Internal Redesign:

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

MathPad/NSString+MPExpressionElement.m

@@ -0,0 +1,49 @@
+//
+//  NSString+MPExpressionElement.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 10.08.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "NSString+MPExpressionElement.h"
+
+@implementation NSString (MPExpressionElement)
+
+- (BOOL)isString
+{
+    return YES;
+}
+
+- (BOOL)isFunction
+{
+    return NO;
+}
+
+- (double)doubleValue
+{
+#warning Unimplemented Method
+    return 0;
+}
+
+- (float)floatValue
+{
+    return (float)[self doubleValue];
+}
+
+- (int)intValue
+{
+    return (int)[self doubleValue];
+}
+
+- (NSInteger)integerValue
+{
+    return (NSInteger)[self doubleValue];
+}
+
+- (long long)longLongValue
+{
+    return (long long)[self doubleValue];
+}
+
+@end