Implemented Expression Evaluation/Parsing with Proper Error Handling

MathPad/MPParsedProduct.m

@@ -0,0 +1,51 @@
+//
+//  MPParsedSummand.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 10.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPParsedProduct.h"
+
+@implementation MPParsedProduct {
+    NSMutableArray *_factors;
+}
+
+- (instancetype)init
+{
+    self = [super init];
+    if (self) {
+        _factors = [[NSMutableArray alloc] init];
+    }
+    return self;
+}
+
+- (NSArray *)factors
+{
+    return _factors;
+}
+
+- (void)addFactor:(MPParsedFactor *)factor
+{
+    [_factors addObject:factor];
+}
+
+- (NSDecimalNumber *)value
+{
+    if (_factors.count == 0) {
+        return [NSDecimalNumber zero];
+    }
+    NSDecimalNumber *value = [NSDecimalNumber one];
+    for (MPParsedFactor *factor in _factors) {
+        value = [value decimalNumberByMultiplyingBy:factor.value];
+    }
+    return value;
+}
+
+- (NSString *)description
+{
+    return [NSString stringWithFormat:@"MPParsedProduct<%@>", [_factors componentsJoinedByString:@"*"]];
+}
+
+@end