Started to Implement Evaluation

Corrected Some Errors
Cleaned Code

MathPad/MPLayout.m

@@ -128,6 +128,16 @@
 }
 
 #pragma mark Calculation and Drawing Methods
+- (CTLineRef)createLineForString:(NSString *)aString
+{
+    NSAttributedString *text = [[NSAttributedString alloc] initWithString:aString
+                                                               attributes:@{NSFontAttributeName: self.font}];
+    CFAttributedStringRef attributedString = CFBridgingRetain(text);
+    CTLineRef line = CTLineCreateWithAttributedString(attributedString);
+    CFRelease(attributedString); // TODO: Is this release appropriate?
+    return line;
+}
+
 - (NSRect)bounds
 {
     if (NSEqualRects(_cachedBounds, NSZeroRect)) {
@@ -161,33 +171,4 @@
     [transform concat];
 }
 
-@end
-
-@implementation MPLayout (MPSubclassImplement)
-
-- (MPLayout *)childLayoutAtIndex:(NSUInteger)index
-{
-    return nil;
-}
-
-- (NSRect)generateBounds
-{
-    return NSZeroRect;
-}
-
-- (NSRect)boundingRectForRange:(NSRange)range
-{
-    return NSZeroRect;
-}
-
-- (NSPoint)offsetOfChildLayoutAtIndex:(NSUInteger)index
-{
-    return NSZeroPoint;
-}
-
-- (void)draw
-{
-    
-}
-
-@end
+@end