diff --git a/MathPad/MPEvaluationContext.h b/MathPad/MPEvaluationContext.h
index 1452d77..f5acfb2 100644
--- a/MathPad/MPEvaluationContext.h
+++ b/MathPad/MPEvaluationContext.h
@@ -15,9 +15,10 @@
 - (void)push;
 - (void)pop;
 
-- (void)bindValue:(NSDecimalNumber *)value toName:(NSString *)variableName;
-- (void)unbindVariableName:(NSString *)variableName;
+- (void)defineVariable:(NSString *)variable withValue:(id)value;
+- (void)undefineVariable:(NSString *)variable;
+- (BOOL)isVariableDefined:(NSString *)variable;
 
-- (NSDecimalNumber *)valueForVariableName:(NSString *)variableName;
+- (NSDecimalNumber *)valueForVariable:(NSString *)variable;
 
 @end
diff --git a/MathPad/MPEvaluationContext.m b/MathPad/MPEvaluationContext.m
index 6e6d0e1..38b9a31 100644
--- a/MathPad/MPEvaluationContext.m
+++ b/MathPad/MPEvaluationContext.m
@@ -45,22 +45,27 @@ static MPEvaluationContext *sharedContext;
     [self.stack removeLastObject];
 }
 
-- (void)bindValue:(NSDecimalNumber *)value toName:(NSString *)variableName
+- (void)defineVariable:(NSString *)variable withValue:(id)value
 {
     NSMutableDictionary *currentBindings = self.stack.lastObject;
-    currentBindings[variableName] = value;
+    currentBindings[variable] = value;
 }
 
-- (void)unbindVariableName:(NSString *)variableName
+- (void)undefineVariable:(NSString *)variable
 {
     NSMutableDictionary *currentBindings = self.stack.lastObject;
-    [currentBindings removeObjectForKey:variableName];
+    [currentBindings removeObjectForKey:variable];
 }
 
-- (NSDecimalNumber *)valueForVariableName:(NSString *)variableName
+- (NSDecimalNumber *)valueForVariable:(NSString *)variable
 {
     NSMutableDictionary *currentBindings = self.stack.lastObject;
-    return currentBindings[variableName];
+    return currentBindings[variable];
+}
+
+- (BOOL)isVariableDefined:(NSString *)variable
+{
+    return [self valueForVariable:variable] != nil;
 }
 
 @end
diff --git a/MathPad/MPExpression.m b/MathPad/MPExpression.m
index 3ab7318..9a8ff35 100644
--- a/MathPad/MPExpression.m
+++ b/MathPad/MPExpression.m
@@ -258,7 +258,9 @@
 
 - (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error
 {
-    return [self.evaluator evaluateWithError:error];
+    MPTerm *term = [self.evaluator parseExpectingVariable:NO
+                                     error:error];
+    return [term evaluate];
 }
 
 @synthesize evaluator = _evaluator;
diff --git a/MathPad/MPExpressionEvaluator.h b/MathPad/MPExpressionEvaluator.h
index f901c1c..185999b 100644
--- a/MathPad/MPExpressionEvaluator.h
+++ b/MathPad/MPExpressionEvaluator.h
@@ -8,7 +8,8 @@
 
 #import <Foundation/Foundation.h>
 #import "MPExpression.h"
-#import "MPElementParser.h"
+#import "MPExpressionTokenizer.h"
+#import "MPTerm.h"
 
 @class MPExpressionEvaluator, MPExpression, MPParsedElementOld;
 
@@ -18,10 +19,14 @@
 - (instancetype)initWithExpression:(MPExpression *)expression;
 @property (readonly, nonatomic, weak) MPExpression *expression;
 
-#pragma mark Evaluating Expressions
-@property (readonly, nonatomic, strong) NSString *definedVariable;
+@property (nonatomic, strong) MPExpressionTokenizer *lexer;
 
-- (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error;
-- (NSDecimalNumber *)evaluateVariableDefinition:(BOOL)flag error:(MPParseError *__autoreleasing *)error;
+- (void)expressionDidChangeInRange:(NSRange)range
+                 replacementLength:(NSUInteger)replacementLength;
+
+#pragma mark Evaluating Expressions
+@property (readonly, nonatomic, copy) NSString *definedVariable;
+
+- (MPTerm *)parseExpectingVariable:(BOOL)flag error:(MPParseError *__autoreleasing *)error;
 
 @end
diff --git a/MathPad/MPExpressionEvaluator.m b/MathPad/MPExpressionEvaluator.m
index 7d07ced..410921e 100644
--- a/MathPad/MPExpressionEvaluator.m
+++ b/MathPad/MPExpressionEvaluator.m
@@ -9,105 +9,236 @@
 #import "MPExpressionEvaluator.h"
 #import "MPExpression.h"
 #import "MPFunction.h"
-#import "MPParsedFactor.h"
-#import "MPFunction+MPParsedFactor.h"
 #import "MPMathRules.h"
+#import "MPToken.h"
+#import "MPFunction+MPToken.h"
+#import "MPTokenStream.h"
+
+#import "MPEvaluationContext.h"
+
+
 
