Added Expression Tree Inspection Methods

Cleaned Code

MathPad/MPFunction.m

@@ -7,6 +7,7 @@
 //
 
 #import "MPFunction.h"
+#import "MPExpression.h"
 
 @implementation MPFunction
 
@@ -20,7 +21,13 @@
     return self;
 }
 
-#pragma mark Children
+#pragma mark Working With the Expression Tree
+
+- (void)childChanged:(MPExpression *)child atLocalIndexPath:(NSIndexPath *)indexPath
+{
+    [self.parent functionSymbolChanged:self
+                      atLocalIndexPath:[indexPath indexPathByAddingIndex:0]];
+}
 
 - (NSUInteger)numberOfChildren
 {