31 @@
+package de.congrace.exp4j;
+
+/**
+ * This is the basic result class of the exp4j {@link ExpressionBuilder}
+ * 
+ * @author ruckus
+ * 
+ */
+public interface Calculable {
+	/**
+	 * calculate the result of the expression
+	 * 
+	 * @return the result of the calculation
+	 */
+	public Variable calculate();
+
+	/**
+	 * return the expression in reverse polish postfix notation
+	 * 
+	 * @return the expression used to construct this {@link Calculable}
+	 */
+	public String getExpression();
+
+	/**
+	 * set a variable value for the calculation
+	 * 
+	 * @param value
+	 *            the value of the variable
+	 */
+	public void setVariable(Variable var);
+}

core/src/de/congrace/exp4j/CalculationToken.java

@@ -0,0 +1,76 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.util.Arrays;
+import java.util.Stack;
+
+abstract class CalculationToken extends Token {
+
+	CalculationToken(String value) {
+		super(value);
+	}
+
+	abstract void mutateStackForCalculation(Stack<Variable> stack, VariableSet variables);
+
+	/*
+	 * Given an array of variables, check if any are arrays and if so expand any other of the given variables to arrays of the same length.
+	 * Doubles are turned into arrays of all the same value as original. Arrays of other lengths are padded with zeros. 
+	 */
+	public Variable[] expandVariables(Variable[] values){
+		// Check if any variables have preferred representation as arrays
+		int maxLength = 0;
+		for (Variable v : values){
+			if (v.getPrimary() == Variable.Primary.ARRAY && v.getArrayValue().length > maxLength){
+				maxLength = v.getArrayValue().length;
+			}
+		}
+		
+		// if necessary, expand any non-array variables to maximum length
+		if (maxLength > 0) {
+			for (int n = 0; n<values.length; n++){
+				Variable v = values[n];
+				if (v.getPrimary() == Variable.Primary.DOUBLE){
+					double[] a = new double[maxLength];
+					Arrays.fill(a, v.getDoubleValue());
+					values[n] = new Variable(v.getName(), a);
+				}
+				else if (v.getPrimary() == Variable.Primary.ARRAY){
+					// inlining Arrays.copyOf to provide compatibility with Froyo
+					double[] a = new double[maxLength];
+					int i = 0;
+					double[] vArrayValues = v.getArrayValue();
+					while( i < vArrayValues.length && i < maxLength ) {
+						a[i] = vArrayValues[i];
+						i++;
+					}
+					while ( i< maxLength ) {
+						a[i] = 0.0;
+						i++;
+					}
+					values[n] = new Variable(v.getName(), a);
+				} 
+				else {
+					// Should not happen, if it does return invalid variable
+					return new Variable[] { new Variable("Invalid")};
+				}
+			}
+		}
+		
+		return values;
+	}
+}

core/src/de/congrace/exp4j/CommandlineInterpreter.java

@@ -0,0 +1,59 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+/**
+ * Simple commandline interpreter for mathematical expressions the interpreter
+ * takes a mathematical expressions as a {@link String} argument, evaluates it
+ * and prints out the result.
+ * 
+ * 
+ * <pre>
+ * java de.congrace.exp4j.CommandlineInterpreter "2 * log(2.2223) - ((2-3.221) * 14.232^2)"
+ * > 248.91042049521056
+ * </pre>
+ * 
+ * @author fas@congrace.de
+ * 
+ */
+public class CommandlineInterpreter {
+	private static void calculateExpression(String string) {
+		try {
+			final PostfixExpression pe = PostfixExpression.fromInfix(string);
+			System.out.println(pe.calculate());
+		} catch (UnparsableExpressionException e) {
+			e.printStackTrace();
+		} catch (UnknownFunctionException e) {
+			e.printStackTrace();
+		}
+	}
+
+	public static void main(String[] args) {
+		if (args.length != 1) {
+			printUsage();
+		} else {
+			calculateExpression(args[0]);
+		}
+	}
+
+	private static void printUsage() {
+		final StringBuilder usage = new StringBuilder();
+		usage.append("Commandline Expression Parser\n\n").append("Example: ").append("\n").append("java -jar exp4j.jar \"2.12 * log(23) * (12 - 4)\"\n\n")
+				.append("written by fas@congrace.de");
+		System.err.println(usage.toString());
+	}
+}

core/src/de/congrace/exp4j/CustomFunction.java

@@ -0,0 +1,90 @@
+package de.congrace.exp4j;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Stack;
+
+import de.congrace.exp4j.FunctionToken.Function;
+
+/**
+ * this classed is used to create custom functions for exp4j<br/>
+ * <br/>
+ * <b>Example</b><br/>
+ * <code><pre>{@code 
+ * CustomFunction fooFunc = new CustomFunction("foo") {
+ * 		public double applyFunction(double value) {
+ * 			return value*Math.E;
+ * 		}
+ * };
+ * double varX=12d;
+ * Calculable calc = new ExpressionBuilder("foo(x)").withCustomFunction(fooFunc).withVariable("x",varX).build();
+ * assertTrue(calc.calculate() == Math.E * varX);
+ * }</pre></code>
+ * 
+ * @author ruckus
+ * 
+ */
+public abstract class CustomFunction extends CalculationToken {
+    private int argc=1;
+
+	/**
+	 * create a new single value input CustomFunction with a set name
+	 * 
+	 * @param value
+	 *            the name of the function (e.g. foo)
+	 */
+	protected CustomFunction(String value) throws InvalidCustomFunctionException{
+		super(value);
+		for (Function f:Function.values()) {
+			if (value.equalsIgnoreCase(f.toString())){
+				throw new InvalidCustomFunctionException(value + " is already reserved as a function name");
+			}
+		}
+	}
+
+    /**
+     * create a new single value input CustomFunction with a set name
+     * 
+     * @param value
+     *            the name of the function (e.g. foo)
+     */
+    protected CustomFunction(String value,int argumentCount) throws InvalidCustomFunctionException{
+        super(value);
+        this.argc=argumentCount;
+        for (Function f:Function.values()) {
+            if (value.equalsIgnoreCase(f.toString())){
+                throw new InvalidCustomFunctionException(value + " is already reserved as a function name");
+            }
+        }
+    }
+
+    /**
+	 * apply the function to a value
+	 * 
+	 * @param values
+	 *            the values to which the function should be applied.
+	 * @return the function value
+	 */
+	public abstract Variable applyFunction(List<Variable> vars);
+
+    @Override
+	void mutateStackForCalculation(Stack<Variable> stack, VariableSet variables) {
+	    List<Variable> args = new ArrayList<Variable>(argc);
+	    for (int i=0; i < argc; i++) {
+	    	args.add(i, stack.pop() );
+	    }
+	    Collections.reverse(args); // Put elements in logical order
+	    
+		stack.push(this.applyFunction(args));
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		operatorStack.push(this);
+	}
+	public int getArgumentCount() {
+	    return argc;
+	}
+}