 @interface MPExpressionEvaluator ()
-@property (readwrite, nonatomic, strong) NSString *definedVariable;
+@property (readwrite, nonatomic, copy) NSString *definedVariable;
+@property (nonatomic, strong) NSArray *tokens;
+
+- (void)setError:(MPParseError *)error;
 
 @end
 
 @implementation MPExpressionEvaluator {
-    MPElementParser *parser;
+    MPParseError *__autoreleasing *_error;
+    MPTokenStream *tokenStream;
 }
+
 - (id)initWithExpression:(MPExpression *)expression
 {
     self = [super init];
     if (self) {
         _expression = expression;
-        parser = [[MPElementParser alloc] init];
     }
     return self;
 }
 
-#pragma mark Evaluating Expressions
-- (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error
+@synthesize lexer = _lexer;
+
+- (void)setLexer:(MPExpressionTokenizer *)lexer
 {
-    return [self evaluateVariableDefinition:NO error:error];
+    _lexer = lexer;
+    self.tokens = nil;
 }
 
-- (NSDecimalNumber *)evaluateVariableDefinition:(BOOL)flag error:(MPParseError *__autoreleasing *)error
+- (MPExpressionTokenizer *)lexer
 {
-    // Empty Expression
-    if (self.expression.numberOfElements == 0) {
-        *error = MPParseError(NSMakeRange(0, 0), @"Expected Expression");
+    if (!_lexer) {
+        _lexer = [[MPExpressionTokenizer alloc] init];
+    }
+    return _lexer;
+}
+
+- (NSArray *)tokens
+{
+    if (!_tokens) {
+        _tokens = [self.lexer tokenizeExpression:self.expression];
+    }
+    return _tokens;
+}
+
+- (void)expressionDidChangeInRange:(NSRange)range
+                 replacementLength:(NSUInteger)replacementLength
+{
+    self.tokens = nil;
+}
+
+#pragma mark Evaluating Expressions
+- (void)setError:(MPParseError *)error
+{
+    if (_error) {
+        error.pathToExpression = self.expression.indexPath;
+        *_error = error;
+    }
+}
+
+- (MPTerm *)parseExpectingVariable:(BOOL)flag
+                             error:(MPParseError *__autoreleasing *)error
+{
+    _error = error;
+    tokenStream = [[MPTokenStream alloc] initWithTokens:self.tokens];
+    if (!tokenStream.hasMoreTokens) {
+        self.error = MPParseError(NSMakeRange(0, 0), @"Empty Expression");
         return nil;
     }
-
-    NSMutableArray *products = [[NSMutableArray alloc] init];
-    MPParsedProduct *currentProduct = nil;
     
-    for (NSUInteger elementIndex = 0; elementIndex < self.expression.numberOfElements; elementIndex++) {
+    // Variable Definition
+    if (flag) {
+        MPToken *variableToken = [tokenStream nextToken];
+        MPToken *equalsToken = [tokenStream nextTokenOfType:MPEqualsToken];
         
