Added Function Chooser as a Popover

Improved Evaluation
Added Parenthesis Function

MathPad/MPParenthesisFunction.m

@@ -0,0 +1,90 @@
+
+//
+//  MPParenthesisFunction.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 17.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPParenthesisFunction.h"
+#import "MPExpressionEvaluator.h"
+
+@implementation MPParenthesisFunction
+
++ (NSString *)localizedFunctionName
+{
+    return NSLocalizedString(@"Parenthesis", @"Name of Parenthesis Function");
+}
+
+- (instancetype)init
+{
+    self = [super init];
+    if (self) {
+        _expression = [[MPExpression alloc] init];
+        _expression.parent = self;
+    }
+    return self;
+}
+
+- (void)setExpression:(MPExpression *)expression
+{
+    _expression.parent = nil;
+    _expression = expression;
+    _expression.parent = self;
+}
+
+- (NSUInteger)numberOfChildren
+{
+    return 1;
+}
+
+- (MPExpression *)childAtIndex:(NSUInteger)index
+{
+    return index == 0 ? self.expression : nil;
+}
+
+- (void)setChild:(MPExpression *)child
+         atIndex:(NSUInteger)index
+{
+    if (index == 0) {
+        self.expression = child;
+    }
+}
+
+- (NSArray *)children
+{
+    return @[self.expression];
+}
+
+- (MPTerm *)parseWithError:(MPParseError *__autoreleasing *)error
+{
+    MPExpressionEvaluator *evaluator = self.expression.evaluator;
+    return [evaluator parseExpectingVariable:NO
+                                       error:error];
+}
+
+- (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error
+{
+    return [self.expression evaluateWithError:error];
+}
+
+- (NSString *)description
+{
+    return [NSString stringWithFormat:@"(%@)", self.expression.description];
+}
+
+- (NSUInteger)hash
+{
+#warning Unimplemented Method
+    return [super hash] * self.expression.hash;
+}
+
+- (id)copyWithZone:(NSZone *)zone
+{
+    MPParenthesisFunction *copy = [[MPParenthesisFunction allocWithZone:zone] init];
+    copy.expression = self.expression.copy;
+    return copy;
+}
+
+@end