core/src/de/congrace/exp4j/Example.java

@@ -0,0 +1,77 @@
+package de.congrace.exp4j;
+
+import java.util.List;
+
+public class Example {
+
+	public static void main(String[] args) throws UnknownFunctionException, UnparsableExpressionException, InvalidCustomFunctionException {
+
+		// Test 1
+		// ======
+		
+		Calculable calc1 = new ExpressionBuilder("x * y - 2").withVariableNames("x", "y").build();
+		calc1.setVariable(new Variable("x", 1.2));
+		calc1.setVariable(new Variable("y", 2.2));
+		
+		System.out.println(calc1.calculate().toString());
+		//double result = calc1.calculate().getDoubleValue();
+		//System.out.println(result);
+			
+		// Test 2
+		// ======
+		
+		// A function which calculates the mean of an array and scales it
+		CustomFunction meanFn = new CustomFunction("mean",2) {
+		    public Variable applyFunction(List<Variable> vars) {
+		        
+		    	double[] vals;
+		    	double scale;
+		    	
+		    	try{
+		    		vals = vars.get(0).getArrayValue();
+		    		scale = vars.get(1).getDoubleValue();
+		    	} catch (Exception e) {
+		    		return new Variable("Invalid");
+		    	}
+		    	
+		    	double subtotal = 0;
+		    	for (int i = 0; i < vals.length; i++ ){
+		    		subtotal += vals[i];
+		    	}
+		    	
+		    	subtotal = scale * subtotal / vals.length;
+		        return new Variable("double MEAN result, ", subtotal);
+		        
+		    }
+		};
+				
+		ExpressionBuilder b = new ExpressionBuilder("mean(x,y)");
+		b.withCustomFunction(meanFn);
+		b.withVariable(new Variable("x", new double[] {1.1,2,10,3,2.4,10.2}));
+		b.withVariable(new Variable("y", 2));
+		Calculable calc2 = b.build();
+		
+		System.out.println( calc2.calculate().toString() );
+		
+		// Test 3
+		// ======
+		
+		Calculable calc3 = new ExpressionBuilder("x * y - 2").withVariableNames("x", "y").build();
+		calc3.setVariable(new Variable("x", new double[]{1.2, 10, 20, 15}));
+		calc3.setVariable(new Variable("y", new double[]{2.2, 5.2, 12, 9 }));
+		
+		//double result3 = calc3.calculate().getDoubleValue();
+		System.out.println(calc3.calculate().toString());
+		
+
+		// Test 4
+		// ======
+				
+		Calculable calc4 = new ExpressionBuilder("log10(sqrt(x) * abs(y))").withVariableNames("x", "y").build();
+		calc4.setVariable(new Variable("x", new double[]{1.2, 10, 10, 15}));
+		calc4.setVariable(new Variable("y", new double[]{2.2, -5.2, 5.2, 9 }));
+		
+		//double result3 = calc3.calculate().getDoubleValue();
+		System.out.println(calc4.calculate().toString());		
+	}
+}

core/src/de/congrace/exp4j/ExpressionBuilder.java

@@ -0,0 +1,135 @@
+package de.congrace.exp4j;
+
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * This is Builder implementation for the exp4j API used to create a Calculable
+ * instance for the user
+ * 
+ * @author ruckus
+ * 
+ */
+public class ExpressionBuilder {
+	private VariableSet variables = new VariableSet();
+	private final Set<CustomFunction> customFunctions = new HashSet<CustomFunction>();
+
+	private String expression;
+
+	/**
+	 * Create a new ExpressionBuilder
+	 * 
+	 * @param expression
+	 *            the expression to evaluate
+	 */
+	public ExpressionBuilder(String expression) {
+		this.expression = expression;
+	}
+	
+	/**
+	 * build a new {@link Calculable} from the expression using the supplied
+	 * variables
+	 * 
+	 * @return the {@link Calculable} which can be used to evaluate the
+	 *         expression
+	 * @throws UnknownFunctionException
+	 *             when an unrecognized function name is used in the expression
+	 * @throws UnparsableExpressionException
+	 *             if the expression could not be parsed
+	 */
+	public Calculable build() throws UnknownFunctionException, UnparsableExpressionException {
+		if (expression.indexOf('=') == -1 && !variables.isEmpty()) {
+
+			// User supplied an expression without leading "f(...)="
+			// so we just append the user function to a proper "f()="
+			// for PostfixExpression.fromInfix()
+			StringBuilder function = new StringBuilder("f(");
+			for (String name : variables.getVariableNames()) {
+				function.append(name).append(',');
+			}
+			expression = function.deleteCharAt(function.length() - 1).toString() + ")=" + expression;
+		}
+		// create the PostfixExpression and return it as a Calculable
+		PostfixExpression delegate = PostfixExpression.fromInfix(expression, customFunctions);
+		for (Variable var : variables ) {			
+			delegate.setVariable(var);	
+			for (CustomFunction fn:customFunctions){
+				if (fn.getValue().equalsIgnoreCase(var.getName())){
+					throw new UnparsableExpressionException("variable '" + var + "' cannot have the same name as a custom function " + fn.getValue());
+				}
+			}
+		}
+		return delegate;
+	}
+
+	/**
+	 * add a custom function instance for the evaluator to recognize
+	 * 
+	 * @param function
+	 *            the {@link CustomFunction} to add
+	 * @return the {@link ExpressionBuilder} instance
+	 */
+	public ExpressionBuilder withCustomFunction(CustomFunction function) {
+		customFunctions.add(function);
+		return this;
+	}
+
+	public ExpressionBuilder withCustomFunctions(Collection<CustomFunction> functions) {
+		customFunctions.addAll(functions);
+		return this;
+	}
+
+	/**
+	 * set the value for a variable
+	 * 
+	 * @param variableName
+	 *            the variable name e.g. "x"
+	 * @param value
+	 *            the value e.g. 2.32d
+	 * @return the {@link ExpressionBuilder} instance
+	 */
+	public ExpressionBuilder withVariable(Variable value) {
+		variables.add(value);
+		return this;
+	}
+
+	/*
+	 * Provided for backwards compatibility
+	 */
+	@Deprecated
+	public ExpressionBuilder withVariable(String variableName, double value) {
+		variables.add(new Variable(variableName, value));
+		return this;
+	}
+		
+	/**
+	 * set the variables names used in the expression without setting their
+	 * values. Usefull for building an expression before you know the variable values.
+	 * 
+	 * @param variableNames
+	 *            vararg {@link String} of the variable names used in the
+	 *            expression
+	 * @return the ExpressionBuilder instance
+	 */
+	
+	public ExpressionBuilder withVariableNames(String... variableNames) {
+		for (String name : variableNames) {
+			variables.add( new Variable(name, Double.NaN) );
+		}
+		return this;
+	}
+	
+
+	/**
+	 * set the values for variables
+	 * 
+	 * @param variableMap
+	 *            a map of variable names to variable values
+	 * @return the {@link ExpressionBuilder} instance
+	 */
+	public ExpressionBuilder withVariables(VariableSet variables) {
+		this.variables = variables;
+		return this;
+	}
+}