-        id<MPExpressionElement> element = [self.expression elementAtIndex:elementIndex];
-        
-        if ([element isString]) {
-            id<MPParsedFactor> nextFactor = nil;
-            if (elementIndex < self.expression.numberOfElements - 1) {
-                MPFunction *nextFunction = (MPFunction *)[self.expression elementAtIndex:elementIndex+1];
-                nextFactor = nextFunction;
-            }
-            
-            NSArray *newProducts;
-            if (elementIndex == 0 && flag) {
-                NSString *definedVariable;
-                newProducts = [parser parseElement:(NSString *)element
-                                   previousProduct:currentProduct
-                                        nextFactor:nextFactor
-                                   definesVariable:YES
-                                   definedVariable:&definedVariable
-                                             error:error];
-                self.definedVariable = definedVariable;
-            } else {
-                newProducts = [parser parseElement:(NSString *)element
-                                   previousProduct:currentProduct
-                                        nextFactor:nextFactor
-                                             error:error];
-            }
-            if (!newProducts) {
-                return nil;
-            }
-            
-            for (NSUInteger productIndex = 0; productIndex < newProducts.count-1; productIndex++) {
-                [products addObject:newProducts[productIndex]];
-            }
-            currentProduct = newProducts.lastObject;
-            
-            elementIndex++;
-        } else {
-            if (!currentProduct) {
-                currentProduct = [[MPParsedProduct alloc] init];
-            } else if ([MPMathRules sharedRules].allowsImplicitMultiplication) {
-                [currentProduct addFactor:(MPFunction *)element];
-            } else {
-                *error = MPParseError(NSMakeRange(((MPFunction *)element).range.location, 0), @"Implicit Multiplication not allowed");
-                return nil;
-            }
-        }
-    }
-    
-    [products addObject:currentProduct];
-    
-    NSDecimalNumber *value = [NSDecimalNumber zero];
-    for (MPParsedProduct *product in products) {
-        NSDecimalNumber *productValue = [product evaluateWithError:error];
-        if (!productValue) {
+        if (variableToken.tokenType != MPVariableToken) {
+            self.error = MPParseError(variableToken.range, @"Expected Variable Definition.");
+            return nil;
+        }
+        if (equalsToken.tokenType != MPEqualsToken) {
+            self.error = MPParseError(equalsToken.range, @"Expected \"=\".");
+            return nil;
+        }
+        self.definedVariable = variableToken.stringValue;
+    }
+    
+    BOOL isAtBeginning = YES;
+    NSMutableArray *summands = [[NSMutableArray alloc] init];
+    NSMutableArray *currentSummand = [[NSMutableArray alloc] init];
+    
+    while (tokenStream.hasMoreTokens) {
+        MPToken *multiplicationToken = [tokenStream nextTokenOfType:MPMultiplicationSymbolToken];
+        MPToken *operatorToken = [tokenStream nextTokenOfType:MPOperatorListToken];
+        NSRange valueRange;
+        MPTerm *value = [self nextValue:&valueRange];
+        
+        if (multiplicationToken) {
+            if (isAtBeginning) {
+                self.error = MPParseError(multiplicationToken.range, @"Unexpected Symbol. Expected Number.");
+                return nil;
+            }
+            if (operatorToken) {
+                if (operatorToken.numberOfOperators > [[MPMathRules sharedRules] maximumOperatorChainLengthInMultiplication]) {
+                    self.error = MPParseError(operatorToken.range, @"Too many operators in multiplication");
+                    return nil;
+                }
+                [currentSummand addObject:[[MPTerm alloc] initWithNumber:operatorToken.operatorValue]];
+            }
+            if (value) {
+                [currentSummand addObject:value];
+            } else {
+                return nil;
+            }
+        } else {
+            if (operatorToken) {
+                if (operatorToken.numberOfOperators > [[MPMathRules sharedRules] maximumOperatorChainLength]) {
+                    self.error = MPParseError(operatorToken.range, @"Too many operators.");
+                    return nil;
+                }
+                [summands addObject:[[MPTerm alloc] initWithFactors:currentSummand.copy]];
+                currentSummand = [[NSMutableArray alloc] init];
+                [currentSummand addObject:[[MPTerm alloc] initWithNumber:operatorToken.operatorValue]];
+                if (value) {
+                    [currentSummand addObject:value];
+                } else {
+                    return nil;
+                }
+            } else if (!value) {
+                return nil;
+            } else if (isAtBeginning || [[MPMathRules sharedRules] allowsImplicitMultiplication]) {
+                [currentSummand addObject:value];
+            } else {
+                self.error = MPParseError(NSMakeRange(valueRange.location, 0), @"Implicit Multiplication not allowed here");
+                return nil;
+            }
+        }
+        
+        isAtBeginning = NO;
+    }
+    [summands addObject:[[MPTerm alloc] initWithFactors:currentSummand.copy]];
+    return [[MPTerm alloc] initWithSummands:summands.copy];
+}
+
+- (MPTerm *)nextValue:(NSRangePointer)range
+{
+    MPToken *token = [tokenStream nextToken];
+    if (range) {
+        *range = token.range;
+    }
+    switch (token.tokenType) {
+        case MPNumberToken:
+        {
+            return [[MPTerm alloc] initWithNumber:token.number];
+        }
+            
+        case MPVariableToken:
+        {
+            if(![[MPEvaluationContext sharedContext] isVariableDefined:token.variable]) {
+                self.error = MPParseError(token.range, @"Undefined Variable");
+                return nil;
+            }
+            return [[MPTerm alloc] initWithVariable:token.variable];
+        }
+            
+        case MPGenericFunctionToken:
+        {
+            return [((MPFunction *)token) parseWithError:_error];
+        }
+            
+        case MPSinToken:
+        {
+            NSRange sinTermRange;
+            MPTerm *sinTerm = [self nextValue:&sinTermRange];
+            if (!sinTerm) {
+                if (range) {
+                    *range = NSUnionRange(token.range, sinTermRange);
+                }
+                return nil;
+            }
+            return [[MPTerm alloc] initWithSinOfTerm:sinTerm];
+        }
+            
+        case MPCosToken:
+        {
+            NSRange cosTermRange;
+            MPTerm *cosTerm = [self nextValue:&cosTermRange];
+            if (!cosTerm) {
+                if (range) {
+                    *range = NSUnionRange(token.range, cosTermRange);
+                }
+                return nil;
+            }
+            return [[MPTerm alloc] initWithSinOfTerm:cosTerm];
+        }
+            
+        case MPTanToken:
+        {
+            NSRange tanTermRange;
+            MPTerm *tanTerm = [self nextValue:&tanTermRange];
+            if (!tanTerm) {
+                if (range) {
+                    *range = NSUnionRange(token.range, tanTermRange);
+                }
+                return nil;
+            }
+            return [[MPTerm alloc] initWithTanOfTerm:tanTerm];
+        }
+
+        case MPEOFToken:
+        {
+            self.error = MPParseError(token.range, @"Unexpected End. Expected Number.");
+            return nil;
+        }
+            
+        default:
+        {
+            self.error = MPParseError(token.range, @"Unexpected Symbol. Expected Number.");
             return nil;
         }
-        value = [value decimalNumberByAdding:productValue];
     }
-    return value;
 }
 
