Added the MPExpressionTree Classes

MathPad/MPFunctionValue.h

@@ -0,0 +1,19 @@
+//
+//  MPFunctionValue.h
+//  MathPad
+//
+//  Created by Kim Wittenburg on 11.10.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import <Cocoa/Cocoa.h>
+#import "MPValueGroup.h"
+
+@interface MPFunctionValue : NSObject <MPValue>
+
+- (instancetype)initWithTokenStream:(MPTokenStream *)tokenStream; // May return an MPFunctionValue or a powered function
+
+@property (nonatomic, copy) NSString *functionName;
+@property (nonatomic, strong) MPValueGroup *valueGroup;
+
+@end