core/src/de/congrace/exp4j/FunctionSeparatorToken.java

@@ -0,0 +1,17 @@
+package de.congrace.exp4j;
+
+import java.util.Stack;
+
+public class FunctionSeparatorToken extends Token{
+    public FunctionSeparatorToken() {
+        super(",");
+    }
+    @Override
+    void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+        Token token;
+        while (!((token=operatorStack.peek()) instanceof ParenthesisToken) && !token.getValue().equals("(")){
+            output.append(operatorStack.pop().getValue()).append(" ");
+        }
+    }
+
+}

core/src/de/congrace/exp4j/FunctionToken.java

@@ -0,0 +1,161 @@
+/*
+Copyright 2011 frank asseg
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.util.Stack;
+
+/**
+ * A {@link Token} for functions
+ * 
+ * @author fas@congrace.de
+ * 
+ */
+class FunctionToken extends CalculationToken {
+	/**
+	 * the functionNames that can be used in an expression
+	 * 
+	 * @author ruckus
+	 * 
+	 */
+	enum Function {
+		ABS, ACOS, ASIN, ATAN, CBRT, CEIL, COS, COSH, EXP, EXPM1, FLOOR, ROUND, RANDOM, LOG, SIN, SINH, SQRT, TAN, TANH, LOG10
+	}
+
+	private Function function;
+
+	/**
+	 * construct a new {@link FunctionToken}
+	 * 
+	 * @param value
+	 *            the name of the function
+	 * @throws UnknownFunctionException
+	 *             if an unknown function name is encountered
+	 */
+	FunctionToken(String value) throws UnknownFunctionException {
+		super(value);
+		try {
+			function = Function.valueOf(value.toUpperCase());
+		} catch (IllegalArgumentException e) {
+			throw new UnknownFunctionException(value);
+		}
+		if (function == null) {
+			throw new UnknownFunctionException(value);
+		}
+	}
+
+	/**
+	 * apply a function to a variable
+	 * 
+	 * @param x
+	 *            the value the function should be applied to
+	 * @return the result of the function
+	 */
+	public Variable applyFunction(Variable var) {
+		
+		// The names here are strictly unused, but are useful for debugging
+		String name = function.name() + " result (#"+var.hashCode()+"), ";
+		
+		switch (var.getPrimary()) {
+			case DOUBLE:
+				name = "double "+name;
+				double x = var.getDoubleValue();
+				return new Variable(name, applyFunction(x) );	
+			
+			case ARRAY:
+				name = "array "+name;
+				double[] input = var.getArrayValue();
+				double[] result = new double[input.length];
+				for (int i = 0; i < input.length; i++){
+					result[i] = applyFunction(input[i]);
+				}
+				return new Variable(name, result);
+			
+			default:
+				return new Variable("Invalid");
+		}
+	}
+	
+	/*
+	 * The actual function application on a double
+	 */
+	private double applyFunction(double x){
+		switch (function) {
+		case ABS:
+			return Math.abs(x);
+		case ACOS:
+			return Math.acos(x);
+		case ASIN:
+			return Math.asin(x);
+		case ATAN:
+			return Math.atan(x);
+		case CBRT:
+			return Math.cbrt(x);
+		case CEIL:
+			return Math.ceil(x);
+		case COS:
+			return Math.cos(x);
+		case COSH:
+			return Math.cosh(x);
+		case EXP:
+			return Math.exp(x);
+		case EXPM1:
+			return Math.expm1(x);
+		case FLOOR:
+			return Math.floor(x);
+		case ROUND:
+			return Math.round(x);
+		case RANDOM:
+			return Math.random()*x;
+		case LOG:
+			return Math.log(x);
+		case LOG10:
+			return Math.log10(x);
+		case SIN:
+			return Math.sin(x);
+		case SINH:
+			return Math.sinh(x);
+		case SQRT:
+			return Math.sqrt(x);
+		case TAN:
+			return Math.tan(x);
+		case TANH:
+			return Math.tanh(x);
+		default:
+			return Double.NaN; // should not happen ;)
+		}
+	}
+
+	/**
+	 * 
+	 * get the {@link Function}
+	 * 
+	 * @return the correspoding {@link Function}
+	 */
+	Function getFunction() {
+		return function;
+	}
+
+	@Override
+	void mutateStackForCalculation(Stack<Variable> stack, VariableSet variableValues) {
+		stack.push(this.applyFunction(stack.pop()));
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		operatorStack.push(this);
+	}
+}

