Added the MPExpressionTree Classes

MathPad/MPParenthesisFunction.m

@@ -8,7 +8,6 @@
 //
 
 #import "MPParenthesisFunction.h"
-#import "MPExpressionEvaluator.h"
 
 @implementation MPParenthesisFunction
 
@@ -19,11 +18,14 @@ MPFunctionAccessorImplementation(Expression, _expression)
     return @[@"expression"];
 }
 
-- (MPTerm *)parseWithError:(MPParseError *__autoreleasing *)error
+- (BOOL)validate:(MPParseError *__autoreleasing *)error
 {
-    MPExpressionEvaluator *evaluator = [[MPExpressionEvaluator alloc] initWithExpression:self.expression];
-    return [evaluator parseExpectingVariable:NO
-                                       error:error];
+    return [[self.expression parse] validate:error];
+}
+
+- (NSDecimalNumber *)evaluate
+{
+    return [[self.expression parse] evaluate];
 }
 
 - (NSString *)description