Added the MPExpressionTree Classes

MathPad/MPExpression.m

@@ -14,7 +14,6 @@
 #import "MPException.h"
 
 #import "MPExpressionTokenizer.h"
-#import "MPExpressionEvaluator.h"
 #import "MPToken.h"
 
 
@@ -55,6 +54,11 @@
     return [self initWithElements:@[]];
 }
 
+- (instancetype)initWithExpressionTree:(MPExpressionTree *)expressionTree
+{
+    return [self initWithElements:expressionTree.expressionElements];
+}
+
 - (instancetype)initWithElement:(id<MPExpressionElement>)element
 {
     return [self initWithElements:@[element]];
@@ -518,13 +522,22 @@
 
 #pragma mark Evaluating Expressions
 
-
 - (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error
 {
-    MPExpressionEvaluator *evaluator = [[MPExpressionEvaluator alloc] initWithExpression:self];
-    MPTerm *term = [evaluator parseExpectingVariable:NO
-                                               error:error];
-    return [term evaluate];
+    MPExpressionTree *tree = [self parse];
+    if ([tree validate:error]) {
+        return [tree evaluate];
+    }
+    if (error) {
+        (*error).pathToExpression = self.indexPath;
+    }
+    return nil;
+}
+
+- (MPExpressionTree *)parse
+{
+    MPTokenStream *tokenStream = [[MPTokenStream alloc] initWithTokens:self.tokens];
+    return [[MPExpressionTree alloc] initWithTokenStream:tokenStream];
 }
 
 #pragma mark Notifications