 @end
diff --git a/MathPad/MPExpressionTokenizer.h b/MathPad/MPExpressionTokenizer.h
new file mode 100644
index 0000000..8b8b012
--- /dev/null
+++ b/MathPad/MPExpressionTokenizer.h
@@ -0,0 +1,16 @@
+//
+//  MPExpressionLexer.h
+//  MathPad
+//
+//  Created by Kim Wittenburg on 19.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+#import "MPExpression.h"
+
+@interface MPExpressionTokenizer : NSObject
+
+- (NSArray *)tokenizeExpression:(MPExpression *)expression; // Returns MPToken's
+
+@end
diff --git a/MathPad/MPExpressionTokenizer.m b/MathPad/MPExpressionTokenizer.m
new file mode 100644
index 0000000..126f3e0
--- /dev/null
+++ b/MathPad/MPExpressionTokenizer.m
@@ -0,0 +1,115 @@
+//
+//  MPExpressionLexer.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 19.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPExpressionTokenizer.h"
+#import "MPToken.h"
+#import "MPFunction+MPToken.h"
+
+#import "NSRegularExpression+MPParsingAdditions.h"
+
+
+#define MPRangeExists(range) (range.location != NSNotFound)
+
+
+@implementation MPExpressionTokenizer
+
+- (NSArray *)tokenizeExpression:(MPExpression *)expression
+{
+    NSMutableArray *tokens = [[NSMutableArray alloc] init];
+    for (NSUInteger index = 0; index < expression.numberOfElements; index++) {
+        id <MPExpressionElement> element = [expression elementAtIndex:index];
+        if ([element isFunction]) {
+            [tokens addObject:element];
+        } else {
+            [tokens addObjectsFromArray:[self tokenizeElement:(NSString *)element]];
+        }
+    }
+    return tokens;
+}
+
+- (NSArray *)tokenizeElement:(NSString *)element
+{
+    NSUInteger lexLocation = 0;
+    
+    NSString *decimalSeparator = [NSRegularExpression escapedPatternForString:[[NSLocale currentLocale] objectForKey:NSLocaleDecimalSeparator]];
+    NSString *regexStringFormat = @"\\A(?:"
+                            @"(\\*)|"
+                            @"([+-](?:\\s*[+-])*)|"
+                            @"((?:\\d+(?:%@\\d+)?)|(?:\\s%@\\d+))|"
+                            @"(sin)|"
+                            @"(cos)|"
+                            @"(tan)|"
+                            @"([A-Za-z])|"
+                            @"(=)|"
+                            @"(\\s)"
+                            @")";
+    NSString *regexString = [NSString stringWithFormat:regexStringFormat, decimalSeparator, decimalSeparator];
+    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regexString
+                                                                           options:0
+                                                                             error:NULL];
+    NSMutableArray *tokens = [[NSMutableArray alloc] init];
+    while (lexLocation < element.length) {
+        NSTextCheckingResult *match = [regex firstMatchInString:element fromIndex:lexLocation];
+        
+        NSRange range = NSMakeRange(lexLocation, 1);
+        MPTokenType tokenType = MPUnidentifiedToken;
+        if (match) {
+            NSRange multiplicationSymbolRange = [match rangeAtIndex:1];
+            NSRange operatorRange = [match rangeAtIndex:2];
+            NSRange numberRange = [match rangeAtIndex:3];
+            NSRange sinRange = [match rangeAtIndex:4];
+            NSRange cosRange = [match rangeAtIndex:5];
+            NSRange tanRange = [match rangeAtIndex:6];
+            NSRange variableRange = [match rangeAtIndex:7];
+            NSRange equalsRange = [match rangeAtIndex:8];
+            NSRange whitespaceRange = [match rangeAtIndex:9];
+        
+            if (MPRangeExists(multiplicationSymbolRange)) {
+                range = multiplicationSymbolRange;
+                tokenType = MPMultiplicationSymbolToken;
+            } else if (MPRangeExists(operatorRange)) {
+                range = operatorRange;
+                tokenType = MPOperatorListToken;
+            } else if (MPRangeExists(numberRange)) {
+                range = numberRange;
+                tokenType = MPNumberToken;
+            } else if (MPRangeExists(sinRange)) {
+                range = sinRange;
+                tokenType = MPSinToken;
+            } else if (MPRangeExists(cosRange)) {
+                range = cosRange;
+                tokenType = MPCosToken;
+            } else if (MPRangeExists(tanRange)) {
+                range = tanRange;
+                tokenType = MPTanToken;
+            } else if (MPRangeExists(variableRange)) {
+                range = variableRange;
+                tokenType = MPVariableToken;
+            } else if (MPRangeExists(equalsRange)) {
+                range = equalsRange;
+                tokenType = MPEqualsToken;
+            } else if (MPRangeExists(whitespaceRange)) {
+                range = whitespaceRange;
+                tokenType = MPWhitespaceToken;
+            } else {
+                // Should not get here
+                range = NSMakeRange(lexLocation, 1);
+                tokenType = MPUnidentifiedToken;
+            }
+        }
+        
+        lexLocation = NSMaxRange(range);
+        [tokens addObject:[[MPToken alloc] initWithTokenType:tokenType
+                                                       range:range
+                                                    inString:element]];
+    }
+    
+    return tokens;
+}
+
+@end
diff --git a/MathPad/MPFunction+MPToken.h b/MathPad/MPFunction+MPToken.h
new file mode 100644
index 0000000..44e45fc
--- /dev/null
+++ b/MathPad/MPFunction+MPToken.h
@@ -0,0 +1,14 @@
+//
+//  MPFunction+MPToken.h
+//  MathPad
+//
+//  Created by Kim Wittenburg on 19.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import <MathKit/MathKit.h>
+#import "MPToken.h"
+
+@interface MPFunction (MPToken) <MPToken>
+
+@end
diff --git a/MathPad/MPFunction+MPToken.m b/MathPad/MPFunction+MPToken.m
new file mode 100644
index 0000000..94a939a
--- /dev/null
+++ b/MathPad/MPFunction+MPToken.m
@@ -0,0 +1,34 @@
+//
+//  MPFunction+MPToken.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 19.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPFunction+MPToken.h"
+
+@implementation MPFunction (MPToken)
+
+- (MPTokenType)tokenType
+{
+    return MPGenericFunctionToken;
+}
+
+- (NSRange)range
+{
+    NSUInteger selfIndex = [self.parent indexOfElement:self];
+    return NSMakeRange([self.parent locationOfElementAtIndex:selfIndex], 1);
+}
+
+- (BOOL)exists
+{
+    return YES;
+}
+
+- (NSString *)stringValue
+{
+    return [self description];
+}
+
+@end
diff --git a/MathPad/MPFunction.h b/MathPad/MPFunction.h
index 1cbbc2b..eccb0b4 100644
--- a/MathPad/MPFunction.h
+++ b/MathPad/MPFunction.h
@@ -9,11 +9,14 @@
 @import Foundation;
 #import "MPExpressionElement.h"
 #import "MPParseError.h"
+#import "MPTerm.h"
 
