Added some methods to „Working With the Expression Tree“ section

MathPad/MPFunction.m

@@ -9,6 +9,8 @@
 #import "MPFunction.h"
 #import "MPExpression.h"
 
+#import "NSIndexPath+MPRemoveFirstIndex.h"
+
 @implementation MPFunction
 
 #pragma mark Creation Methods
@@ -90,7 +92,7 @@
 
 @implementation MPFunction (MPFunctionExtensionMethods)
 
-#pragma mark Children
+#pragma mark Working With the Expression Tree
 
 - (NSArray *)children
 {
@@ -102,6 +104,26 @@
     return [children copy];
 }
 
+- (NSUInteger)indexOfChild:(MPExpression *)child
+{
+    NSUInteger index = 0;
+    for (; index < [self numberOfChildren]; index++) {
+        if ([[self childAtIndex:index] isEqualToExpression:child]) {
+            return index;
+        }
+    }
+    return NSNotFound;
+}
+
+- (id)symbolAtIndexPath:(NSIndexPath *)indexPath
+{
+    if (indexPath.length == 0) {
+        return self;
+    }
+    MPExpression *child = [self childAtIndex:[indexPath indexAtPosition:0]];
+    return [child symbolAtIndexPath:[indexPath indexPathByRemovingFirstIndex]];
+}
+
 #pragma mark Evaluating Functions
 
 - (float)floatValue