Internal Redesign:

- Combined MPExpression and MPMutableExpression
- Abstracted children of MPExpression into MPExpressionElement protocol
- Abstracted most of MPExpressionLayout and MPFunctionLayout into common superclass MPLayout

MathPad/MPFunction.h

@@ -6,58 +6,47 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
+@import Foundation;
+#import "MPExpressionElement.h"
+
 @class MPFunction, MPExpression, MPRangePath;
 
-@interface MPFunction : NSObject <NSCopying, NSCoding>
+@interface MPFunction : NSObject <NSCoding, NSCopying, MPExpressionElement>
 
 #pragma mark Creation Methods
 
 - (instancetype)init;
 
-#pragma mark Working With the Expression Tree
+#pragma mark Properties
+// Subclasses should define accessor properties for all sub expressions, which, in the setter, should send didChangeElementAtRangePath:replacementLength: to self with a replacement length of 1.
 
+#pragma mark Working With the Expression Tree
 @property (nonatomic, weak) MPExpression *parent; // Documentation: Do not set
 
-- (NSUInteger)numberOfChildren;
-- (MPExpression *)childAtIndex:(NSUInteger)index;
+- (NSUInteger)numberOfChildren; // Override
+- (MPExpression *)childAtIndex:(NSUInteger)index; // Override
 - (void)setChild:(MPExpression *)child
-         atIndex:(NSUInteger)index;
-
-#pragma mark Evaluating Functions
-
-- (double)doubleValue;
-
-#pragma mark Working With Functions
-
-- (BOOL)isEqualToFunction:(MPFunction *)aFunction;
-
-@end
-
-@interface MPFunction (MPFunctionExtensionMethods)
-
-#pragma mark Working With the Expression Tree
+         atIndex:(NSUInteger)index; // Override
 
 // May be overridden for performance improvements
-- (NSArray *)children;
+- (NSArray *)children; // Indexes must equal the ones from the native methods
 - (NSUInteger)indexOfChild:(MPExpression *)child;
 
-- (id)symbolAtIndexPath:(NSIndexPath *)indexPath;
+- (id)elementAtIndexPath:(NSIndexPath *)indexPath;
 
 #pragma mark Evaluating Functions
+- (double)doubleValue; // Override
 
-- (float)floatValue;
-- (int)intValue;
-- (NSInteger)integerValue;
-- (long long)longLongValue;
+#pragma mark Messages
+- (void)didChangeElementsInRangePath:(MPRangePath *)rangePath
+                   replacementLength:(NSUInteger)replacementLength;
+- (void)didChangeChild:(MPExpression *)child;
+- (void)didChangeChildAtIndex:(NSUInteger)index;
 
-- (NSString *)description;
+#pragma mark Working With Functions
+- (BOOL)isEqualToFunction:(MPFunction *)aFunction; // Override
 
-- (NSUInteger)hash;
-
-@end
-
-@interface MPFunction (MPDisplayExtension)
-
-- (void)symbolsChangedInRangePath:(MPRangePath *)rangePath replacementLength:(NSUInteger)length;
+- (NSString *)description; // Should be overridden
+- (NSUInteger)hash;// Override
 
 @end