 @class MPFunction, MPExpression, MPRangePath;
 
 @interface MPFunction : NSObject <NSCoding, NSCopying, MPExpressionElement>
 
++ (NSString *)localizedFunctionName; // Override
+
 #pragma mark Creation Methods
 
 - (instancetype)init;
@@ -38,7 +41,8 @@
 - (id)elementAtIndexPath:(NSIndexPath *)indexPath;
 
 #pragma mark Evaluating Functions
-- (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error;
+
+- (MPTerm *)parseWithError:(MPParseError *__autoreleasing *)error; // Override
 
 #pragma mark Messages
 - (void)didChangeElementsInRangePath:(MPRangePath *)rangePath
@@ -52,4 +56,6 @@
 - (NSString *)description; // Should be overridden
 - (NSUInteger)hash;// Override
 
+- (id)copyWithZone:(NSZone *)zone; // Override
+
 @end
diff --git a/MathPad/MPFunction.m b/MathPad/MPFunction.m
index 141c56b..7e28658 100644
--- a/MathPad/MPFunction.m
+++ b/MathPad/MPFunction.m
@@ -14,6 +14,11 @@
 
 @implementation MPFunction
 
++ (NSString *)localizedFunctionName
+{
+    return NSLocalizedString(@"Function", @"Name of Generic Function.");
+}
+
 #pragma mark Creation Methods
 - (instancetype)init
 {
@@ -82,9 +87,9 @@
 }
 
