Added the MPExpressionTree Classes

MathPad/MPUnexpectedSymbolValue.m

@@ -0,0 +1,59 @@
+//
+//  MPUnidentifiedSymbolValue.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 11.10.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPUnexpectedSymbolValue.h"
+
+@implementation MPUnexpectedSymbolValue {
+    NSRange _range;
+}
+
+- (instancetype)init
+{
+    self = [super init];
+    if (self) {
+    }
+    return self;
+}
+
+- (instancetype)initWithTokenStream:(MPTokenStream *)tokenStream
+{
+    self = [self init];
+    if (self) {
+        [tokenStream beginIgnoringWhitespaceTokens];
+        _range = tokenStream.currentToken.range;
+        _symbol = tokenStream.currentToken.stringValue;
+        [tokenStream currentTokenConsumed];
+        [tokenStream endIgnoringOrAcceptingWhitespaceTokens];
+    }
+    return self;
+}
+
+- (NSRange)range
+{
+    return _range;
+}
+
+- (BOOL)validate:(MPParseError *__autoreleasing *)error
+{
+    if (error) {
+        *error = MPParseError(self.range, @"Unknown Symbol.");
+    }
+    return NO;
+}
+
+- (NSDecimalNumber *)evaluate
+{
+    return [NSDecimalNumber notANumber];
+}
+
+- (NSArray *)expressionElements
+{
+    return @[self.symbol];
+}
+
+@end