core/src/de/congrace/exp4j/InfixTranslator.java

@@ -0,0 +1,109 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.util.Set;
+import java.util.Stack;
+
+/**
+ * Translate a mathematical expression in human readable infix notation to a
+ * Reverse Polish Notation (postfix) expression for easier parsing. by
+ * implementing the shunting yard algorithm by dijkstra
+ * 
+ * @author fas@congrace.de
+ */
+class InfixTranslator {
+
+	private static String substituteUnaryOperators(String expr) {
+		final StringBuilder exprBuilder = new StringBuilder(expr.length());
+		final char[] data = expr.toCharArray();
+		char lastChar = ' ';
+		for (int i = 0; i < expr.length(); i++) {
+			if (exprBuilder.length() > 0) {
+				lastChar = exprBuilder.charAt(exprBuilder.length() - 1);
+			}
+			final char c = data[i];
+			switch (c) {
+			case '+':
+				if (i > 0 && lastChar != '(' && !(OperatorToken.isOperator(lastChar))) {
+					exprBuilder.append(c);
+				}
+				break;
+			case '-':
+				if (i > 0 && lastChar != '(' && !(OperatorToken.isOperator(lastChar))) {
+					exprBuilder.append(c);
+				} else {
+					exprBuilder.append('#');
+				}
+				break;
+			default:
+				if (!Character.isWhitespace(c)) {
+					exprBuilder.append(c);
+				}
+			}
+		}
+		return exprBuilder.toString();
+	}
+
+	/**
+	 * Delegation method for simple expression without variables or custom
+	 * functions
+	 * 
+	 * @param infixExpression
+	 *            the infix expression to be translated
+	 * @return translated RNP postfix expression
+	 * @throws UnparsableExpressionException
+	 *             when the expression is invalid
+	 * @throws UnknownFunctionException
+	 *             when an unknown function has been used in the input.
+	 */
+	static String toPostfixExpression(String infixExpression) throws UnparsableExpressionException, UnknownFunctionException {
+		return toPostfixExpression(infixExpression, null, null);
+	}
+
+	/**
+	 * implement the shunting yard algorithm
+	 * 
+	 * @param infixExpression
+	 *            the human readable expression which should be translated to
+	 *            RPN
+	 * @param variableNames
+	 *            the variable names used in the expression
+	 * @param customFunctions
+	 *            the CustomFunction implementations used
+	 * @return the expression in postfix format
+	 * @throws UnparsableExpressionException
+	 *             if the expression could not be translated to RPN
+	 * @throws UnknownFunctionException
+	 *             if an unknown function was encountered
+	 */
+	static String toPostfixExpression(String infixExpression, String[] variableStrings, Set<CustomFunction> customFunctions)
+			throws UnparsableExpressionException, UnknownFunctionException {
+		infixExpression = substituteUnaryOperators(infixExpression);
+		final Token[] tokens = new Tokenizer(variableStrings, customFunctions).tokenize(infixExpression);
+		final StringBuilder output = new StringBuilder(tokens.length);
+		final Stack<Token> operatorStack = new Stack<Token>();
+		for (final Token token : tokens) {
+			token.mutateStackForInfixTranslation(operatorStack, output);
+		}
+		// all tokens read, put the rest of the operations on the output;
+		while (operatorStack.size() > 0) {
+			output.append(operatorStack.pop().getValue()).append(" ");
+		}
+		return output.toString().trim();
+	}
+}

core/src/de/congrace/exp4j/InvalidCustomFunctionException.java

@@ -0,0 +1,9 @@
+package de.congrace.exp4j;
+
+public class InvalidCustomFunctionException extends Exception{
+	private static final long serialVersionUID = 1L;
+
+	public InvalidCustomFunctionException(String message) {
+		super(message);
+	}
+}

core/src/de/congrace/exp4j/NumberToken.java

@@ -0,0 +1,66 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.util.Map;
+import java.util.Stack;
+
+/**
+ * A {@link Token} for Numbers
+ * 
+ * @author fas@congrace.de
+ * 
+ */
+class NumberToken extends CalculationToken {
+
+	private final double doubleValue;
+
+	/**
+	 * construct a new {@link NumberToken}
+	 * 
+	 * @param value
+	 *            the value of the number as a {@link String}
+	 */
+	NumberToken(String value) {
+		super(value);
+		this.doubleValue = Double.parseDouble(value);
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (obj instanceof NumberToken) {
+			final NumberToken t = (NumberToken) obj;
+			return t.getValue().equals(this.getValue());
+		}
+		return false;
+	}
+
+	@Override
+	public int hashCode() {
+		return getValue().hashCode();
+	}
+
+	@Override
+	void mutateStackForCalculation(Stack<Variable> stack, VariableSet variables) {
+		stack.push(new Variable("From number "+getValue()+" : "+hashCode(), this.doubleValue));
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		output.append(this.getValue()).append(' ');
+	}
+}

