Added the MPExpressionTree Classes

MathPad/MPExpressionTree.h

@@ -0,0 +1,28 @@
+//
+//  MPExpressionTree.h
+//  MathPad
+//
+//  Created by Kim Wittenburg on 09.10.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+#import "MPSummand.h"
+#import "MPExpressionTreeElement.h"
+
+@interface MPExpressionTree : NSObject <MPExpressionTreeElement>
+
+@property (nonatomic, copy) NSString *definedVariable;
+
+- (NSArray *)summands;
+- (void)appendSummand:(MPSummand *)summand;
+- (void)insertSummand:(MPSummand *)summand
+              atIndex:(NSUInteger)index;
+- (void)removeSummand:(MPSummand *)summand;
+- (void)removeSummandAtIndex:(NSUInteger)index;
+- (MPSummand *)summandAtIndex:(NSUInteger)index;
+
+- (BOOL)validateExpectingVariableDefinition:(BOOL)flag
+                                      error:(MPParseError *__autoreleasing *)error;
+
+@end