 #pragma mark Evaluating Functions
-- (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error
+- (MPTerm *)parseWithError:(MPParseError *__autoreleasing *)error
 {
-    return [NSDecimalNumber zero];
+    return nil;
 }
 
 #pragma mark Notifications
diff --git a/MathPad/MPParseError.h b/MathPad/MPParseError.h
index 4c60175..f01a328 100644
--- a/MathPad/MPParseError.h
+++ b/MathPad/MPParseError.h
@@ -6,8 +6,12 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
+// TODO: Rename to MPSyntaxError
+
 #import <Foundation/Foundation.h>
 
+@class MPRangePath;
+
 #define MPParseError(range,key) [[MPParseError alloc] initWithErrorRange:range errorMessageKey:key]
 
 @interface MPParseError : NSObject
@@ -23,4 +27,6 @@
 @property (nonatomic) NSRange errorRange;
 @property (nonatomic, copy) NSString *localizedErrorMessage;
 
+- (MPRangePath *)rangePath;
+
 @end
diff --git a/MathPad/MPParseError.m b/MathPad/MPParseError.m
index 1ca6f72..c6a9db3 100644
--- a/MathPad/MPParseError.m
+++ b/MathPad/MPParseError.m
@@ -8,6 +8,9 @@
 
 #import "MPParseError.h"
 
+#import "MPRangePath.h"
+#import "NSIndexPath+MPAdditions.h"
+
 @implementation MPParseError
 
 - (instancetype)initWithErrorRange:(NSRange)errorRange errorMessageKey:(NSString *)key
@@ -30,6 +33,14 @@
     return self;
 }
 