core/src/de/congrace/exp4j/OperatorToken.java

@@ -0,0 +1,243 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.util.Stack;
+
+/**
+ * {@link Token} for Operations like +,-,*,/,% and ^
+ * 
+ * @author fas@congrace.de
+ */
+class OperatorToken extends CalculationToken {
+
+	/**
+	 * the valid {@link Operation}s for the {@link OperatorToken}
+	 * 
+	 * @author fas@congrace.de
+	 */
+	enum Operation {
+		ADDITION(1, true), SUBTRACTION(1, true), MULTIPLICATION(2, true), DIVISION(2, true), MODULO(2, true), EXPONENTIATION(3, false), UNARY_MINUS(4, false), UNARY_PLUS(
+				4, false);
+		private final int precedence;
+		private final boolean leftAssociative;
+
+		private Operation(int precedence, boolean leftAssociative) {
+			this.precedence = precedence;
+			this.leftAssociative = leftAssociative;
+		}
+	}
+
+	/**
+	 * return a corresponding {@link Operation} for a symbol
+	 * 
+	 * @param c
+	 *            the symbol of the operation
+	 * @return the corresponding {@link Operation}
+	 */
+	static Operation getOperation(char c) {
+		switch (c) {
+		case '+':
+			return Operation.ADDITION;
+		case '-':
+			return Operation.SUBTRACTION;
+		case '*':
+			return Operation.MULTIPLICATION;
+		case '/':
+			return Operation.DIVISION;
+		case '^':
+			return Operation.EXPONENTIATION;
+		case '#':
+			return Operation.UNARY_MINUS;
+		case '%':
+			return Operation.MODULO;
+		default:
+			return null;
+		}
+	}
+
+	static boolean isOperator(char c) {
+		return getOperation(c) != null;
+	}
+
+	private final Operation operation;
+
+	/**
+	 * construct a new {@link OperatorToken}
+	 * 
+	 * @param value
+	 *            the symbol (e.g.: '+')
+	 * @param operation
+	 *            the {@link Operation} of this {@link Token}
+	 */
+	OperatorToken(String value, Operation operation) {
+		super(value);
+		this.operation = operation;
+	}
+	
+	/**
+	 * apply the {@link Operation}
+	 * 
+	 * @param values
+	 *            the doubles to operate on
+	 * @return the result of the {@link Operation}
+	 * @throws UnparsableExpressionException 
+	 */
+	public Variable applyOperation(Variable... values) {
+		
+		values = expandVariables(values);
+		
+		double[] inputs = new double[values.length];
+		switch (values[0].getPrimary()){
+			
+			case DOUBLE:
+				for (int i = 0; i<values.length; i++){
+					inputs[i] = values[i].getDoubleValue();
+				}
+				double result = applyOperation(inputs);
+				return new Variable("double " + operation.name()+" result, ", result);
+			
+			case ARRAY:
+				int maxLength = values[0].getArrayValue().length;
+				double[] results = new double[maxLength];
+				for (int i = 0; i< maxLength; i++){
+					// assemble the array of input values
+					for (int j = 0; j<values.length; j++){
+						inputs[j] = values[j].getArrayValue()[i];
+					}
+					results[i] = applyOperation(inputs);
+				}
+				//System.out.println("Done applying operation "+operation.name());
+				return new Variable("array " + operation.name()+" result, ", results);
+				
+			default:
+				return new Variable("Invalid");
+		}
+	}
+	
+	private double applyOperation(double[] values){
+				
+		//System.out.println("Applying "+operation.toString()+" to values starting "+values[0]);
+		
+		switch (operation) {
+		case ADDITION:
+			return values[0] + values[1];
+		case SUBTRACTION:
+			return values[0] - values[1];
+		case MULTIPLICATION:
+			return values[0] * values[1];
+		case EXPONENTIATION:
+			return Math.pow(values[0], values[1]);
+		case DIVISION:
+			return values[0] / values[1];
+		case UNARY_MINUS:
+			return -values[0];
+		case UNARY_PLUS:
+			return values[0];
+		case MODULO:
+			return values[0] % values[1];
+		default:
+			return 0;
+		}
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (obj instanceof OperatorToken) {
+			final OperatorToken t = (OperatorToken) obj;
+			return t.getValue().equals(this.getValue());
+		}
+		return false;
+	}
+
+	int getOperandCount() {
+		switch (operation) {
+		case ADDITION:
+		case SUBTRACTION:
+		case MULTIPLICATION:
+		case DIVISION:
+		case EXPONENTIATION:
+		case MODULO:
+			return 2;
+		case UNARY_MINUS:
+		case UNARY_PLUS:
+			return 1;
+		default:
+			return 0;
+		}
+	}
+
+	/**
+	 * get the {@link Operation} of this {@link Token}
+	 * 
+	 * @return the {@link Operation}
+	 */
+	Operation getOperation() {
+		return operation;
+	}
+
+	int getPrecedence() {
+		return operation.precedence;
+	}
+
+	@Override
+	public int hashCode() {
+		return getValue().hashCode();
+	}
+
+	/**
+	 * check if the operation is left associative
+	 * 
+	 * @return true if left associative, otherwise false
+	 */
+	boolean isLeftAssociative() {
+		return operation.leftAssociative;
+	}
+
+	@Override
+	void mutateStackForCalculation(Stack<Variable> stack, VariableSet variables) {
+		if (this.getOperandCount() == 2) {
+			final Variable n2 = stack.pop();
+			final Variable n1 = stack.pop();
+			stack.push(this.applyOperation(n1, n2));
+		} else if (this.getOperandCount() == 1) {
+			final Variable n1 = stack.pop();
+			stack.push(this.applyOperation(n1));
+		}
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		Token before;
+		while (!operatorStack.isEmpty() && (before = operatorStack.peek()) != null && (before instanceof OperatorToken || before instanceof FunctionToken)) {
+			if (before instanceof FunctionToken) {
+				operatorStack.pop();
+				output.append(before.getValue()).append(" ");
+			} else {
+				final OperatorToken stackOperator = (OperatorToken) before;
+				if (this.isLeftAssociative() && this.getPrecedence() <= stackOperator.getPrecedence()) {
+					output.append(operatorStack.pop().getValue()).append(" ");
+				} else if (!this.isLeftAssociative() && this.getPrecedence() < stackOperator.getPrecedence()) {
+					output.append(operatorStack.pop().getValue()).append(" ");
+				} else {
+					break;
+				}
+			}
+		}
+		operatorStack.push(this);
+	}
+}

