Added the MPExpressionTree Classes

MathPad/MPFactorial.m

@@ -0,0 +1,58 @@
+//
+//  MPFactorial.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 11.10.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPFactorial.h"
+
+@implementation MPFactorial
+
+- (instancetype)init
+{
+    self = [super init];
+    if (self) {
+    }
+    return self;
+}
+
+- (instancetype)initWithTokenStream:(MPTokenStream *)tokenStream
+{
+    self = [self init];
+    if (self) {
+        [tokenStream beginIgnoringWhitespaceTokens];
+        if (tokenStream.currentToken.tokenType != MPFactorialToken) {
+            [tokenStream endIgnoringOrAcceptingWhitespaceTokens];
+            return nil;
+        } else {
+            [tokenStream currentTokenConsumed];
+        }
+        [tokenStream endIgnoringOrAcceptingWhitespaceTokens];
+    }
+    return self;
+}
+
+- (NSRange)range
+{
+    return NSMakeRange(0, 0);
+}
+
+- (BOOL)validate:(MPParseError *__autoreleasing *)error
+{
+    return [self.value validate:error];
+}
+
+- (NSDecimalNumber *)evaluate
+{
+    double value = [self.value evaluate].doubleValue;
+    return [[NSDecimalNumber alloc] initWithDouble:tgamma(value+1)];
+}
+
+- (NSArray *)expressionElements
+{
+    return @[@"!"];
+}
+
+@end