+- (MPRangePath *)rangePath
+{
+    NSIndexPath *location = self.pathToExpression;
+    location = [location indexPathByPreceedingIndex:self.errorRange.location];
+    MPRangePath *rangePath = [MPRangePath rangePathWithLocation:location length:self.errorRange.length];
+    return rangePath;
+}
+
 - (NSString *)description
 {
     return [NSString stringWithFormat:@"MPParseError<at=(%ld, %ld) message=\"%@\">", self.errorRange.location, self.errorRange.length, self.localizedErrorMessage];
diff --git a/MathPad/MPTerm.h b/MathPad/MPTerm.h
new file mode 100644
index 0000000..6b69acd
--- /dev/null
+++ b/MathPad/MPTerm.h
@@ -0,0 +1,26 @@
+//
+//  MPTerm.h
+//  MathPad
+//
+//  Created by Kim Wittenburg on 27.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+@import Foundation;
+
+@interface MPTerm : NSObject
+
+- (instancetype)initWithBlock:(NSDecimalNumber *(^)())block; // Designated Initializer
+
+- (instancetype)initWithNumber:(NSDecimalNumber *)number;
+- (instancetype)initWithSummands:(NSArray *)summands; // array of MPTerms
+- (instancetype)initWithFactors:(NSArray *)factors; // array of MPTerms
+- (instancetype)initWithVariable:(NSString *)variable;
+
+- (instancetype)initWithSinOfTerm:(MPTerm *)term;
+- (instancetype)initWithCosOfTerm:(MPTerm *)term;
+- (instancetype)initWithTanOfTerm:(MPTerm *)term;
+
+- (NSDecimalNumber *)evaluate;
+
+@end
diff --git a/MathPad/MPTerm.m b/MathPad/MPTerm.m
new file mode 100644
index 0000000..20e9d9e
--- /dev/null
+++ b/MathPad/MPTerm.m
@@ -0,0 +1,94 @@
+//
+//  MPTerm.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 27.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPTerm.h"
+#import "MPEvaluationContext.h"
+
+@interface MPTerm ()
+
+@property (nonatomic, copy) NSDecimalNumber *(^block)();
+
+@end
+
+@implementation MPTerm
+
+- (instancetype)initWithBlock:(NSDecimalNumber *(^)())block
+{
+    self = [super init];
+    if (self) {
+        self.block = block;
+    }
+    return self;
+}
+
+- (instancetype)initWithNumber:(NSDecimalNumber *)number
+{
+    return [self initWithBlock:^NSDecimalNumber *{
+        return number;
+    }];
+}
+
+- (instancetype)initWithSummands:(NSArray *)summands
+{
+    return [self initWithBlock:^NSDecimalNumber *{
+        NSDecimalNumber *value = [NSDecimalNumber zero];
+        for (MPTerm *term in summands) {
+            value = [value decimalNumberByAdding:[term evaluate]];
+        }
+        return value;
+    }];
+}
+
+- (instancetype)initWithFactors:(NSArray *)factors
+{
+    return [self initWithBlock:^NSDecimalNumber *{
+        NSDecimalNumber *value = [NSDecimalNumber one];
+        for (MPTerm *term in factors) {
+            value = [value decimalNumberByMultiplyingBy:[term evaluate]];
+        }
+        return value;
+    }];
+}
+
+- (instancetype)initWithVariable:(NSString *)variable
+{
+    return [self initWithBlock:^NSDecimalNumber *{
+        return [[MPEvaluationContext sharedContext] valueForVariable:variable];
+    }];
+}
+
+- (instancetype)initWithSinOfTerm:(MPTerm *)term
+{
+    return [self initWithBlock:^NSDecimalNumber *{
+        NSDecimalNumber *sinValue = [term evaluate];
+        return [[NSDecimalNumber alloc] initWithDouble:sin(sinValue.doubleValue)];
+    }];
+}
+
+- (instancetype)initWithCosOfTerm:(MPTerm *)term
+{
+    return [self initWithBlock:^NSDecimalNumber *{
+        NSDecimalNumber *cosValue = [term evaluate];
+        return [[NSDecimalNumber alloc] initWithDouble:cos(cosValue.doubleValue)];
+    }];
+}
+
+- (instancetype)initWithTanOfTerm:(MPTerm *)term
+{
+    return [self initWithBlock:^NSDecimalNumber *{
+        NSDecimalNumber *tanValue = [term evaluate];
+        return [[NSDecimalNumber alloc] initWithDouble:tan(tanValue.doubleValue)];
+    }];
+}
+
+- (NSDecimalNumber *)evaluate
+{
+    return self.block();
+}
+
+@end
diff --git a/MathPad/MPToken.h b/MathPad/MPToken.h
new file mode 100644
index 0000000..fbeb113
--- /dev/null
+++ b/MathPad/MPToken.h
@@ -0,0 +1,60 @@
+//
+//  MPToken.h
+//  MathPad
+//
+//  Created by Kim Wittenburg on 19.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+typedef NS_ENUM(NSUInteger, MPTokenType) {
+    MPEOFToken = 0,
+    MPMultiplicationSymbolToken,
+    MPOperatorListToken,
+    MPSinToken,
+    MPCosToken,
+    MPTanToken,
+    MPNumberToken,
+    MPVariableToken,
+    MPEqualsToken,
+    MPGenericFunctionToken,
+    
+    MPWhitespaceToken,
+    MPUnidentifiedToken,
+    
+    MPCompoundToken
+};
+
+
+@protocol MPToken <NSObject>
+
+- (MPTokenType)tokenType;
+
+- (NSRange)range;
+- (NSString *)stringValue;
+
+@end
+
+
+@interface MPToken : NSObject <MPToken>
+
+- (instancetype)initEOFTokenAtLocation:(NSUInteger)eofLocation;
+- (instancetype)initWithRange:(NSRange)range inString:(NSString *)input;
+- (instancetype)initWithTokenType:(MPTokenType)tokenType
+                            range:(NSRange)range
+                     inString:(NSString *)input;
+
+@end
+
+@interface MPToken (MPTokenExtension)
+// Methods are only available for respective token type
+
+- (NSUInteger)numberOfOperators;
+- (NSDecimalNumber *)operatorValue;
+
+- (NSDecimalNumber *)number;
+
+- (NSString *)variable;
+
+@end
\ No newline at end of file
diff --git a/MathPad/MPToken.m b/MathPad/MPToken.m
new file mode 100644
index 0000000..512684f
--- /dev/null
+++ b/MathPad/MPToken.m