core/src/de/congrace/exp4j/ParenthesisToken.java

@@ -0,0 +1,69 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.util.Stack;
+
+/**
+ * Token for parenthesis
+ * 
+ * @author fas@congrace.de
+ */
+class ParenthesisToken extends Token {
+
+	ParenthesisToken(String value) {
+		super(value);
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (obj instanceof ParenthesisToken) {
+			final ParenthesisToken t = (ParenthesisToken) obj;
+			return t.getValue().equals(this.getValue());
+		}
+		return false;
+	}
+
+	@Override
+	public int hashCode() {
+		return getValue().hashCode();
+	}
+
+	/**
+	 * check the direction of the parenthesis
+	 * 
+	 * @return true if it's a left parenthesis (open) false if it is a right
+	 *         parenthesis (closed)
+	 */
+	boolean isOpen() {
+		return getValue().equals("(") || getValue().equals("[") || getValue().equals("{");
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		if (this.isOpen()) {
+			operatorStack.push(this);
+		} else {
+			Token next;
+			while ((next = operatorStack.peek()) instanceof OperatorToken || next instanceof FunctionToken || next instanceof CustomFunction
+					|| (next instanceof ParenthesisToken && !((ParenthesisToken) next).isOpen())) {
+				output.append(operatorStack.pop().getValue()).append(" ");
+			}
+			operatorStack.pop();
+		}
+	}
+}

core/src/de/congrace/exp4j/PostfixExpression.java

@@ -0,0 +1,116 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.util.Set;
+import java.util.Stack;
+
+/**
+ * Class for calculating values from a RPN postfix expression.<br/>
+ * The default way to create a new instance of {@link PostfixExpression} is by
+ * using the static factory method fromInfix()
+ * 
+ * @author fas@congrace.de
+ */
+public final class PostfixExpression extends AbstractExpression implements Calculable {
+	
+	private VariableSet variables = new VariableSet();
+	
+	/**
+	 * Factory method for creating {@link PostfixExpression}s from human
+	 * readable infix expressions
+	 * 
+	 * @param expression
+	 *            the infix expression to be used
+	 * @return an equivalent {@link PostfixExpression}
+	 * @throws UnparsableExpressionException
+	 *             if the expression was invalid
+	 * @throws UnknownFunctionException
+	 *             if an unknown function has been used
+	 * @deprecated please use {@link ExpressionBuilder} API
+	 */
+    @Deprecated
+	public static PostfixExpression fromInfix(String expression) throws UnparsableExpressionException, UnknownFunctionException {
+		return fromInfix(expression, null);
+	}
+
+	/**
+	 * Factory method for creating {@link PostfixExpression}s from human
+	 * readable infix expressions
+	 * 
+	 * @param expression
+	 *            the infix expression to be used
+	 * @param customFunctions
+	 *            the CustomFunction implementations used
+	 * @return an equivalent {@link PostfixExpression}
+	 * @throws UnparsableExpressionException
+	 *             if the expression was invalid
+	 * @throws UnknownFunctionException
+	 *             if an unknown function has been used
+	 * @deprecated please use {@link ExpressionBuilder}
+	 */
+    @Deprecated
+	public static PostfixExpression fromInfix(String expression, Set<CustomFunction> customFunctions) throws UnparsableExpressionException,
+			UnknownFunctionException {
+		String[] variableStrings = null;
+		int posStart, posEnd;
+		if ((posStart = expression.indexOf('=')) > 0) {
+			String functionDef = expression.substring(0, posStart);
+			expression = expression.substring(posStart + 1);
+			if ((posStart = functionDef.indexOf('(')) > 0 && (posEnd = functionDef.indexOf(')')) > 0) {
+				variableStrings = functionDef.substring(posStart + 1, posEnd).split(",");
+			}
+		}
+		return new PostfixExpression(InfixTranslator.toPostfixExpression(expression, variableStrings, customFunctions), variableStrings, customFunctions);
+	}
+	
+	/**
+	 * Construct a new simple {@link PostfixExpression}
+	 * 
+	 * @param expression
+	 *            the postfix expression to be calculated
+	 * @param variableNames
+	 *            the variable names in the expression
+	 * @param customFunctions
+	 *            the CustomFunction implementations used
+	 * @throws UnparsableExpressionException
+	 *             when expression is invalid
+	 * @throws UnknownFunctionException
+	 *             when an unknown function has been used
+	 */
+	private PostfixExpression(String expression, String[] variableStrings, Set<CustomFunction> customFunctions) throws UnparsableExpressionException,
+			UnknownFunctionException {
+		super(expression, new Tokenizer(variableStrings, customFunctions).tokenize(expression), variableStrings);
+	}
+
+	/**
+	 * delegate the calculation of a simple expression 
+	 */
+	public Variable calculate() throws IllegalArgumentException {
+
+		final Stack<Variable> stack = new Stack<Variable>();
+		for (final Token t : getTokens()) {
+			((CalculationToken) t).mutateStackForCalculation(stack, variables);
+		}
+		return stack.pop();
+
+	}
+
+	public void setVariable(Variable value) {
+		variables.add(value);
+	}
+}

core/src/de/congrace/exp4j/Token.java

@@ -0,0 +1,50 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.util.Stack;
+
+/**
+ * Superclass for tokenized Strings
+ * 
+ * @author fas@congrace.de
+ */
+abstract class Token {
+	private final String value;
+
+	/**
+	 * construct a new {@link Token}
+	 * 
+	 * @param value
+	 *            the value of the {@link Token}
+	 */
+	Token(String value) {
+		super();
+		this.value = value;
+	}
+
+	/**
+	 * get the value (String representation) of the token
+	 * 
+	 * @return the value
+	 */
+	String getValue() {
+		return value;
+	}
+
+	abstract void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output);
+}

