Redesign of the Evaluation System

MathPad/MPParsedProduct.m

@@ -21,24 +21,37 @@
     return self;
 }
 
+- (instancetype)initWithFactor:(id<MPParsedFactor>)factor
+{
+    self = [super init];
+    if (self) {
+        _factors = [[NSMutableArray alloc] initWithObjects:factor, nil];
+    }
+    return self;
+}
+
 - (NSArray *)factors
 {
     return _factors;
 }
 
-- (void)addFactor:(MPParsedFactor *)factor
+- (void)addFactor:(id<MPParsedFactor>)factor
 {
     [_factors addObject:factor];
 }
 
-- (NSDecimalNumber *)value
+- (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error
 {
     if (_factors.count == 0) {
         return [NSDecimalNumber zero];
     }
     NSDecimalNumber *value = [NSDecimalNumber one];
-    for (MPParsedFactor *factor in _factors) {
-        value = [value decimalNumberByMultiplyingBy:factor.value];
+    for (id<MPParsedFactor> factor in _factors) {
+        NSDecimalNumber *factorValue = [factor evaluateWithError:error];
+        if (!factorValue) {
+            return nil;
+        }
+        value = [value decimalNumberByMultiplyingBy:factorValue];
     }
     return value;
 }