Added the MPExpressionTree Classes

MathPad/MPVariable.m

@@ -0,0 +1,68 @@
+//
+//  MPVariable.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 09.10.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPVariable.h"
+#import "MPEvaluationContext.h"
+
+@implementation MPVariable {
+    NSRange _range;
+}
+
+- (instancetype)init
+{
+    self = [super init];
+    if (self) {
+    }
+    return self;
+}
+
+- (instancetype)initWithTokenStream:(MPTokenStream *)tokenStream
+{
+    self = [self init];
+    if (self) {
+        [tokenStream beginIgnoringWhitespaceTokens];
+        MPToken *token = tokenStream.currentToken;
+        if (token.tokenType == MPVariableToken) {
+            self.variableName = token.stringValue;
+            _range = token.range;
+        } else {
+            @throw [NSException exceptionWithName:NSInternalInconsistencyException reason:@"Expected Variable" userInfo:nil];
+        }
+        [tokenStream currentTokenConsumed];
+        [tokenStream endIgnoringOrAcceptingWhitespaceTokens];
+    }
+    return self;
+}
+
+- (NSRange)range
+{
+    return _range;
+}
+
+- (BOOL)validate:(MPParseError *__autoreleasing *)error
+{
+    if (![[MPEvaluationContext sharedContext] isVariableDefined:self.variableName]) {
+        if (error) {
+            *error = MPParseError(self.range, @"Undefined Variable");
+        }
+        return NO;
+    }
+    return YES;
+}
+
+- (NSDecimalNumber *)evaluate
+{
+    return [[MPEvaluationContext sharedContext] valueForVariable:self.variableName];
+}
+
+- (NSArray *)expressionElements
+{
+    return @[self.variableName];
+}
+
+@end