core/src/de/congrace/exp4j/Tokenizer.java

@@ -0,0 +1,222 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import de.congrace.exp4j.FunctionToken.Function;
+
+/**
+ * Class for tokenizing mathematical expressions by breaking an expression up
+ * into multiple different {@link Token}s
+ * 
+ * @author fas@congrace.de
+ */
+class Tokenizer {
+	private String[] variableNames;
+	private final Set<String> functionNames = new HashSet<String>();
+	private final Set<CustomFunction> customFunctions;
+
+	{
+		functionNames.add("abs");
+		functionNames.add("acos");
+		functionNames.add("asin");
+		functionNames.add("atan");
+		functionNames.add("cbrt");
+		functionNames.add("ceil");
+		functionNames.add("cos");
+		functionNames.add("cosh");
+		functionNames.add("exp");
+		functionNames.add("expm1");
+		functionNames.add("floor");
+		functionNames.add("log");
+		functionNames.add("sin");
+		functionNames.add("sinh");
+		functionNames.add("sqrt");
+		functionNames.add("tan");
+		functionNames.add("tanh");
+	}
+
+	Tokenizer() {
+		super();
+		customFunctions = null;
+	}
+
+	/**
+	 * construct a new Tokenizer that recognizes variable names
+	 * 
+	 * @param variableNames
+	 *            the variable names in the expression
+	 * @throws IllegalArgumentException
+	 *             if a variable has the name as a function
+	 * @param customFunctions
+	 *            the CustomFunction implementations used if the variableNames
+	 *            are not valid
+	 */
+	Tokenizer(String[] variableNames, Set<CustomFunction> customFunctions) throws IllegalArgumentException {
+		super();		
+		this.variableNames = variableNames;
+				
+		if (variableNames != null) {
+			for (String varName : variableNames) {
+				if (functionNames.contains(varName.toLowerCase())) {
+					throw new IllegalArgumentException("Variable '" + varName + "' can not have the same name as a function");
+				}
+			}
+		}
+		this.customFunctions = customFunctions;
+	}
+
+	private Token getCustomFunctionToken(String name) throws UnknownFunctionException {
+		for (CustomFunction func : customFunctions) {
+			if (func.getValue().equals(name)) {
+				return func;
+			}
+		}
+		throw new UnknownFunctionException(name);
+	}
+
+	private boolean isCustomFunction(String name) {
+		if (customFunctions == null) {
+			return false;
+		}
+		for (CustomFunction func : customFunctions) {
+			if (func.getValue().equals(name)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * check if a char is part of a number
+	 * 
+	 * @param c
+	 *            the char to be checked
+	 * @return true if the char is part of a number
+	 */
+	private boolean isDigit(char c) {
+		return Character.isDigit(c) || c == '.';
+	}
+
+	private boolean isFunction(String name) {
+		for (Function fn : Function.values()) {
+			if (fn.name().equals(name.toUpperCase())) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * check if a String is a variable name
+	 * 
+	 * @param name
+	 *            the variable name which is checked to be valid the char to be
+	 *            checked
+	 * @return true if the char is a variable name (e.g. x)
+	 */
+	private boolean isVariable(String name) {
+		//String[] variableNames = variables.getVariableNames();
+		
+		if (variableNames != null) {
+			for (String var : variableNames) {
+				if (name.equals(var)) {
+					return true;
+				}
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * tokenize an infix expression by breaking it up into different
+	 * {@link Token} that can represent operations,functions,numbers,
+	 * parenthesis or variables
+	 * 
+	 * @param infix
+	 *            the infix expression to be tokenized
+	 * @return the {@link Token}s representing the expression
+	 * @throws UnparsableExpressionException
+	 *             when the expression is invalid
+	 * @throws UnknownFunctionException
+	 *             when an unknown function name has been used.
+	 */
+	Token[] tokenize(String infix) throws UnparsableExpressionException, UnknownFunctionException {
+		final List<Token> tokens = new ArrayList<Token>();
+		final char[] chars = infix.toCharArray();
+		// iterate over the chars and fork on different types of input
+		Token lastToken;
+		for (int i = 0; i < chars.length; i++) {
+			char c = chars[i];
+			if (c == ' ')
+				continue;
+			if (isDigit(c)) {
+				final StringBuilder valueBuilder = new StringBuilder(1);
+				// handle the numbers of the expression
+				valueBuilder.append(c);
+				int numberLen = 1;
+				while (chars.length > i + numberLen && isDigit(chars[i + numberLen])) {
+					valueBuilder.append(chars[i + numberLen]);
+					numberLen++;
+				}
+				i += numberLen - 1;
+				lastToken = new NumberToken(valueBuilder.toString());
+			} else if (Character.isLetter(c) || c == '_' || c == '#') {
+				// can be a variable or function
+				final StringBuilder nameBuilder = new StringBuilder();
+				nameBuilder.append(c);
+				int offset = 1;
+				while (chars.length > i + offset && (Character.isLetter(chars[i + offset]) || Character.isDigit(chars[i + offset]) || chars[i + offset] == '_' || chars[i + offset] == '#')) {
+					nameBuilder.append(chars[i + offset++]);
+				}
+				String name = nameBuilder.toString();
+				if (this.isVariable(name)) {
+					// a variable
+					i += offset - 1;
+					lastToken = new VariableToken(name);
+				} else if (this.isFunction(name)) {
+					// might be a function
+					i += offset - 1;
+					lastToken = new FunctionToken(name);
+				} else if (this.isCustomFunction(name)) {
+					// a custom function
+					i += offset - 1;
+					lastToken = getCustomFunctionToken(name);
+				} else {
+					// an unknown symbol was encountered
+					throw new UnparsableExpressionException(c, i);
+				}
+			}else if (c == ',') {
+			    // a function separator, hopefully
+			    lastToken=new FunctionSeparatorToken();
+			} else if (OperatorToken.isOperator(c)) {
+				lastToken = new OperatorToken(String.valueOf(c), OperatorToken.getOperation(c));
+			} else if (c == '(' || c == ')' || c == '[' || c == ']' || c == '{' || c == '}') {
+				lastToken = new ParenthesisToken(String.valueOf(c));
+			} else {
+				// an unknown symbol was encountered
+				throw new UnparsableExpressionException(c, i);
+			}
+			tokens.add(lastToken);
+		}
+		return tokens.toArray(new Token[tokens.size()]);
+	}
+}