@@ -0,0 +1,104 @@
+//
+//  MPToken.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 19.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPToken.h"
+
+@implementation MPToken {
+    NSRange _range;
+    MPTokenType _tokenType;
+    NSString *_stringValue;
+}
+
+- (instancetype)initEOFTokenAtLocation:(NSUInteger)eofLocation
+{
+    self = [super init];
+    if (self) {
+        _range = NSMakeRange(eofLocation, 0);
+    }
+    return self;
+}
+
+- (instancetype)initWithRange:(NSRange)range inString:(NSString *)input
+{
+    self = [super init];
+    if (self) {
+        _range = range;
+        _stringValue = [input substringWithRange:range].copy;
+    }
+    return self;
+}
+
+- (instancetype)initWithTokenType:(MPTokenType)tokenType
+                            range:(NSRange)range
+                         inString:(NSString *)input
+{
+    self = [self initWithRange:range
+                      inString:input];
+    if (self) {
+        _tokenType = tokenType;
+    }
+    return self;
+}
+
+- (NSRange)range
+{
+    return _range;
+}
+
+- (MPTokenType)tokenType
+{
+    return _tokenType;
+}
+
+- (NSString *)stringValue
+{
+    return _stringValue;
+}
+
+- (NSString *)description
+{
+    return self.stringValue;
+}
+
+@end
+
+
+@implementation MPToken (MPTokenExtension)
+
+- (NSUInteger)numberOfOperators
+{
+    NSString *operatorString = [[self.stringValue componentsSeparatedByString:@" "] componentsJoinedByString:@""];
+    return operatorString.length;
+}
+
+- (NSDecimalNumber *)operatorValue
+{
+    NSString *operatorString = [[self.stringValue componentsSeparatedByString:@" "] componentsJoinedByString:@""];
+    NSDecimalNumber *value = [NSDecimalNumber one];
+    for (NSUInteger charIndex = 0; charIndex < operatorString.length; charIndex++) {
+        NSString *operator = [operatorString substringWithRange:NSMakeRange(charIndex, 1)];
+        if ([operator isEqualToString:@"-"]) {
+            value = [value decimalNumberByMultiplyingBy:[[NSDecimalNumber alloc] initWithInteger:-1]];
+        }
+    }
+    return value;
+}
+
+- (NSDecimalNumber *)number
+{
+    return [NSDecimalNumber decimalNumberWithString:self.stringValue
+                                             locale:[NSLocale currentLocale]];
+}
+
+- (NSString *)variable
+{
+    return self.stringValue;
+}
+
+
+@end
diff --git a/MathPad/MPTokenStream.h b/MathPad/MPTokenStream.h
new file mode 100644
index 0000000..05fc9f6
--- /dev/null
+++ b/MathPad/MPTokenStream.h
@@ -0,0 +1,27 @@
+//
+//  MPTokenStream.h
+//  MathPad
+//
+//  Created by Kim Wittenburg on 20.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+#import "MPToken.h"
+
+@interface MPTokenStream : NSObject
+
+- (instancetype)initWithTokens:(NSArray *)tokens;
+
+@property (nonatomic, copy) NSArray *tokens;
+@property (nonatomic, getter=isIgnoringWhitespaceTokens) BOOL ignoringWhitespaceTokens; // Default: YES
+
+@property (readonly, nonatomic) NSUInteger currentLocation;
+
+- (void)reset;
+- (BOOL)hasMoreTokens;
+
+- (MPToken *)nextToken;
+- (MPToken *)nextTokenOfType:(MPTokenType)type;
+
+@end
diff --git a/MathPad/MPTokenStream.m b/MathPad/MPTokenStream.m
new file mode 100644
index 0000000..37f0ebe
--- /dev/null
+++ b/MathPad/MPTokenStream.m
@@ -0,0 +1,90 @@
+//
+//  MPTokenStream.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 20.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPTokenStream.h"
+
+@interface MPTokenStream ()
+@property (readwrite, nonatomic) NSUInteger currentLocation;
+@end
+
+@implementation MPTokenStream {
+    NSUInteger currentTokenIndex;
+    NSUInteger eofLocation;
+}
+
+- (instancetype)initWithTokens:(NSArray *)tokens
+{
+    self = [super init];
+    if (self) {
+        self.tokens = tokens;
+        self.ignoringWhitespaceTokens  = YES;
+        if (tokens.count > 0) {
+            eofLocation = NSMaxRange([tokens.lastObject range]);
+        }
+        [self reset];
+    }
+    return self;
+}
+
+- (void)skipWhitespaces
+{
+    if (!self.isIgnoringWhitespaceTokens) {
+        return;
+    }
+    while (currentTokenIndex < self.tokens.count) {
+        MPToken *token = self.tokens[currentTokenIndex];
+        if (token.tokenType != MPWhitespaceToken) {
+            return;
+        }
+        self.currentLocation = NSMaxRange(token.range);
+        ++currentTokenIndex;
+    }
+}
+
+- (void)reset
+{
+    currentTokenIndex = 0;
+    self.currentLocation = 0;
+    [self skipWhitespaces];
+}
+
+- (BOOL)hasMoreTokens
+{
+    [self skipWhitespaces];
+    return currentTokenIndex < self.tokens.count;
+}
+
+- (MPToken *)nextToken
+{
+    [self skipWhitespaces];
+    if (currentTokenIndex >= self.tokens.count) {
+        return [[MPToken alloc] initEOFTokenAtLocation:eofLocation];
+    } else {
+        MPToken *token = self.tokens[currentTokenIndex++];
+        self.currentLocation = NSMaxRange(token.range);
+        return token;
+    }
+}
+
+- (MPToken *)nextTokenOfType:(MPTokenType)type
+{
+    [self skipWhitespaces];
+    if (currentTokenIndex >= self.tokens.count) {
+        return nil;
+    } else {
+        MPToken *token = self.tokens[currentTokenIndex];
+        if (token.tokenType != type) {
+            return nil;
+        }
+        ++currentTokenIndex;
+        self.currentLocation = NSMaxRange(token.range);
+        return token;
+    }
+}
+
+@end