core/src/de/congrace/exp4j/UnknownFunctionException.java

@@ -0,0 +1,37 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+/**
+ * Exception for handling unknown Functions.
+ * 
+ * @see FunctionToken
+ * @author fas@congrace.de
+ */
+public class UnknownFunctionException extends Exception {
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * construct a new {@link UnknownFunctionException}
+	 * 
+	 * @param functionName
+	 *            the function name which could not be found
+	 */
+	public UnknownFunctionException(String functionName) {
+		super("Unknown function: " + functionName);
+	}
+}

core/src/de/congrace/exp4j/UnparsableExpressionException.java

@@ -0,0 +1,47 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+/**
+ * Exception for invalid expressions
+ * 
+ * @author fas@congrace.de
+ */
+public class UnparsableExpressionException extends Exception {
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * construct a new {@link UnparsableExpressionException}
+	 * 
+	 * @param c
+	 *            the character which could not be parsed
+	 * @param pos
+	 *            the position of the character in the expression
+	 */
+	public UnparsableExpressionException(char c, int pos) {
+		super("Unable to parse character at position " + pos + ": '" + String.valueOf(c) + "'");
+	}
+	/**
+	 * construct a new {@link UnparsableExpressionException}
+	 * 
+	 * @param msg 
+	 *            the error message
+	 */
+	public UnparsableExpressionException(String msg) {
+		super(msg);
+	}
+}

core/src/de/congrace/exp4j/Variable.java

@@ -0,0 +1,107 @@
+package de.congrace.exp4j;
+
+/*
+ * Represents a generic variable which can have double or array values.
+ * Optionally the start and step values corresponding to each array index can be specified for array values
+ * Tries to do something sensible if you try and apply a regular function / operator to an array
+ * and vice-versa.
+ */
+public class Variable {
+	
+	// The primary or preferred representation 
+	public enum Primary {DOUBLE, ARRAY, PLACEHOLDER};
+	private final Primary primary;
+	
+	private final String name;
+	
+	private final double doubleValue;  
+	private final double[] arrayValue; 
+	
+	private final double start, step;
+	
+	/*
+	 * Initialize a new variable with a name only. This can be used as a place holder
+	 */
+	public Variable(String name){
+		this.name = name;
+		this.primary = Primary.PLACEHOLDER;
+		this.doubleValue = Double.NaN;
+		this.arrayValue = new double[] {Double.NaN};
+		this.start = Double.NaN;
+		this.step = Double.NaN;
+	}
+	
+	/*
+	 * Initialize a new double variable
+	 */
+	public Variable(String name, double d){
+		this.doubleValue = d;
+		this.arrayValue = new double[] {d};
+		this.name = name;
+		this.primary = Primary.DOUBLE;
+		this.start = Double.NaN;
+		this.step = Double.NaN;
+	}
+	
+	/*
+	 * Initialize a new array variable
+	 */
+	public Variable(String name, double[] d){
+		this.arrayValue = d;
+		this.doubleValue = d[0];
+		this.name = name;
+		this.primary = Primary.ARRAY;
+		this.start = Double.NaN;
+		this.step = Double.NaN;
+	}
+	
+	/*
+	 * Initialize a new array variable, specifying the start and step values
+	 */
+	public Variable(String name, double[] d, double start, double step){
+		this.arrayValue = d;
+		this.doubleValue = d[0];
+		this.name = name;
+		this.primary = Primary.ARRAY;
+		this.start = start;
+		this.step = step;
+	}
+	
+	public String getName(){
+		return name;
+	}
+	
+	public Primary getPrimary(){
+		return this.primary;
+	}
+	
+	public double getDoubleValue(){
+		return doubleValue;
+	}
+	
+	public double[] getArrayValue(){
+		return arrayValue;
+	}
+	
+	public double getStep(){
+		return step;
+	}
+	
+	public double getStart(){
+		return start;
+	}
+	
+	public String toString(){
+		if ( arrayValue.length > 1 ){
+			String out = name + " is Array (length " + new Integer(arrayValue.length).toString() + ") : {";
+			for (double x : arrayValue){
+				out = out + x + ",";
+			}
+			out = out.substring(0, out.length()-1);
+			return out + "}";
+		}
+		else{
+			return name + " is double : {" + new Double(doubleValue).toString() + "}";
+		}
+	}
+}

core/src/de/congrace/exp4j/VariableSet.java

@@ -0,0 +1,42 @@
+package de.congrace.exp4j;
+
+import java.util.HashSet;
+
+public class VariableSet extends HashSet<Variable> {
+
+	/**
+	 * 
+	 */
+	private static final long serialVersionUID = -4212803364398351279L;
+
+	public boolean add(Variable v){
+		Variable previous = getVariableNamed(v.getName());
+		if ( previous != null ){
+			this.remove( previous );
+		}
+			
+		return super.add(v);
+	}
+	
+	public Variable getVariableNamed(String name){
+		for (Variable var : this){
+			if (var.getName().equals(name) ){
+				return var;
+			}
+		}
+		return null;
+	}
+	
+	public String[] getVariableNames(){
+		if (this.size() == 0){
+			return null;
+		}
+		String names[] = new String[this.size()];
+		int i = 0;
+		for (Variable var : this){
+			names[i] = var.getName();
+			i++;
+		}
+		return names;
+	}	
+}

core/src/de/congrace/exp4j/VariableToken.java

@@ -0,0 +1,47 @@
+/*
+   Copyright 2011 frank asseg
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+package de.congrace.exp4j;
+
+import java.util.Stack;
+
+/**
+ * A {@link Token} for representing variables
+ * 
+ * @author fas
+ */
+class VariableToken extends CalculationToken {
+	/**
+	 * construct a new {@link VariableToken}
+	 * 
+	 * @param value
+	 *            the value of the token
+	 */
+	VariableToken(String value) {
+		super(value);
+	}
+
+	@Override
+	void mutateStackForCalculation(Stack<Variable> stack, VariableSet variableValues) {
+		Variable value = variableValues.getVariableNamed(this.getValue());
+		stack.push(value);
+	}
+
+	@Override
+	void mutateStackForInfixTranslation(Stack<Token> operatorStack, StringBuilder output) {
+		output.append(this.getValue()).append(" ");
+	}
+}